Gradle User Guide

Version 2.14.1

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.

Table of Contents

I. About Gradle
1. Introduction
2. Overview
II. Working with existing builds
3. Installing Gradle
4. Using the Gradle Command-Line
5. The Gradle Wrapper
6. The Gradle Daemon
7. Dependency Management Basics
8. Introduction to multi-project builds
9. Continuous build
10. Using the Gradle Graphical User Interface
11. The Build Environment
12. Troubleshooting
13. Embedding Gradle using the Tooling API
III. Writing Gradle build scripts
14. Build Script Basics
15. Build Init Plugin
16. Writing Build Scripts
17. More about Tasks
18. Working With Files
19. Using Ant from Gradle
20. The Build Lifecycle
21. Wrapper Plugin
22. Logging
23. Dependency Management
24. Multi-project Builds
25. Gradle Plugins
26. Standard Gradle plugins
27. The Project Report Plugin
28. The Build Dashboard Plugin
29. Comparing Builds
30. Publishing artifacts
31. The Maven Plugin
32. The Signing Plugin
33. Ivy Publishing (new)
34. Maven Publishing (new)
35. The Distribution Plugin
36. The Announce Plugin
37. The Build Announcements Plugin
IV. Extending the build
38. Writing Custom Task Classes
39. Writing Custom Plugins
40. The Java Gradle Plugin Development Plugin
41. Organizing Build Logic
42. Initialization Scripts
43. The Gradle TestKit
V. Building JVM projects
44. Java Quickstart
45. The Java Plugin
46. Web Application Quickstart
47. The War Plugin
48. The Ear Plugin
49. The Jetty Plugin
50. The Application Plugin
51. The Java Library Distribution Plugin
52. Groovy Quickstart
53. The Groovy Plugin
54. The Scala Plugin
55. The ANTLR Plugin
56. The Checkstyle Plugin
57. The CodeNarc Plugin
58. The FindBugs Plugin
59. The JDepend Plugin
60. The PMD Plugin
61. The JaCoCo Plugin
62. The Sonar Plugin
63. The SonarQube Runner Plugin
64. The OSGi Plugin
65. The Eclipse Plugins
66. The IDEA Plugin
VI. The Software model - Next generation Gradle builds
67. Rule based model configuration
68. Software model concepts
69. Implementing model rules in a plugin
70. Building Java Libraries
71. Building Play applications
72. Building native software
73. Extending the software model
VII. Appendix
A. Gradle Samples
B. Potential Traps
C. The Feature Lifecycle
D. Gradle Command Line
E. Documentation licenses
Glossary

List of Examples

4.1. Executing multiple tasks
4.2. Excluding tasks
4.3. Abbreviated task name
4.4. Abbreviated camel case task name
4.5. Selecting the project using a build file
4.6. Selecting the project using project directory
4.7. Forcing tasks to run
4.8. Obtaining information about projects
4.9. Providing a description for a project
4.10. Obtaining information about tasks
4.11. Changing the content of the task report
4.12. Obtaining more information about tasks
4.13. Obtaining detailed help for tasks
4.14. Obtaining information about dependencies
4.15. Filtering dependency report by configuration
4.16. Getting the insight into a particular dependency
4.17. Information about properties
5.1. Running the Wrapper task
5.2. Wrapper task
5.3. Wrapper generated files
5.4. Generating a SHA-256 hash
5.5. Configuring SHA-256 checksum verification
7.1. Declaring dependencies
7.2. Definition of an external dependency
7.3. Shortcut definition of an external dependency
7.4. Usage of Maven central repository
7.5. Usage of JCenter repository
7.6. Usage of a remote Maven repository
7.7. Usage of a remote Ivy directory
7.8. Usage of a local Ivy directory
7.9. Publishing to an Ivy repository
7.10. Publishing to a Maven repository
8.1. Listing the projects in a build
10.1. Launching the GUI
11.1. Setting properties with a gradle.properties file
11.2. Configuring an HTTP proxy
11.3. Configuring an HTTPS proxy
14.1. Your first build script
14.2. Execution of a build script
14.3. A task definition shortcut
14.4. Using Groovy in Gradle's tasks
14.5. Using Groovy in Gradle's tasks
14.6. Declaration of task that depends on other task
14.7. Lazy dependsOn - the other task does not exist (yet)
14.8. Dynamic creation of a task
14.9. Accessing a task via API - adding a dependency
14.10. Accessing a task via API - adding behaviour
14.11. Accessing task as a property of the build script
14.12. Adding extra properties to a task
14.13. Using AntBuilder to execute ant.loadfile target
14.14. Using methods to organize your build logic
14.15. Defining a default task
14.16. Different outcomes of build depending on chosen tasks
16.1. Accessing property of the Project object
16.2. Using local variables
16.3. Using extra properties
16.4. Configuring arbitrary objects
16.5. Configuring arbitrary objects using a script
16.6. Groovy JDK methods
16.7. Property accessors
16.8. Method call without parentheses
16.9. List and map literals
16.10. Closure as method parameter
16.11. Closure delegates
17.1. Defining tasks
17.2. Defining tasks - using strings for task names
17.3. Defining tasks with alternative syntax
17.4. Accessing tasks as properties
17.5. Accessing tasks via tasks collection
17.6. Accessing tasks by path
17.7. Creating a copy task
17.8. Configuring a task - various ways
17.9. Configuring a task - with closure
17.10. Defining a task with closure
17.11. Adding dependency on task from another project
17.12. Adding dependency using task object
17.13. Adding dependency using closure
17.14. Adding a 'must run after' task ordering
17.15. Adding a 'should run after' task ordering
17.16. Task ordering does not imply task execution
17.17. A 'should run after' task ordering is ignored if it introduces an ordering cycle
17.18. Adding a description to a task
17.19. Overwriting a task
17.20. Skipping a task using a predicate
17.21. Skipping tasks with StopExecutionException
17.22. Enabling and disabling tasks
17.23. A generator task
17.24. Declaring the inputs and outputs of a task
17.25. Task rule
17.26. Dependency on rule based tasks
17.27. Adding a task finalizer
17.28. Task finalizer for a failing task
18.1. Locating files
18.2. Creating a file collection
18.3. Using a file collection
18.4. Implementing a file collection
18.5. Creating a file tree
18.6. Using a file tree
18.7. Using an archive as a file tree
18.8. Specifying a set of files
18.9. Copying files using the copy task
18.10. Specifying copy task source files and destination directory
18.11. Selecting the files to copy
18.12. Copying files using the copy() method without up-to-date check
18.13. Copying files using the copy() method with up-to-date check
18.14. Renaming files as they are copied
18.15. Filtering files as they are copied
18.16. Nested copy specs
18.17. Using the Sync task to copy dependencies
18.18. Creating a ZIP archive
18.19. Creation of ZIP archive
18.20. Configuration of archive task - custom archive name
18.21. Configuration of archive task - appendix & classifier
19.1. Using an Ant task
19.2. Passing nested text to an Ant task
19.3. Passing nested elements to an Ant task
19.4. Using an Ant type
19.5. Using a custom Ant task
19.6. Declaring the classpath for a custom Ant task
19.7. Using a custom Ant task and dependency management together
19.8. Importing an Ant build
19.9. Task that depends on Ant target
19.10. Adding behaviour to an Ant target
19.11. Ant target that depends on Gradle task
19.12. Renaming imported Ant targets
19.13. Setting an Ant property
19.14. Getting an Ant property
19.15. Setting an Ant reference
19.16. Getting an Ant reference
19.17. Fine tuning Ant logging
20.1. Single project build
20.2. Hierarchical layout
20.3. Flat layout
20.4. Modification of elements of the project tree
20.5. Adding of test task to each project which has certain property set
20.6. Notifications
20.7. Setting of certain property to all tasks
20.8. Logging of start and end of each task execution
22.1. Using stdout to write log messages
22.2. Writing your own log messages
22.3. Using SLF4J to write log messages
22.4. Configuring standard output capture
22.5. Configuring standard output capture for a task
22.6. Customizing what Gradle logs
23.1. Definition of a configuration
23.2. Accessing a configuration
23.3. Configuration of a configuration
23.4. Module dependencies
23.5. Artifact only notation
23.6. Dependency with classifier
23.7. Iterating over a configuration
23.8. Client module dependencies - transitive dependencies
23.9. Project dependencies
23.10. File dependencies
23.11. Generated file dependencies
23.12. Gradle API dependencies
23.13. Gradle's Groovy dependencies
23.14. Excluding transitive dependencies
23.15. Optional attributes of dependencies
23.16. Collections and arrays of dependencies
23.17. Dependency configurations
23.18. Dependency configurations for project
23.19. Configuration.copy
23.20. Accessing declared dependencies
23.21. Configuration.files
23.22. Configuration.files with spec
23.23. Configuration.copy
23.24. Configuration.copy vs. Configuration.files
23.25. Adding central Maven repository
23.26. Adding Bintray's JCenter Maven repository
23.27. Using Bintrays's JCenter with HTTP
23.28. Adding the local Maven cache as a repository
23.29. Adding custom Maven repository
23.30. Adding additional Maven repositories for JAR files
23.31. Accessing password protected Maven repository
23.32. Flat repository resolver
23.33. Ivy repository
23.34. Ivy repository with named layout
23.35. Ivy repository with pattern layout
23.36. Ivy repository with multiple custom patterns
23.37. Ivy repository with Maven compatible layout
23.38. Ivy repository
23.39. Declaring a Maven and Ivy repository
23.40. Providing credentials to a Maven and Ivy repository
23.41. Declaring a S3 backed Maven and Ivy repository
23.42. Configure repository to use only digest authentication
23.43. Configure repository to use preemptive authentication
23.44. Accessing a repository
23.45. Configuration of a repository
23.46. Definition of a custom repository
23.47. Forcing consistent version for a group of libraries
23.48. Using a custom versioning scheme
23.49. Blacklisting a version with a replacement
23.50. Changing dependency group and/or name at the resolution
23.51. Substituting a module with a project
23.52. Substituting a project with a module
23.53. Conditionally substituting a dependency
23.54. Specifying default dependencies on a configuration
23.55. Enabling dynamic resolve mode
23.56. 'Latest' version selector
23.57. Custom status scheme
23.58. Custom status scheme by module
23.59. Ivy component metadata rule
23.60. Rule source component metadata rule
23.61. Component selection rule
23.62. Component selection rule with module target
23.63. Component selection rule with metadata
23.64. Component selection rule using a rule source object
23.65. Declaring module replacement
23.66. Dynamic version cache control
23.67. Changing module cache control
24.1. Multi-project tree - water & bluewhale projects
24.2. Build script of water (parent) project
24.3. Multi-project tree - water, bluewhale & krill projects
24.4. Water project build script
24.5. Defining common behavior of all projects and subprojects
24.6. Defining specific behaviour for particular project
24.7. Defining specific behaviour for project krill
24.8. Adding custom behaviour to some projects (filtered by project name)
24.9. Adding custom behaviour to some projects (filtered by project properties)
24.10. Running build from subproject
24.11. Evaluation and execution of projects
24.12. Evaluation and execution of projects
24.13. Running tasks by their absolute path
24.14. Dependencies and execution order
24.15. Dependencies and execution order
24.16. Dependencies and execution order
24.17. Declaring dependencies
24.18. Declaring dependencies
24.19. Cross project task dependencies
24.20. Configuration time dependencies
24.21. Configuration time dependencies - evaluationDependsOn
24.22. Configuration time dependencies
24.23. Dependencies - real life example - crossproject configuration
24.24. Project lib dependencies
24.25. Project lib dependencies
24.26. Fine grained control over dependencies
24.27. Build and Test Single Project
24.28. Partial Build and Test Single Project
24.29. Build and Test Depended On Projects
24.30. Build and Test Dependent Projects
25.1. Applying a script plugin
25.2. Applying a binary plugin
25.3. Applying a binary plugin by type
25.4. Applying a plugin with the buildscript block
25.5. Applying a core plugin
25.6. Applying a community plugin
25.7. Using plugins from custom plugin repositories.
25.8. Complete Plugin Publishing Sample
28.1. Using the Build Dashboard plugin
30.1. Defining an artifact using an archive task
30.2. Defining an artifact using a file
30.3. Customizing an artifact
30.4. Map syntax for defining an artifact using a file
30.5. Configuration of the upload task
31.1. Using the Maven plugin
31.2. Creating a stand alone pom.
31.3. Upload of file to remote Maven repository
31.4. Upload of file via SSH
31.5. Customization of pom
31.6. Builder style customization of pom
31.7. Modifying auto-generated content
31.8. Customization of Maven installer
31.9. Generation of multiple poms
31.10. Accessing a mapping configuration
32.1. Using the Signing plugin
32.2. Signing a configuration
32.3. Signing a configuration output
32.4. Signing a task
32.5. Signing a task output
32.6. Conditional signing
32.7. Signing a POM for deployment
33.1. Applying the “ivy-publish” plugin
33.2. Publishing a Java module to Ivy
33.3. Publishing additional artifact to Ivy
33.4. customizing the publication identity
33.5. Customizing the module descriptor file
33.6. Publishing multiple modules from a single project
33.7. Declaring repositories to publish to
33.8. Choosing a particular publication to publish
33.9. Publishing all publications via the “publish” lifecycle task
33.10. Generating the Ivy module descriptor file
33.11. Publishing a Java module
33.12. Example generated ivy.xml
34.1. Applying the 'maven-publish' plugin
34.2. Adding a MavenPublication for a Java component
34.3. Adding additional artifact to a MavenPublication
34.4. customizing the publication identity
34.5. Modifying the POM file
34.6. Publishing multiple modules from a single project
34.7. Declaring repositories to publish to
34.8. Publishing a project to a Maven repository
34.9. Publish a project to the Maven local repository
34.10. Generate a POM file without publishing
35.1. Using the distribution plugin
35.2. Adding extra distributions
35.3. Configuring the main distribution
35.4. publish main distribution
36.1. Using the announce plugin
36.2. Configure the announce plugin
36.3. Using the announce plugin
37.1. Using the build announcements plugin
37.2. Using the build announcements plugin from an init script
38.1. Defining a custom task
38.2. A hello world task
38.3. A customizable hello world task
38.4. A build for a custom task
38.5. A custom task
38.6. Using a custom task in another project
38.7. Testing a custom task
38.8. Defining an incremental task action
38.9. Running the incremental task for the first time
38.10. Running the incremental task with unchanged inputs
38.11. Running the incremental task with updated input files
38.12. Running the incremental task with an input file removed
38.13. Running the incremental task with an output file removed
38.14. Running the incremental task with an input property changed
39.1. A custom plugin
39.2. A custom plugin extension
39.3. A custom plugin with configuration closure
39.4. Evaluating file properties lazily
39.5. A build for a custom plugin
39.6. Wiring for a custom plugin
39.7. Using a custom plugin in another project
39.8. Applying a community plugin with the plugins DSL
39.9. Testing a custom plugin
39.10. Using the Java Gradle Plugin Development plugin
39.11. Managing domain objects
40.1. Using the Java Gradle Plugin Development plugin
40.2. Using the gradlePlugin {} block.
41.1. Using inherited properties and methods
41.2. Using injected properties and methods
41.3. Configuring the project using an external build script
41.4. Custom buildSrc build script
41.5. Adding subprojects to the root buildSrc project
41.6. Running another build from a build
41.7. Declaring external dependencies for the build script
41.8. A build script with external dependencies
41.9. Ant optional dependencies
42.1. Using init script to perform extra configuration before projects are evaluated
42.2. Declaring external dependencies for an init script
42.3. An init script with external dependencies
42.4. Using plugins in init scripts
43.1. Declaring the TestKit dependency
43.2. Declaring the JUnit dependency
43.3. Using GradleRunner with JUnit
43.4. Using GradleRunner with Spock
43.5. Making the code under test classpath available to the tests
43.6. Injecting the code under test classes into test builds
43.7. Using the Java Gradle Development plugin for generating the plugin metadata
43.8. Automatically injecting the code under test classes into test builds
43.9. Reconfiguring the classpath generation conventions of the Java Gradle Development plugin
43.10. Specifying a Gradle version for test execution
44.1. Using the Java plugin
44.2. Building a Java project
44.3. Adding Maven repository
44.4. Adding dependencies
44.5. Customization of MANIFEST.MF
44.6. Adding a test system property
44.7. Publishing the JAR file
44.8. Eclipse plugin
44.9. Java example - complete build file
44.10. Multi-project build - hierarchical layout
44.11. Multi-project build - settings.gradle file
44.12. Multi-project build - common configuration
44.13. Multi-project build - dependencies between projects
44.14. Multi-project build - distribution file
45.1. Using the Java plugin
45.2. Custom Java source layout
45.3. Accessing a source set
45.4. Configuring the source directories of a source set
45.5. Defining a source set
45.6. Defining source set dependencies
45.7. Compiling a source set
45.8. Assembling a JAR for a source set
45.9. Generating the Javadoc for a source set
45.10. Running tests in a source set
45.11. Filtering tests in the build script
45.12. JUnit Categories
45.13. Grouping TestNG tests
45.14. Preserving order of TestNG tests
45.15. Grouping TestNG tests by instances
45.16. Creating a unit test report for subprojects
45.17. Customization of MANIFEST.MF
45.18. Creating a manifest object.
45.19. Separate MANIFEST.MF for a particular archive
46.1. War plugin
46.2. Running web application with Jetty plugin
47.1. Using the War plugin
47.2. Customization of war plugin
48.1. Using the Ear plugin
48.2. Customization of ear plugin
49.1. Using the Jetty plugin
50.1. Using the application plugin
50.2. Configure the application main class
50.3. Configure default JVM settings
50.4. Include output from other tasks in the application distribution
50.5. Automatically creating files for distribution
51.1. Using the Java library distribution plugin
51.2. Configure the distribution name
51.3. Include files in the distribution
52.1. Groovy plugin
52.2. Dependency on Groovy
52.3. Groovy example - complete build file
53.1. Using the Groovy plugin
53.2. Custom Groovy source layout
53.3. Configuration of Groovy dependency
53.4. Configuration of Groovy test dependency
53.5. Configuration of bundled Groovy dependency
53.6. Configuration of Groovy file dependency
54.1. Using the Scala plugin
54.2. Custom Scala source layout
54.3. Declaring a Scala dependency for production code
54.4. Declaring a Scala dependency for test code
54.5. Adjusting memory settings
54.6. Forcing all code to be compiled
54.7. Explicitly specify a target IntelliJ IDEA version
55.1. Using the ANTLR plugin
55.2. Declare ANTLR version
55.3. setting custom max heap size and extra arguments for ANTLR
56.1. Using the Checkstyle plugin
56.2. Customizing the HTML report
57.1. Using the CodeNarc plugin
58.1. Using the FindBugs plugin
58.2. Customizing the HTML report
59.1. Using the JDepend plugin
60.1. Using the PMD plugin
61.1. Applying the JaCoCo plugin
61.2. Configuring JaCoCo plugin settings
61.3. Configuring test task
61.4. Configuring test task
61.5. Using application plugin to generate code coverage data
61.6. Coverage reports generated by applicationCodeCoverageReport
62.1. Applying the Sonar plugin
62.2. Configuring Sonar connection settings
62.3. Configuring Sonar project settings
62.4. Global configuration in a multi-project build
62.5. Common project configuration in a multi-project build
62.6. Individual project configuration in a multi-project build
62.7. Configuring the language to be analyzed
62.8. Using property syntax
62.9. Analyzing custom source sets
62.10. Analyzing languages other than Java
62.11. Setting custom global properties
62.12. Setting custom project properties
62.13. Implementing custom command line properties
63.1. Applying the SonarQube Runner plugin
63.2. Configuring SonarQube connection settings
63.3. Configuring SonarQube runner version
63.4. Global configuration settings
63.5. Shared configuration settings
63.6. Individual configuration settings
63.7. Skipping analysis of a project
63.8. Analyzing custom source sets
63.9. Analyzing languages other than Java
63.10. setting custom SonarQube Runner fork options
64.1. Using the OSGi plugin
64.2. Configuration of OSGi MANIFEST.MF file
65.1. Using the Eclipse plugin
65.2. Using the Eclipse WTP plugin
65.3. Partial Overwrite for Classpath
65.4. Partial Overwrite for Project
65.5. Export Dependencies
65.6. Customizing the XML
66.1. Using the IDEA plugin
66.2. Partial Rewrite for Module
66.3. Partial Rewrite for Project
66.4. Export Dependencies
66.5. Customizing the XML
67.1. applying a rule source plugin
67.2. a model creation rule
67.3. a model mutation rule
67.4. creating a task
67.5. a managed type
67.6. a String property
67.7. a File property
67.8. a Long property
67.9. a boolean property
67.10. an int property
67.11. a managed property
67.12. an enumeration type property
67.13. a managed set
67.14. strongly modelling sources sets
67.15. a DSL example applying a rule to every element in a scope
67.16. DSL configuration rule
67.17. Configuration run when required
67.18. Configuration not run when not required
67.19. DSL creation rule
67.20. DSL creation rule without initialization
67.21. Initialization before configuration
67.22. Nested DSL creation rule
67.23. Nested DSL configuration rule
67.24. DSL configuration rule for each element in a map
67.25. Nested DSL property configuration
67.26. a DSL example showing type conversions
67.27. a DSL rule using inputs
67.28. model task output
70.1. Using the Java software plugins
70.2. Creating a java library
70.3. Configuring a source set
70.4. Creating a new source set
70.5. The components report
70.6. Declaring a dependency onto a library
70.7. Declaring a dependency onto a project with an explicit library
70.8. Declaring a dependency onto a project with an implicit library
70.9. Declaring a dependency onto a library published to a Maven repository
70.10. Declaring a module dependency using shorthand notation
70.11. Configuring repositories for dependency resolution
70.12. Specifying api packages
70.13. Specifying api dependencies
70.14. Main sources
70.15. Client component
70.16. Broken client component
70.17. Recompiling the client
70.18. Declaring target platforms
70.19. Declaring binary specific sources
70.20. Declaring target platforms
70.21. Using the JUnit plugin
70.22. Executing the test suite
70.23. Executing the test suite
70.24. Declaring a component under test
70.25. Declaring local Java installations
71.1. Using the Play plugin
71.2. The components report
71.3. Selecting a version of the Play Framework
71.4. Adding dependencies to a Play application
71.5. Adding extra source sets to a Play application
71.6. Configuring Scala compiler options
71.7. Configuring routes style
71.8. Configuring a custom asset pipeline
71.9. Configuring dependencies on Play subprojects
71.10. Add extra files to a Play application distribution
71.11. Applying both the Play and IDEA plugins
72.1. Defining a library component
72.2. Defining executable components
72.3. The components report
72.4. The 'cpp' plugin
72.5. C++ source set
72.6. The 'c' plugin
72.7. C source set
72.8. The 'assembler' plugin
72.9. The 'objective-c' plugin
72.10. The 'objective-cpp' plugin
72.11. Settings that apply to all binaries
72.12. Settings that apply to all shared libraries
72.13. Settings that apply to all binaries produced for the 'main' executable component
72.14. Settings that apply only to shared libraries produced for the 'main' library component
72.15. The 'windows-resources' plugin
72.16. Configuring the location of Windows resource sources
72.17. Building a resource-only dll
72.18. Providing a library dependency to the source set
72.19. Providing a library dependency to the binary
72.20. Declaring project dependencies
72.21. Creating a precompiled header file
72.22. Including a precompiled header file in a source file
72.23. Configuring a precompiled header
72.24. Defining build types
72.25. Configuring debug binaries
72.26. Defining platforms
72.27. Defining flavors
72.28. Targeting a component at particular platforms
72.29. Building all possible variants
72.30. Defining tool chains
72.31. Reconfigure tool arguments
72.32. Defining target platforms
72.33. Registering CUnit tests
72.34. Running CUnit tests
72.35. Registering GoogleTest tests
73.1. an example of using a custom software model
73.2. Declare a custom component
73.3. Register a custom component
73.4. Declare a custom binary
73.5. Register a custom binary
73.6. Declare a custom source set
73.7. Register a custom source set
73.8. Generates documentation binaries
73.9. Generates tasks for text source sets
73.10. Register a custom source set
73.11. an example of using a custom software model
73.12. foo bar
73.13. public type and internal view declaration
73.14. type registration
73.15. public and internal data mutation
73.16. example build script and model report output
B.1. Variables scope: local and script wide
B.2. Distinct configuration and execution phase

Part I. About Gradle

Chapter 1. Introduction

We would like to introduce Gradle to you, a build system that we think is a quantum leap for build technology in the Java (JVM) world. Gradle provides:

  • A very flexible general purpose build tool like Ant.

  • Switchable, build-by-convention frameworks a la Maven. But we never lock you in!

  • Very powerful support for multi-project builds.

  • Very powerful dependency management (based on Apache Ivy).

  • Full support for your existing Maven or Ivy repository infrastructure.

  • Support for transitive dependency management without the need for remote repositories or pom.xml and ivy.xml files.

  • Ant tasks and builds as first class citizens.

  • Groovy build scripts.

  • A rich domain model for describing your build.

In Chapter 2, Overview you will find a detailed overview of Gradle. Otherwise, the tutorials are waiting, have fun :)

1.1. About this user guide

This user guide, like Gradle itself, is under very active development. Some parts of Gradle aren't documented as completely as they need to be. Some of the content presented won't be entirely clear or will assume that you know more about Gradle than you do. We need your help to improve this user guide. You can find out more about contributing to the documentation at the Gradle web site.

Throughout the user guide, you will find some diagrams that represent dependency relationships between Gradle tasks. These use something analogous to the UML dependency notation, which renders an arrow from one task to the task that the first task depends on.

Chapter 2. Overview

2.1. Features

Here is a list of some of Gradle's features.

Declarative builds and build-by-convention

At the heart of Gradle lies a rich extensible Domain Specific Language (DSL) based on Groovy. Gradle pushes declarative builds to the next level by providing declarative language elements that you can assemble as you like. Those elements also provide build-by-convention support for Java, Groovy, OSGi, Web and Scala projects. Even more, this declarative language is extensible. Add your own new language elements or enhance the existing ones, thus providing concise, maintainable and comprehensible builds.

Language for dependency based programming

The declarative language lies on top of a general purpose task graph, which you can fully leverage in your builds. It provides utmost flexibility to adapt Gradle to your unique needs.

Structure your build

The suppleness and richness of Gradle finally allows you to apply common design principles to your build. For example, it is very easy to compose your build from reusable pieces of build logic. Inline stuff where unnecessary indirections would be inappropriate. Don't be forced to tear apart what belongs together (e.g. in your project hierarchy). Avoid smells like shotgun changes or divergent change that turn your build into a maintenance nightmare. At last you can create a well structured, easily maintained, comprehensible build.

Deep API

From being a pleasure to be used embedded to its many hooks over the whole lifecycle of build execution, Gradle allows you to monitor and customize its configuration and execution behavior to its very core.

Gradle scales

Gradle scales very well. It significantly increases your productivity, from simple single project builds up to huge enterprise multi-project builds. This is true for structuring the build. With the state-of-art incremental build function, this is also true for tackling the performance pain many large enterprise builds suffer from.

Multi-project builds

Gradle's support for multi-project build is outstanding. Project dependencies are first class citizens. We allow you to model the project relationships in a multi-project build as they really are for your problem domain. Gradle follows your layout not vice versa.

Gradle provides partial builds. If you build a single subproject Gradle takes care of building all the subprojects that subproject depends on. You can also choose to rebuild the subprojects that depend on a particular subproject. Together with incremental builds this is a big time saver for larger builds.

Many ways to manage your dependencies

Different teams prefer different ways to manage their external dependencies. Gradle provides convenient support for any strategy. From transitive dependency management with remote Maven and Ivy repositories to jars or directories on the local file system.

Gradle is the first build integration tool

Ant tasks are first class citizens. Even more interesting, Ant projects are first class citizens as well. Gradle provides a deep import for any Ant project, turning Ant targets into native Gradle tasks at runtime. You can depend on them from Gradle, you can enhance them from Gradle, you can even declare dependencies on Gradle tasks in your build.xml. The same integration is provided for properties, paths, etc ...

Gradle fully supports your existing Maven or Ivy repository infrastructure for publishing and retrieving dependencies. Gradle also provides a converter for turning a Maven pom.xml into a Gradle script. Runtime imports of Maven projects will come soon.

Ease of migration

Gradle can adapt to any structure you have. Therefore you can always develop your Gradle build in the same branch where your production build lives and both can evolve in parallel. We usually recommend to write tests that make sure that the produced artifacts are similar. That way migration is as less disruptive and as reliable as possible. This is following the best-practices for refactoring by applying baby steps.

Groovy

Gradle's build scripts are written in Groovy, not XML. But unlike other approaches this is not for simply exposing the raw scripting power of a dynamic language. That would just lead to a very difficult to maintain build. The whole design of Gradle is oriented towards being used as a language, not as a rigid framework. And Groovy is our glue that allows you to tell your individual story with the abstractions Gradle (or you) provide. Gradle provides some standard stories but they are not privileged in any form. This is for us a major distinguishing feature compared to other declarative build systems. Our Groovy support is not just sugar coating. The whole Gradle API is fully Groovy-ized. Adding Groovy results in an enjoyable and productive experience.

The Gradle wrapper

The Gradle Wrapper allows you to execute Gradle builds on machines where Gradle is not installed. This is useful for example for some continuous integration servers. It is also useful for an open source project to keep the barrier low for building it. The wrapper is also very interesting for the enterprise. It is a zero administration approach for the client machines. It also enforces the usage of a particular Gradle version thus minimizing support issues.

Free and open source

Gradle is an open source project, and is licensed under the ASL.

2.2. Why Groovy?

We think the advantages of an internal DSL (based on a dynamic language) over XML are tremendous when used in build scripts. There are a couple of dynamic languages out there. Why Groovy? The answer lies in the context Gradle is operating in. Although Gradle is a general purpose build tool at its core, its main focus are Java projects. In such projects the team members will be very familiar with Java. We think a build should be as transparent as possible to all team members.

In that case, you might argue why we don't just use Java as the language for build scripts. We think this is a valid question. It would have the highest transparency for your team and the lowest learning curve, but because of the limitations of Java, such a build language would not be as nice, expressive and powerful as it could be. [1] Languages like Python, Groovy or Ruby do a much better job here. We have chosen Groovy as it offers by far the greatest transparency for Java people. Its base syntax is the same as Java's as well as its type system, its package structure and other things. Groovy provides much more on top of that, but with the common foundation of Java.

For Java developers with Python or Ruby knowledge or the desire to learn them, the above arguments don't apply. The Gradle design is well-suited for creating another build script engine in JRuby or Jython. It just doesn't have the highest priority for us at the moment. We happily support any community effort to create additional build script engines.



[1] At http://www.defmacro.org/ramblings/lisp.html you find an interesting article comparing Ant, XML, Java and Lisp. It's funny that the 'if Java had that syntax' syntax in this article is actually the Groovy syntax.

Part II. Working with existing builds

Chapter 3. Installing Gradle

3.1. Prerequisites

Gradle requires a Java JDK or JRE to be installed, version 6 or higher (to check, use java -version). Gradle ships with its own Groovy library, therefore Groovy does not need to be installed. Any existing Groovy installation is ignored by Gradle.

Gradle uses whatever JDK it finds in your path. Alternatively, you can set the JAVA_HOME environment variable to point to the installation directory of the desired JDK.

3.2. Download

You can download one of the Gradle distributions from the Gradle web site.

3.3. Unpacking

The Gradle distribution comes packaged as a ZIP. The full distribution contains:

  • The Gradle binaries.

  • The user guide (HTML and PDF).

  • The DSL reference guide.

  • The API documentation (Javadoc and Groovydoc).

  • Extensive samples, including the examples referenced in the user guide, along with some complete and more complex builds you can use as a starting point for your own build.

  • The binary sources. This is for reference only. If you want to build Gradle you need to download the source distribution or checkout the sources from the source repository. See the Gradle web site for details.

3.4. Environment variables

For running Gradle, firstly add the environment variable GRADLE_HOME. This should point to the unpacked files from the Gradle website. Next add GRADLE_HOME/bin to your PATH environment variable. Usually, this is sufficient to run Gradle.

3.5. Running and testing your installation

You run Gradle via the gradle command. To check if Gradle is properly installed just type gradle -v. The output shows the Gradle version and also the local environment configuration (Groovy, JVM version, OS, etc.). The displayed Gradle version should match the distribution you have downloaded.

3.6. JVM options

JVM options for running Gradle can be set via environment variables. You can use either GRADLE_OPTS or JAVA_OPTS, or both. JAVA_OPTS is by convention an environment variable shared by many Java applications. A typical use case would be to set the HTTP proxy in JAVA_OPTS and the memory options in GRADLE_OPTS. Those variables can also be set at the beginning of the gradle or gradlew script.

Note that it's not currently possible to set JVM options for Gradle on the command line.

Chapter 4. Using the Gradle Command-Line

This chapter introduces the basics of the Gradle command-line. You run a build using the gradle command, which you have already seen in action in previous chapters.

4.1. Executing multiple tasks

You can execute multiple tasks in a single build by listing each of the tasks on the command-line. For example, the command gradle compile test will execute the compile and test tasks. Gradle will execute the tasks in the order that they are listed on the command-line, and will also execute the dependencies for each task. Each task is executed once only, regardless of how it came to be included in the build: whether it was specified on the command-line, or as a dependency of another task, or both. Let's look at an example.

Below four tasks are defined. Both dist and test depend on the compile task. Running gradle dist test for this build script results in the compile task being executed only once.

Figure 4.1. Task dependencies

Task dependencies

Example 4.1. Executing multiple tasks

build.gradle

task compile << {
    println 'compiling source'
}

task compileTest(dependsOn: compile) << {
    println 'compiling unit tests'
}

task test(dependsOn: [compile, compileTest]) << {
    println 'running unit tests'
}

task dist(dependsOn: [compile, test]) << {
    println 'building the distribution'
}

Output of gradle dist test

> gradle dist test
:compile
compiling source
:compileTest
compiling unit tests
:test
running unit tests
:dist
building the distribution

BUILD SUCCESSFUL

Total time: 1 secs

Each task is executed only once, so gradle test test is exactly the same as gradle test.

4.2. Excluding tasks

You can exclude a task from being executed using the -x command-line option and providing the name of the task to exclude. Let's try this with the sample build file above.

Example 4.2. Excluding tasks

Output of gradle dist -x test

> gradle dist -x test
:compile
compiling source
:dist
building the distribution

BUILD SUCCESSFUL

Total time: 1 secs

You can see from the output of this example, that the test task is not executed, even though it is a dependency of the dist task. You will also notice that the test task's dependencies, such as compileTest are not executed either. Those dependencies of test that are required by another task, such as compile, are still executed.

4.3. Continuing the build when a failure occurs

By default, Gradle will abort execution and fail the build as soon as any task fails. This allows the build to complete sooner, but hides other failures that would have occurred. In order to discover as many failures as possible in a single build execution, you can use the --continue option.

When executed with --continue, Gradle will execute every task to be executed where all of the dependencies for that task completed without failure, instead of stopping as soon as the first failure is encountered. Each of the encountered failures will be reported at the end of the build.

If a task fails, any subsequent tasks that were depending on it will not be executed, as it is not safe to do so. For example, tests will not run if there is a compilation failure in the code under test; because the test task will depend on the compilation task (either directly or indirectly).

4.4. Task name abbreviation

When you specify tasks on the command-line, you don't have to provide the full name of the task. You only need to provide enough of the task name to uniquely identify the task. For example, in the sample build above, you can execute task dist by running gradle d:

Example 4.3. Abbreviated task name

Output of gradle di

> gradle di
:compile
compiling source
:compileTest
compiling unit tests
:test
running unit tests
:dist
building the distribution

BUILD SUCCESSFUL

Total time: 1 secs

You can also abbreviate each word in a camel case task name. For example, you can execute task compileTest by running gradle compTest or even gradle cT

Example 4.4. Abbreviated camel case task name

Output of gradle cT

> gradle cT
:compile
compiling source
:compileTest
compiling unit tests

BUILD SUCCESSFUL

Total time: 1 secs

You can also use these abbreviations with the -x command-line option.

4.5. Selecting which build to execute

When you run the gradle command, it looks for a build file in the current directory. You can use the -b option to select another build file. If you use -b option then settings.gradle file is not used. Example:

Example 4.5. Selecting the project using a build file

subdir/myproject.gradle

task hello << {
    println "using build file '$buildFile.name' in '$buildFile.parentFile.name'."
}

Output of gradle -q -b subdir/myproject.gradle hello

> gradle -q -b subdir/myproject.gradle hello
using build file 'myproject.gradle' in 'subdir'.

Alternatively, you can use the -p option to specify the project directory to use. For multi-project builds you should use -p option instead of -b option.

Example 4.6. Selecting the project using project directory

Output of gradle -q -p subdir hello

> gradle -q -p subdir hello
using build file 'build.gradle' in 'subdir'.

4.6. Forcing tasks to execute

Many tasks, particularly those provided by Gradle itself, support incremental builds. Such tasks can determine whether they need to run or not based on whether their inputs or outputs have changed since the last time they ran. You can easily identify incremental tasks when Gradle displays the text UP-TO-DATE next to their name when executing a build.

You may on occasion want to force Gradle to run all the tasks, ignoring any up-to-date checks. If that's the case, simply use the --rerun-tasks option. Here's the output when running a task both without and with --rerun-tasks:

Example 4.7. Forcing tasks to run

Output of gradle doIt

> gradle doIt
:doIt UP-TO-DATE

Output of gradle --rerun-tasks doIt

> gradle --rerun-tasks doIt
:doIt

Note that this will force all required tasks to execute, not just the ones you specify on the command line. It's a little like running a clean, but without the build's generated output being deleted.

4.7. Obtaining information about your build

Gradle provides several built-in tasks which show particular details of your build. This can be useful for understanding the structure and dependencies of your build, and for debugging problems.

In addition to the built-in tasks shown below, you can also use the project report plugin to add tasks to your project which will generate these reports.

4.7.1. Listing projects

Running gradle projects gives you a list of the sub-projects of the selected project, displayed in a hierarchy. Here is an example:

Example 4.8. Obtaining information about projects

Output of gradle -q projects

> gradle -q projects

------------------------------------------------------------
Root project
------------------------------------------------------------

Root project 'projectReports'
+--- Project ':api' - The shared API for the application
\--- Project ':webapp' - The Web application implementation

To see a list of the tasks of a project, run gradle <project-path>:tasks
For example, try running gradle :api:tasks

The report shows the description of each project, if specified. You can provide a description for a project by setting the description property:

Example 4.9. Providing a description for a project

build.gradle

description = 'The shared API for the application'

4.7.2. Listing tasks

Running gradle tasks gives you a list of the main tasks of the selected project. This report shows the default tasks for the project, if any, and a description for each task. Below is an example of this report:

Example 4.10. Obtaining information about tasks

Output of gradle -q tasks

> gradle -q tasks

------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------

Default tasks: dists

Build tasks
-----------
clean - Deletes the build directory (build)
dists - Builds the distribution
libs - Builds the JAR

Build Setup tasks
-----------------
init - Initializes a new Gradle build. [incubating]
wrapper - Generates Gradle wrapper files. [incubating]

Help tasks
----------
buildEnvironment - Displays all buildscript dependencies declared in root project 'projectReports'.
components - Displays the components produced by root project 'projectReports'. [incubating]
dependencies - Displays all dependencies declared in root project 'projectReports'.
dependencyInsight - Displays the insight into a specific dependency in root project 'projectReports'.
help - Displays a help message.
model - Displays the configuration model of root project 'projectReports'. [incubating]
projects - Displays the sub-projects of root project 'projectReports'.
properties - Displays the properties of root project 'projectReports'.
tasks - Displays the tasks runnable from root project 'projectReports' (some of the displayed tasks may belong to subprojects).

To see all tasks and more detail, run gradle tasks --all

To see more detail about a task, run gradle help --task <task>

By default, this report shows only those tasks which have been assigned to a task group. You can do this by setting the group property for the task. You can also set the description property, to provide a description to be included in the report.

Example 4.11. Changing the content of the task report

build.gradle

dists {
    description = 'Builds the distribution'
    group = 'build'
}

You can obtain more information in the task listing using the --all option. With this option, the task report lists all tasks in the project, grouped by main task, and the dependencies for each task. Here is an example:

Example 4.12. Obtaining more information about tasks

Output of gradle -q tasks --all

> gradle -q tasks --all

------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------

Default tasks: dists

Build tasks
-----------
clean - Deletes the build directory (build)
api:clean - Deletes the build directory (build)
webapp:clean - Deletes the build directory (build)
dists - Builds the distribution [api:libs, webapp:libs]
    docs - Builds the documentation
api:libs - Builds the JAR
    api:compile - Compiles the source files
webapp:libs - Builds the JAR [api:libs]
    webapp:compile - Compiles the source files

Build Setup tasks
-----------------
init - Initializes a new Gradle build. [incubating]
wrapper - Generates Gradle wrapper files. [incubating]

Help tasks
----------
buildEnvironment - Displays all buildscript dependencies declared in root project 'projectReports'.
api:buildEnvironment - Displays all buildscript dependencies declared in project ':api'.
webapp:buildEnvironment - Displays all buildscript dependencies declared in project ':webapp'.
components - Displays the components produced by root project 'projectReports'. [incubating]
api:components - Displays the components produced by project ':api'. [incubating]
webapp:components - Displays the components produced by project ':webapp'. [incubating]
dependencies - Displays all dependencies declared in root project 'projectReports'.
api:dependencies - Displays all dependencies declared in project ':api'.
webapp:dependencies - Displays all dependencies declared in project ':webapp'.
dependencyInsight - Displays the insight into a specific dependency in root project 'projectReports'.
api:dependencyInsight - Displays the insight into a specific dependency in project ':api'.
webapp:dependencyInsight - Displays the insight into a specific dependency in project ':webapp'.
help - Displays a help message.
api:help - Displays a help message.
webapp:help - Displays a help message.
model - Displays the configuration model of root project 'projectReports'. [incubating]
api:model - Displays the configuration model of project ':api'. [incubating]
webapp:model - Displays the configuration model of project ':webapp'. [incubating]
projects - Displays the sub-projects of root project 'projectReports'.
api:projects - Displays the sub-projects of project ':api'.
webapp:projects - Displays the sub-projects of project ':webapp'.
properties - Displays the properties of root project 'projectReports'.
api:properties - Displays the properties of project ':api'.
webapp:properties - Displays the properties of project ':webapp'.
tasks - Displays the tasks runnable from root project 'projectReports' (some of the displayed tasks may belong to subprojects).
api:tasks - Displays the tasks runnable from project ':api'.
webapp:tasks - Displays the tasks runnable from project ':webapp'.

4.7.3. Show task usage details

Running gradle help --task someTask gives you detailed information about a specific task or multiple tasks matching the given task name in your multiproject build. Below is an example of this detailed information:

Example 4.13. Obtaining detailed help for tasks

Output of gradle -q help --task libs

> gradle -q help --task libs
Detailed task information for libs

Paths
     :api:libs
     :webapp:libs

Type
     Task (org.gradle.api.Task)

Description
     Builds the JAR

Group
     build

This information includes the full task path, the task type, possible commandline options and the description of the given task.

4.7.4. Listing project dependencies

Running gradle dependencies gives you a list of the dependencies of the selected project, broken down by configuration. For each configuration, the direct and transitive dependencies of that configuration are shown in a tree. Below is an example of this report:

Example 4.14. Obtaining information about dependencies

Output of gradle -q dependencies api:dependencies webapp:dependencies

> gradle -q dependencies api:dependencies webapp:dependencies

------------------------------------------------------------
Root project
------------------------------------------------------------

No configurations

------------------------------------------------------------
Project :api - The shared API for the application
------------------------------------------------------------

compile
\--- org.codehaus.groovy:groovy-all:2.4.4

testCompile
\--- junit:junit:4.12
     \--- org.hamcrest:hamcrest-core:1.3

------------------------------------------------------------
Project :webapp - The Web application implementation
------------------------------------------------------------

compile
+--- project :api
|    \--- org.codehaus.groovy:groovy-all:2.4.4
\--- commons-io:commons-io:1.2

testCompile
No dependencies

Since a dependency report can get large, it can be useful to restrict the report to a particular configuration. This is achieved with the optional --configuration parameter:

Example 4.15. Filtering dependency report by configuration

Output of gradle -q api:dependencies --configuration testCompile

> gradle -q api:dependencies --configuration testCompile

------------------------------------------------------------
Project :api - The shared API for the application
------------------------------------------------------------

testCompile
\--- junit:junit:4.12
     \--- org.hamcrest:hamcrest-core:1.3

4.7.5. Listing project buildscript dependencies

Running gradle buildEnvironment visualises the buildscript dependencies of the selected project, similarly to how gradle dependencies visualises the dependencies of the software being built.

4.7.6. Getting the insight into a particular dependency

Running gradle dependencyInsight gives you an insight into a particular dependency (or dependencies) that match specified input. Below is an example of this report:

Example 4.16. Getting the insight into a particular dependency

Output of gradle -q webapp:dependencyInsight --dependency groovy --configuration compile

> gradle -q webapp:dependencyInsight --dependency groovy --configuration compile
org.codehaus.groovy:groovy-all:2.4.4
\--- project :api
     \--- compile

This task is extremely useful for investigating the dependency resolution, finding out where certain dependencies are coming from and why certain versions are selected. For more information please see the DependencyInsightReportTask class in the API documentation.

The built-in dependencyInsight task is a part of the 'Help' tasks group. The task needs to configured with the dependency and the configuration. The report looks for the dependencies that match the specified dependency spec in the specified configuration. If Java related plugin is applied, the dependencyInsight task is pre-configured with 'compile' configuration because typically it's the compile dependencies we are interested in. You should specify the dependency you are interested in via the command line '--dependency' option. If you don't like the defaults you may select the configuration via '--configuration' option. For more information see the DependencyInsightReportTask class in the API documentation.

4.7.7. Listing project properties

Running gradle properties gives you a list of the properties of the selected project. This is a snippet from the output:

Example 4.17. Information about properties

Output of gradle -q api:properties

> gradle -q api:properties

------------------------------------------------------------
Project :api - The shared API for the application
------------------------------------------------------------

allprojects: [project ':api']
ant: org.gradle.api.internal.project.DefaultAntBuilder@12345
antBuilderFactory: org.gradle.api.internal.project.DefaultAntBuilderFactory@12345
artifacts: org.gradle.api.internal.artifacts.dsl.DefaultArtifactHandler_Decorated@12345
asDynamicObject: DynamicObject for project ':api'
baseClassLoaderScope: org.gradle.api.internal.initialization.DefaultClassLoaderScope@12345
buildDir: /home/user/gradle/samples/userguide/tutorial/projectReports/api/build
buildFile: /home/user/gradle/samples/userguide/tutorial/projectReports/api/build.gradle

4.7.8. Profiling a build

The --profile command line option will record some useful timing information while your build is running and write a report to the build/reports/profile directory. The report will be named using the time when the build was run.

This report lists summary times and details for both the configuration phase and task execution. The times for configuration and task execution are sorted with the most expensive operations first. The task execution results also indicate if any tasks were skipped (and the reason) or if tasks that were not skipped did no work.

Builds which utilize a buildSrc directory will generate a second profile report for buildSrc in the buildSrc/build directory.

4.8. Dry Run

Sometimes you are interested in which tasks are executed in which order for a given set of tasks specified on the command line, but you don't want the tasks to be executed. You can use the -m option for this. For example, if you run “gradle -m clean compile”, you'll see all the tasks that would be executed as part of the clean and compile tasks. This is complementary to the tasks task, which shows you the tasks which are available for execution.

4.9. Summary

In this chapter, you have seen some of the things you can do with Gradle from the command-line. You can find out more about the gradle command in Appendix D, Gradle Command Line.

Chapter 5. The Gradle Wrapper

Most tools require installation on your computer before you can use them. If the installation is easy, you may think that’s fine. But it can be an unnecessary burden on the users of the build. Equally importantly, will the user install the right version of the tool for the build? What if they’re building an old version of the software?

The Gradle Wrapper (henceforth referred to as the “Wrapper”) solves both these problems and is the preferred way of starting a Gradle build.

5.1. Executing a build with the Wrapper

If a Gradle project has set up the Wrapper (and we recommend all projects do so), you can execute the build using one of the following commands from the root of the project:

  • ./gradlew <task> (on Unix-like platforms such as Linux and Mac OS X)

  • gradlew <task> (on Windows using the gradlew.bat batch file)

Each Wrapper is tied to a specific version of Gradle, so when you first run one of the commands above for a given Gradle version, it will download the corresponding Gradle distribution and use it to execute the build.

IDEs

When importing a Gradle project via its wrapper, your IDE may ask to use the Gradle 'all' distribution. This is perfectly fine and helps the IDE provide code completion for the build files.

Not only does this mean that you don’t have to manually install Gradle yourself, but you are also sure to use the version of Gradle that the build is designed for. This makes your historical builds more reliable. Just use the appropriate syntax from above whenever you see a command line starting with gradle ... in the user guide, on Stack Overflow, in articles or wherever.

For completeness sake, and to ensure you don’t delete any important files, here are the files and directories in a Gradle project that make up the Wrapper:

  • gradlew (Unix Shell script)

  • gradlew.bat (Windows batch file)

  • gradle/wrapper/gradle-wrapper.jar (Wrapper JAR)

  • gradle/wrapper/gradle-wrapper.properties (Wrapper properties)

If you’re wondering where the Gradle distributions are stored, you’ll find them in your user home directory under $USER_HOME/.gradle/wrapper/dists.

5.2. Adding the Wrapper to a project

The Wrapper is something you should check into version control. By distributing the Wrapper with your project, anyone can work with it without needing to install Gradle beforehand. Even better, users of the build are guaranteed to use the version of Gradle that the build was designed to work with. Of course, this is also great for continuous integration servers (i.e. servers that regularly build your project) as it requires no configuration on the server.

You install the Wrapper into your project by running the wrapper task. (This task is always available, even if you don't add it to your build). To specify a Gradle version use --gradle-version on the command-line. You can also set the URL to download Gradle from directly via --gradle-distribution-url. If no version or distribution URL is specified, the Wrapper will be configured to use the gradle version the wrapper task is executed with. So if you run the wrapper task with Gradle 2.4, then the Wrapper configuration will default to version 2.4.

Example 5.1. Running the Wrapper task

Output of gradle wrapper --gradle-version 2.0

> gradle wrapper --gradle-version 2.0
:wrapper

BUILD SUCCESSFUL

Total time: 1 secs

The Wrapper can be further customized by adding and configuring a Wrapper task in your build script, and then executing it.

Example 5.2. Wrapper task

build.gradle

task wrapper(type: Wrapper) {
    gradleVersion = '2.0'
}

After such an execution you find the following new or updated files in your project directory (in case the default configuration of the Wrapper task is used).

Example 5.3. Wrapper generated files

Build layout

simple/
  gradlew
  gradlew.bat
  gradle/wrapper/
    gradle-wrapper.jar
    gradle-wrapper.properties

All of these files should be submitted to your version control system. This only needs to be done once. After these files have been added to the project, the project should then be built with the added gradlew command. The gradlew command can be used exactly the same way as the gradle command.

If you want to switch to a new version of Gradle you don't need to rerun the wrapper task. It is good enough to change the respective entry in the gradle-wrapper.properties file, but if you want to take advantage of new functionality in the Gradle wrapper, then you would need to regenerate the wrapper files.

5.3. Configuration

If you run Gradle with gradlew, the Wrapper checks if a Gradle distribution for the Wrapper is available. If so, it delegates to the gradle command of this distribution with all the arguments passed originally to the gradlew command. If it didn't find a Gradle distribution, it will download it first.

When you configure the Wrapper task, you can specify the Gradle version you wish to use. The gradlew command will download the appropriate distribution from the Gradle repository. Alternatively, you can specify the download URL of the Gradle distribution. The gradlew command will use this URL to download the distribution. If you specified neither a Gradle version nor download URL, the gradlew command will download whichever version of Gradle was used to generate the Wrapper files.

For the details on how to configure the Wrapper, see the Wrapper class in the API documentation.

If you don't want any download to happen when your project is built via gradlew, simply add the Gradle distribution zip to your version control at the location specified by your Wrapper configuration. A relative URL is supported - you can specify a distribution file relative to the location of gradle-wrapper.properties file.

If you build via the Wrapper, any existing Gradle distribution installed on the machine is ignored.

5.4. Verification of downloaded Gradle distributions

The Gradle Wrapper allows for verification of the downloaded Gradle distribution via SHA-256 hash sum comparison. This increases security against targeted attacks by preventing a man-in-the-middle attacker from tampering with the downloaded Gradle distribution.

To enable this feature you'll want to first calculate the SHA-256 hash of a known Gradle distribution. You can generate a SHA-256 hash from Linux and OSX or Windows (via Cygwin) with the shasum command.

Example 5.4. Generating a SHA-256 hash

> shasum -a 256 gradle-2.4-all.zip
371cb9fbebbe9880d147f59bab36d61eee122854ef8c9ee1ecf12b82368bcf10  gradle-2.4-all.zip

Add the returned hash sum to the gradle-wrapper.properties using the distributionSha256Sum property.

Example 5.5. Configuring SHA-256 checksum verification

gradle-wrapper.properties

distributionSha256Sum=371cb9fbebbe9880d147f59bab36d61eee122854ef8c9ee1ecf12b82368bcf10

5.5. Unix file permissions

The Wrapper task adds appropriate file permissions to allow the execution of the gradlew *NIX command. Subversion preserves this file permission. We are not sure how other version control systems deal with this. What should always work is to execute “sh gradlew”.

Chapter 6. The Gradle Daemon

From Wikipedia…

A daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user.

Gradle runs on the Java Virtual Machine (JVM) and uses several supporting libraries that require a non-trivial initialization time. As a result, it can sometimes seem a little slow to start. The solution to this problem is the Gradle Daemon: a long-lived background process that executes your builds much more quickly than would otherwise be the case. We accomplish this by avoiding the expensive bootstrapping process as well as leveraging caching, by keeping data about your project in memory. Running Gradle builds with the Daemon is no different than without. Simply configure whether you want to use it or not - everything else is handled transparently by Gradle.

6.1. Enabling the Daemon

The Gradle Daemon is not enabled by default, but we do recommend always enabling it for developers’ machines (but leaving it disabled for continuous integration servers). There are several ways to enable the Daemon, but the most common one is to add the line

org.gradle.daemon=true

to the file «USER_HOME»/.gradle/gradle.properties, where «USER_HOME» is your home directory. That’s typically one of the following, depending on your platform:

  • C:\Users\<username> (Windows Vista & 7+)

  • /Users/<username> (Mac OS X)

  • /home/<username> (Linux)

If that file doesn’t exist, just create it using a text editor. You can find details of other ways to enable (and disable) the Daemon in the FAQ further down. That section also contains more detailed information on how the Daemon works.

Once you have globally enabled the Daemon in this way, all your builds will take advantage of the speed boost, regardless of the version of Gradle a particular build uses.

Continuous integration

At the moment, we recommend that you leave the Daemon disabled for continuous integration servers as using a fresh runtime for each build is more reliable since the runtime is completely isolated from previously builds. Additionally, since the Daemon primarily acts to reduce build startup times, this isn't as critical in CI as it is on a developer's machine.

6.2. Stopping an existing Daemon

As mentioned, the Daemon is a background process. You needn’t worry about a build up of Gradle processes on your machine, though: every Daemon stops after 3 hours of inactivity. If you want to explicitly stop a Daemon process for any reason, just use the command gradle --stop.

This will terminate all Daemon processes that were started with the same version of Gradle used to execute the command. If you have the Java Development Kit (JDK) installed, you can easily verify that a Daemon has stopped by running the jps command. You’ll see any running Daemons listed with the name GradleDaemon.

6.3. FAQ

6.3.1. What ways are there to enable the Gradle Daemon?

There are two recommended ways to enable the Daemon persistently for an environment:

  • Via environment variables - add the flag -Dorg.gradle.daemon=true to the GRADLE_OPTS environment variable

    Via properties file - add org.gradle.daemon=true to the «GRADLE_USER_HOME»/gradle.properties file

Note, «GRADLE_USER_HOME» defaults to «USER_HOME»/.gradle, where «USER_HOME» is the home directory of the current user. This location can be configured via the -g and --gradle-user-home command line switches, as well as by the GRADLE_USER_HOME environment variable and org.gradle.user.home JVM system property.

Both approaches have the same effect. Which one to use is up to personal preference. Most Gradle users choose the second option and add the entry to the user gradle.properties file.

On Windows, this command will enable the Daemon for the current user:

(if not exist "%USERPROFILE%/.gradle" mkdir "%USERPROFILE%/.gradle") && (echo org.gradle.daemon=true >> "%USERPROFILE%/.gradle/gradle.properties")

On UNIX-like operating systems, the following Bash shell command will enable the Daemon for the current user:

touch ~/.gradle/gradle.properties && echo "org.gradle.daemon=true" >> ~/.gradle/gradle.properties

Once the Daemon is enabled for a build environment in this way, all builds will implicitly use a Daemon.

The --daemon and --no-daemon command line switches enable and disable usage of the Daemon for individual build invocations when using the Gradle command line interface. Typically, it is more convenient to enable the Daemon for an environment (e.g. a user account) so that all builds use the Daemon without requiring to remember to supply the --daemon switch.

6.3.2. How do I disable the Gradle Daemon?

The Gradle Daemon is not enabled by default. However, once it is enabled it is sometimes desirable to disable for some projects or for some build invocations.

The --no-daemon command line switch can be used to force that a Daemon not be used for that build. This is rarely used, but can sometimes be useful when debugging issues with certain builds or Gradle plugins. This command line switch has the highest precedence when considering the build environment.

6.3.3. How do I suppress the “please consider using the Gradle Daemon” message?

Gradle may emit a warning at the end of the build suggesting that you use the Gradle Daemon. To avoid this warning you can enable the Daemon via the methods above, or explicitly disable the Daemon. You can explicitly disable the Daemon by using the --no-daemon command line switch as described above, or use one of the methods for enabling the Daemon mentioned above but using a value of false for the org.gradle.daemon property instead of true.

As it is not recommend to use the Daemon for Continuous Integration builds, Gradle will not emit the message if the CI environment variable is present.

6.3.4. Why is there more than one Daemon process on my machine?

There are several reasons why Gradle will create a new Daemon, instead of using one that is already running. The basic rule is that Gradle will start a new Daemon if there are no existing idle or compatible Daemons available. Gradle will kill any Daemon that has been idle for 3 hours or more, so you don't have to worry about cleaning them up manually.

idle

An idle Daemon is one that is not currently executing a build or doing other useful work.

compatible

A compatible Daemon is one that can (or can be made to) meet the requirements of the requested build environment. The Java runtime used to execute the build is an example aspect of the build environment. Another example is the set of JVM system properties required by the build runtime.

Some aspects of the requested build environment may not be met by an Daemon. If the Daemon is running with a Java 7 runtime, but the requested environment calls for Java 8 then the Daemon is not compatible and another must be started. Moreover, certain properties of a Java runtime cannot be changed once the JVM has started. It is not possible to change the memory allocation (e.g. -Xmx1024m), default text encoding, default locale, etc of a running JVM.

The “requested build environment” is typically constructed implicitly from aspects of the build client’s (e.g. Gradle command line client, IDE etc.) environment and explicitly via command line switches and settings. See Chapter 11, The Build Environment for details on how to specify and control the build environment.

The following JVM system properties are effectively immutable. If the requested build environment requires any of these properties, with a different value than a Daemon’s JVM has for this property, the Daemon is not compatible.

  • file.encoding
  • user.language
  • user.country
  • user.variant
  • java.io.tmpdir
  • javax.net.ssl.keyStore
  • javax.net.ssl.keyStorePassword
  • javax.net.ssl.keyStoreType
  • javax.net.ssl.trustStore
  • javax.net.ssl.trustStorePassword
  • javax.net.ssl.trustStoreType
  • com.sun.management.jmxremote

The following JVM attributes, controlled by startup arguments, are also effectively immutable. The corresponding attributes of the requested build environment and the Daemon’s environment must match exactly in order for a Daemon to be compatible.

  • The maximum heap size (i.e. the -Xmx JVM argument)
  • The minimum heap size (i.e. the -Xms JVM argument)
  • The boot classpath (i.e. the -Xbootclasspath argument)
  • The “assertion” status (i.e. the -ea argument)

The required Gradle version is another aspect of the requested build environment. Daemon processes are coupled to a specific Gradle runtime. Working on multiple Gradle projects during a session that use different Gradle versions is a common reason for having more than one running Daemon process.

6.3.5. How much memory does the Daemon use and can I give it more?

If the requested build environment does not specify a maximum heap size, the Daemon will use up to 1GB of heap. It will use your the JVM's default minimum heap size. 1GB is more than enough for most builds. Larger builds with hundreds of subprojects, lots of configuration, and source code may require, or perform better, with more memory.

To increase the amount of memory the Daemon can use, specify the appropriate flags as part of the requested build environment. Please see Chapter 11, The Build Environment for details.

6.3.6. How can I stop a Daemon?

Daemon processes will automatically terminate themselves after 3 hours of inactivity. If you wish to stop a Daemon process before this, you can either kill the process via your operating system or run the gradle --stop command. The --stop switch causes Gradle to request that all running Daemon processes, of the same Gradle version used to run the command, terminate themselves.

6.3.7. What can go wrong with Daemon?

Considerable engineering effort has gone into making the Daemon robust, transparent and unobtrusive during day to day development. However, Daemon processes can occasionally be corrupted or exhausted. A Gradle build executes arbitrary code from multiple sources. While Gradle itself is designed for and heavily tested with the Daemon, user build scripts and third party plugins can destabilize the Daemon process through defects such as memory leaks or global state corruption.

It is also possible to destabilize the Daemon (and build environment in general) by running builds that do not release resources correctly. This is a particularly poignant problem when using Microsoft Windows as it is less forgiving of programs that fail to close files after reading or writing.

Gradle actively monitors heap usage and attempts to detect when a leak is starting to exhaust the available heap space in the daemon. When it detects a problem with heap space, the Gradle daemon will finish the currently running build and restart the daemon on the next build. This monitoring is enabled by default, but can be disabled by setting the org.gradle.daemon.performance.enable-monitoring system property to false.

If it is suspected that the Daemon process has become unstable, it can simply be killed. Recall that the --no-daemon switch can be specified for a build to prevent use of the Daemon. This can be useful to diagnose whether or not the Daemon is actually the culprit of a problem.

6.4. When should I not use the Gradle Daemon?

It is recommended that the Daemon is used in all developer environments. It is recommend to not enable the Daemon for Continuous Integration and build server environments.

The Daemon enables faster builds, which is particularly important when a human is sitting in front of the build. For CI builds, stability and predictability is of utmost importance. Using a fresh runtime (i.e. process) for each build is more reliable as the runtime is completely isolated from previous builds.

6.5. Tools & IDEs

The Gradle Tooling API (see Chapter 13, Embedding Gradle using the Tooling API), that is used by IDEs and other tools to integrate with Gradle, always use the Gradle Daemon to execute builds. If you are executing Gradle builds from within you're IDE you are using the Gradle Daemon and do not need to enable it for your environment.

However, unless you have explicitly enabled the Gradle Daemon for you environment your builds from the command line will not use the Gradle Daemon.

6.6. How does the Gradle Daemon make builds faster?

The Gradle Daemon is a long lived build process. In between builds it waits idly for the next build. This has the obvious benefit of only requiring Gradle to be loaded into memory once for multiple builds, as opposed to once for each build. This in itself is a significant performance optimization, but that's not where it stops.

A significant part of the story for modern JVM performance is runtime code optimization. For example, HotSpot (the JVM implementation provided by Oracle and used as the basis of OpenJDK) applies optimization to code while it is running. The optimization is progressive and not instantaneous. That is, the code is progressively optimized during execution which means that subsequent builds can be faster purely due to this optimization process. Experiments with HotSpot have shown that it takes somewhere between 5 and 10 builds for optimization to stabilize. The difference in perceived build time between the first build and the 10th for a Daemon can be quite dramatic.

The Daemon also allows more effective in memory caching across builds. For example, the classes needed by the build (e.g. plugins, build scripts) can be held in memory between builds. Similarly, Gradle can maintain in-memory caches of build data such as the hashes of task inputs and outputs, used for incremental building.

6.6.1. Potential future enhancements

Currently, the Daemon makes builds faster by effectively supporting in memory caching and by the JVM optimizer making the code faster. In future Gradle versions, the Daemon will become even smarter and perform work preemptively. It could, for example, start downloading dependencies immediately after the build script has been edited under the assumption that the build is about to be run and the newly changed or added dependencies will be required.

There are many other ways in that the Gradle Daemon will enable even faster builds in future Gradle versions.

Chapter 7. Dependency Management Basics

This chapter introduces some of the basics of dependency management in Gradle.

7.1. What is dependency management?

Very roughly, dependency management is made up of two pieces. Firstly, Gradle needs to know about the things that your project needs to build or run, in order to find them. We call these incoming files the dependencies of the project. Secondly, Gradle needs to build and upload the things that your project produces. We call these outgoing files the publications of the project. Let's look at these two pieces in more detail:

Most projects are not completely self-contained. They need files built by other projects in order to be compiled or tested and so on. For example, in order to use Hibernate in my project, I need to include some Hibernate jars in the classpath when I compile my source. To run my tests, I might also need to include some additional jars in the test classpath, such as a particular JDBC driver or the Ehcache jars.

These incoming files form the dependencies of the project. Gradle allows you to tell it what the dependencies of your project are, so that it can take care of finding these dependencies, and making them available in your build. The dependencies might need to be downloaded from a remote Maven or Ivy repository, or located in a local directory, or may need to be built by another project in the same multi-project build. We call this process dependency resolution.

Note that this feature provides a major advantage over Ant. With Ant, you only have the ability to specify absolute or relative paths to specific jars to load. With Gradle, you simply declare the “names” of your dependencies, and other layers determine where to get those dependencies from. You can get similar behavior from Ant by adding Apache Ivy, but Gradle does it better.

Often, the dependencies of a project will themselves have dependencies. For example, Hibernate core requires several other libraries to be present on the classpath with it runs. So, when Gradle runs the tests for your project, it also needs to find these dependencies and make them available. We call these transitive dependencies.

The main purpose of most projects is to build some files that are to be used outside the project. For example, if your project produces a Java library, you need to build a jar, and maybe a source jar and some documentation, and publish them somewhere.

These outgoing files form the publications of the project. Gradle also takes care of this important work for you. You declare the publications of your project, and Gradle take care of building them and publishing them somewhere. Exactly what “publishing” means depends on what you want to do. You might want to copy the files to a local directory, or upload them to a remote Maven or Ivy repository. Or you might use the files in another project in the same multi-project build. We call this process publication.

7.2. Declaring your dependencies

Let's look at some dependency declarations. Here's a basic build script:

Example 7.1. Declaring dependencies

build.gradle

apply plugin: 'java'

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'org.hibernate', name: 'hibernate-core', version: '3.6.7.Final'
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

What's going on here? This build script says a few things about the project. Firstly, it states that Hibernate core 3.6.7.Final is required to compile the project's production source. By implication, Hibernate core and its dependencies are also required at runtime. The build script also states that any junit >= 4.0 is required to compile the project's tests. It also tells Gradle to look in the Maven central repository for any dependencies that are required. The following sections go into the details.

7.3. Dependency configurations

In Gradle dependencies are grouped into configurations. A configuration is simply a named set of dependencies. We will refer to them as dependency configurations. You can use them to declare the external dependencies of your project. As we will see later, they are also used to declare the publications of your project.

The Java plugin defines a number of standard configurations. These configurations represent the classpaths that the Java plugin uses. Some are listed below, and you can find more details in Table 45.5, “Java plugin - dependency configurations”.

compile

The dependencies required to compile the production source of the project.

runtime

The dependencies required by the production classes at runtime. By default, also includes the compile time dependencies.

testCompile

The dependencies required to compile the test source of the project. By default, also includes the compiled production classes and the compile time dependencies.

testRuntime

The dependencies required to run the tests. By default, also includes the compile, runtime and test compile dependencies.

Various plugins add further standard configurations. You can also define your own custom configurations to use in your build. Please see Section 23.3, “Dependency configurations” for the details of defining and customizing dependency configurations.

7.4. External dependencies

There are various types of dependencies that you can declare. One such type is an external dependency. This is a dependency on some files built outside the current build, and stored in a repository of some kind, such as Maven central, or a corporate Maven or Ivy repository, or a directory in the local file system.

To define an external dependency, you add it to a dependency configuration:

Example 7.2. Definition of an external dependency

build.gradle

dependencies {
    compile group: 'org.hibernate', name: 'hibernate-core', version: '3.6.7.Final'
}

An external dependency is identified using group, name and version attributes. Depending on which kind of repository you are using, group and version may be optional.

The shortcut form for declaring external dependencies looks like “group:name:version”.

Example 7.3. Shortcut definition of an external dependency

build.gradle

dependencies {
    compile 'org.hibernate:hibernate-core:3.6.7.Final'
}

To find out more about defining and working with dependencies, have a look at Section 23.4, “How to declare your dependencies”.

7.5. Repositories

How does Gradle find the files for external dependencies? Gradle looks for them in a repository. A repository is really just a collection of files, organized by group, name and version. Gradle understands several different repository formats, such as Maven and Ivy, and several different ways of accessing the repository, such as using the local file system or HTTP.

By default, Gradle does not define any repositories. You need to define at least one before you can use external dependencies. One option is use the Maven central repository:

Example 7.4. Usage of Maven central repository

build.gradle

repositories {
    mavenCentral()
}

Or Bintray's JCenter:

Example 7.5. Usage of JCenter repository

build.gradle

repositories {
    jcenter()
}

Or a any other remote Maven repository:

Example 7.6. Usage of a remote Maven repository

build.gradle

repositories {
    maven {
        url "http://repo.mycompany.com/maven2"
    }
}

Or a remote Ivy repository:

Example 7.7. Usage of a remote Ivy directory

build.gradle

repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
    }
}

You can also have repositories on the local file system. This works for both Maven and Ivy repositories.

Example 7.8. Usage of a local Ivy directory

build.gradle

repositories {
    ivy {
        // URL can refer to a local directory
        url "../local-repo"
    }
}

A project can have multiple repositories. Gradle will look for a dependency in each repository in the order they are specified, stopping at the first repository that contains the requested module.

To find out more about defining and working with repositories, have a look at Section 23.6, “Repositories”.

7.6. Publishing artifacts

Dependency configurations are also used to publish files.[2] We call these files publication artifacts, or usually just artifacts.

The plugins do a pretty good job of defining the artifacts of a project, so you usually don't need to do anything special to tell Gradle what needs to be published. However, you do need to tell Gradle where to publish the artifacts. You do this by attaching repositories to the uploadArchives task. Here's an example of publishing to a remote Ivy repository:

Example 7.9. Publishing to an Ivy repository

build.gradle

uploadArchives {
    repositories {
        ivy {
            credentials {
                username "username"
                password "pw"
            }
            url "http://repo.mycompany.com"
        }
    }
}

Now, when you run gradle uploadArchives, Gradle will build and upload your Jar. Gradle will also generate and upload an ivy.xml as well.

You can also publish to Maven repositories. The syntax is slightly different.[3] Note that you also need to apply the Maven plugin in order to publish to a Maven repository. when this is in place, Gradle will generate and upload a pom.xml.

Example 7.10. Publishing to a Maven repository

build.gradle

apply plugin: 'maven'

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://localhost/tmp/myRepo/")
        }
    }
}

To find out more about publication, have a look at Chapter 30, Publishing artifacts.

7.7. Where to next?

For all the details of dependency resolution, see Chapter 23, Dependency Management, and for artifact publication see Chapter 30, Publishing artifacts.

If you are interested in the DSL elements mentioned here, have a look at Project.configurations{}, Project.repositories{} and Project.dependencies{}.

Otherwise, continue on to some of the other tutorials.



[2] We think this is confusing, and we are gradually teasing apart the two concepts in the Gradle DSL.

[3] We are working to make the syntax consistent for resolving from and publishing to Maven repositories.

Chapter 8. Introduction to multi-project builds

Only the smallest of projects has a single build file and source tree, unless it happens to be a massive, monolithic application. It’s often much easier to digest and understand a project that has been split into smaller, inter-dependent modules. The word “inter-dependent” is important, though, and is why you typically want to link the modules together through a single build.

Gradle supports this scenario through multi-project builds.

8.1. Structure of a multi-project build

Such builds come in all shapes and sizes, but they do have some common characteristics:

  • A settings.gradle file in the root or master directory of the project

  • A build.gradle file in the root or master directory

  • Child directories that have their own *.gradle build files (some multi-project builds may omit child project build scripts)

The settings.gradle file tells Gradle how the project and subprojects are structured. Fortunately, you don’t have to read this file simply to learn what the project structure is as you can run the command gradle projects. Here's the output from using that command on the Java multiproject build in the Gradle samples:

Example 8.1. Listing the projects in a build

Output of gradle -q projects

> gradle -q projects

------------------------------------------------------------
Root project
------------------------------------------------------------

Root project 'multiproject'
+--- Project ':api'
+--- Project ':services'
|    +--- Project ':services:shared'
|    \--- Project ':services:webservice'
\--- Project ':shared'

To see a list of the tasks of a project, run gradle <project-path>:tasks
For example, try running gradle :api:tasks


This tells you that multiproject has three immediate child projects: api, services and shared. The services project then has its own children, shared and webservice. These map to the directory structure, so it’s easy to find them. For example, you can find webservice in <root>/services/webservice.

By default, Gradle uses the name of the directory it finds the settings.gradle as the name of the root project. This usually doesn't cause problems since all developers check out the same directory name when working on a project. On Continuous Integration servers, like Jenkins, the directory name may be auto-generated and not match the name in your VCS. For that reason, it's recommended that you always set the root project name to something predictable, even in single project builds. You can configure the root project name by setting rootProject.name.

Each project will usually have its own build file, but that's not necessarily the case. In the above example, the services project is just a container or grouping of other subprojects. There is no build file in the corresponding directory. However, multiproject does have one for the root project.

The root build.gradle is often used to share common configuration between the child projects, for example by applying the same sets of plugins and dependencies to all the child projects. It can also be used to configure individual subprojects when it is preferable to have all the configuration in one place. This means you should always check the root build file when discovering how a particular subproject is being configured.

Another thing to bear in mind is that the build files might not be called build.gradle. Many projects will name the build files after the subproject names, such as api.gradle and services.gradle from the previous example. Such an approach helps a lot in IDEs because it’s tough to work out which build.gradle file out of twenty possibilities is the one you want to open. This little piece of magic is handled by the settings.gradle file, but as a build user you don’t need to know the details of how it’s done. Just have a look through the child project directories to find the files with the .gradle suffix.

Once you know what subprojects are available, the key question for a build user is how to execute the tasks within the project.

8.2. Executing a multi-project build

From a user's perspective, multi-project builds are still collections of tasks you can run. The difference is that you may want to control which project's tasks get executed. You have two options here:

  • Change to the directory corresponding to the subproject you’re interested in and just execute gradle <task> as normal.

  • Use a qualified task name from any directory, although this is usually done from the root. For example: gradle :services:webservice:build will build the webservice subproject and any subprojects it depends on.

The first approach is similar to the single-project use case, but Gradle works slightly differently in the case of a multi-project build. The command gradle test will execute the test task in any subprojects, relative to the current working directory, that have that task. So if you run the command from the root project directory, you’ll run test in api, shared, services:shared and services:webservice. If you run the command from the services project directory, you’ll only execute the task in services:shared and services:webservice.

For more control over what gets executed, use qualified names (the second approach mentioned). These are paths just like directory paths, but use ‘:’ instead of ‘/’ or ‘\’. If the path begins with a ‘:’, then the path is resolved relative to the root project. In other words, the leading ‘:’ represents the root project itself. All other colons are path separators.

This approach works for any task, so if you want to know what tasks are in a particular subproject, just use the tasks task, e.g. gradle :services:webservice:tasks .

Regardless of which technique you use to execute tasks, Gradle will take care of building any subprojects that the target depends on. You don’t have to worry about the inter-project dependencies yourself. If you’re interested in how this is configured, you can read about writing multi-project builds later in the user guide.

There’s one last thing to note. When you’re using the Gradle wrapper, the first approach doesn’t work well because you have to specify the path to the wrapper script if you’re not in the project root. For example, if you’re in the webservice subproject directory, you would have to run ../../gradlew build.

That’s all you really need to know about multi-project builds as a build user. You can now identify whether a build is a multi-project one and you can discover its structure. And finally, you can execute tasks within specific subprojects.

Chapter 9. Continuous build

Continuous build is an incubating feature. This means that it is incomplete and not yet at regular Gradle production quality. This also means that this Gradle User Guide chapter is a work in progress.

Typically, you ask Gradle to perform a single build by way of specifying tasks that Gradle should execute. Gradle will determine the the actual set of tasks that need to be executed to satisfy the request, execute them all, and then stop doing work until the next request. A continuous build differs in that Gradle will keep satisfying the initial build request (until instructed to stop) by executing the build when it is detected that the result of the previous build is now out of date. For example, if your build compiles Java source files to Java class files, a continuous build would automatically initiate a compile when the source files change. Continuous build is useful for many scenarios.

9.1. How do I start and stop a continuous build?

A continuous build can be started by supplying either the --continuous or -t switches to Gradle, along with the list of tasks, switches and arguments that define the work to do. For example, gradle build --continuous. This will have the same effect as running gradle build, but instead of Gradle exiting when done, it will wait for changes to the build inputs. When a change occurs, gradle build will be automatically executed again and the process repeats.

If Gradle is attached to an interactive input source, such as a terminal, the continuous build can be exited by pressing CTRL-D (On Microsoft Windows, it is required to also press ENTER or RETURN after CTRL-D). If Gradle is not attached to an interactive input source (e.g. is running as part of a script), the build process must be terminated (e.g. using the kill command or similar). If the build is being executed via the Tooling API, the build can be cancelled using the Tooling API's cancellation mechanism.

9.2. What will cause a subsequent build?

Task file inputs

Task implementations declare their file system inputs by annotating their properties with InputFiles and other similar annotations. Please see Example 17.24, “Declaring the inputs and outputs of a task” for more information.

At this time, only changes to task inputs are noticed. Gradle will start watching for changes just before the task starts to execute. No other changes will initiate a build. For example, changes to build scripts and build logic will not initiate build. Likewise, changes to files that are read during the configuration of the build, not the execution, will not initiate a build. In order to incorporate such changes, the continuous build must be restarted manually.

Consider a typical build using the Java plugin, using the conventional filesystem layout. The following diagram visualizes the task graph for gradle build:

Figure 9.1. Java plugin task graph

Java plugin task graph

The following key tasks of the graph use files in the corresponding directories as inputs:

compileJava
src/main/java
processResources
src/main/resources
compileTestJava
src/test/java
processTestResources
src/test/resources

Assuming that the initial build is successful (i.e. the build task and its dependencies complete without error), changes to files in, or the addition/remove of files from, the locations listed above will initiate a new build. If a change is made to a Java source file in src/main/java, the build will fire and all tasks will be scheduled. Gradle's incremental build support ensures that only the tasks that are actually affected by the change are executed.

If the change to the main Java source causes compilation to fail, subsequent changes to the test source in src/test/java will not initiate a new build. As the test source depends on the main source, there is no point building until the main source has changed, potentially fixing the compilation error. After each build, only the inputs of the tasks that actually executed will be monitored for changes.

Continuous build is in no way coupled to compilation. It works for all types of tasks. For example, the processResources task copies and processes the files from src/main/resources for inclusion in the built JAR. As such, a change to any file in this directory will also initiate a build.

9.3. Limitations and quirks

There are several issues to be aware with the current implementation of continuous build. These are likely to be addressed in future Gradle releases.

9.3.1. Build cycles

Gradle starts watching for changes just before a task executes. If a task modifies its own inputs while executing, Gradle will detect the change and trigger a new build. If every time the task executes, the inputs are modified again, the build will be triggered again. This isn't unique to continuous build. A task that modifies its own inputs will never be considered up-to-date when run "normally" without continuous build.

If your build enters a build cycle like this, you can track down the task by looking at the list of files reported changed by Gradle. After identifying the file(s) that are changed during each build, you should look for a task that has that file as an input. In some cases, it may be obvious (e.g., a Java file is compiled with compileJava). In other cases, you can use --info logging to find the task that is out-of-date due to the identified files.

9.3.2. Requires Java 7 or later

Gradle uses the JDK's WatchService to receive notification of changes to files between builds. This API was introduced in Java 7. As such, Gradle's continuous build is not currently supported when building with Java 6.

9.3.3. Performance and stability

The JDK file watching facility relies on inefficient file system polling on Mac OS X (see: JDK-7133447). This can significantly delay notification of changes on large projects with many source files.

Additionally, the watching mechanism may deadlock under heavy load on Mac OS X (see: JDK-8079620). This will manifest as Gradle appearing not to notice file changes. If you suspect this is occurring, exit continuous build and start again.

On Linux, OpenJDK's implementation of the file watch service can sometimes miss file system events (see: JDK-8145981).

9.3.4. Changes to symbolic links

  • Creating or removing symbolic link to files will initiate a build.

  • Modifying the target of a symbolic link will not cause a rebuild.

  • Creating or removing symbolic links to directories will not cause rebuilds.

  • Creating new files in the target directory of a symbolic link will not cause a rebuild.

  • Deleting the target directory will not cause a rebuild.

9.3.5. Changes to build logic are not considered

The current implementation does not recalculate the build model on subsequent builds. This means that changes to task configuration, or any other change to the build model, are effectively ignored.

Chapter 10. Using the Gradle Graphical User Interface

In addition to supporting a traditional command line interface, Gradle offers a graphical user interface. This is a stand alone user interface that can be launched with the --gui option.

Example 10.1. Launching the GUI

gradle --gui

Note that this command blocks until the Gradle GUI is closed. Under *nix it is probably preferable to run this as a background task (gradle --gui&)

If you run this from your Gradle project working directory, you should see a tree of tasks.

Figure 10.1. GUI Task Tree

GUI Task Tree

It is preferable to run this command from your Gradle project directory so that the settings of the UI will be stored in your project directory. However, you can run it then change the working directory via the Setup tab in the UI.

The UI displays 4 tabs along the top and an output window along the bottom.

10.1. Task Tree

The Task Tree shows a hierarchical display of all projects and their tasks. Double clicking a task executes it.

There is also a filter so that uncommon tasks can be hidden. You can toggle the filter via the Filter button. Editing the filter allows you to configure which tasks and projects are shown. Hidden tasks show up in red. Note: newly created tasks will show up by default (versus being hidden by default).

The Task Tree context menu provides the following options:

  • Execute ignoring dependencies. This does not require dependent projects to be rebuilt (same as the -a option).

  • Add tasks to the favorites (see Favorites tab)

  • Hide the selected tasks. This adds them to the filter.

  • Edit the build.gradle file. Note: this requires Java 1.6 or higher and requires that you have .gradle files associated in your OS.

10.2. Favorites

The Favorites tab is a good place to store commonly-executed commands. These can be complex commands (anything that's legal to Gradle) and you can provide them with a display name. This is useful for creating, say, a custom build command that explicitly skips tests, documentation, and samples that you could call “fast build”.

You can reorder favorites to your liking and even export them to disk so they can imported by others. If you edit them, you are given options to “Always Show Live Output”. This only applies if you have “Only Show Output When Errors Occur”. This override always forces the output to be shown.

10.3. Command Line

The Command Line tab is where you can execute a single Gradle command directly. Just enter whatever you would normally enter after 'gradle' on the command line. This also provides a place to try out commands before adding them to favorites.

10.4. Setup

The Setup tab allows configuration of some general settings.

Figure 10.2. GUI Setup

GUI Setup

  • Current Directory

    Defines the root directory of your Gradle project (typically where build.gradle is located).

  • Stack Trace Output

    This determines how much information to write out in stack traces when errors occur. Note: if you specify a stack trace level on either the Command Line or Favorites tab, it will override this stack trace level.

  • Only Show Output When Errors Occur

    Enabling this option hides any output when a task is executed unless the build fails.

  • Use Custom Gradle Executor - Advanced feature

    This provides you with an alternate way to launch Gradle commands. This is useful if your project requires some extra setup that is done inside another batch file or shell script (such as specifying an init script).

Chapter 11. The Build Environment

11.1. Configuring the build environment via gradle.properties

Gradle provides several options that make it easy to configure the Java process that will be used to execute your build. While it's possible to configure these in your local environment via GRADLE_OPTS or JAVA_OPTS, certain settings like JVM memory settings, Java home, daemon on/off can be more useful if they can be versioned with the project in your VCS so that the entire team can work with a consistent environment. Setting up a consistent environment for your build is as simple as placing these settings into a gradle.properties file. The configuration is applied in following order (if an option is configured in multiple locations the last one wins):

  • from gradle.properties in project build dir.
  • from gradle.properties in gradle user home.
  • from system properties, e.g. when -Dsome.property is set on the command line.

The following properties can be used to configure the Gradle build environment:

org.gradle.daemon

When set to true the Gradle daemon is used to run the build. For local developer builds this is our favorite property. The developer environment is optimized for speed and feedback so we nearly always run Gradle jobs with the daemon. We don't run CI builds with the daemon (i.e. a long running process) as the CI environment is optimized for consistency and reliability.

org.gradle.java.home

Specifies the Java home for the Gradle build process. The value can be set to either a jdk or jre location, however, depending on what your build does, jdk is safer. A reasonable default is used if the setting is unspecified.

org.gradle.jvmargs

Specifies the jvmargs used for the daemon process. The setting is particularly useful for tweaking memory settings. At the moment the default settings are pretty generous with regards to memory.

org.gradle.configureondemand

Enables new incubating mode that makes Gradle selective when configuring projects. Only relevant projects are configured which results in faster builds for large multi-projects. See Section 24.1.1.1, “Configuration on demand”.

org.gradle.parallel

When configured, Gradle will run in incubating parallel mode.

org.gradle.workers.max

When configured, Gradle will use a maximum of the given number of workers. See --max-workers for details.

org.gradle.debug

When set to true, Gradle will run the build with remote debugging enabled, listening on port 5005. Note that this is the equivalent of adding -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005 to the JVM command line and will suspend the virtual machine until a debugger is attached.

org.gradle.daemon.performance.enable-monitoring

When set to false, Gradle will not monitor the memory usage of running daemons. See Section 6.3.7, “What can go wrong with Daemon?”.

11.1.1. Forked Java processes

Many settings (like the Java version and maximum heap size) can only be specified when launching a new JVM for the build process. This means that Gradle must launch a separate JVM process to execute the build after parsing the various gradle.properties files. When running with the daemon, a JVM with the correct parameters is started once and reused for each daemon build execution. When Gradle is executed without the daemon, then a new JVM must be launched for every build execution, unless the JVM launched by the Gradle start script happens to have the same parameters.

This launching of an extra JVM on every build execution is quite expensive, which is why if you are setting either org.gradle.java.home or org.gradle.jvmargs we highly recommend that you use the Gradle Daemon. See Chapter 6, The Gradle Daemon for more details.

11.2. Gradle properties and system properties

Gradle offers a variety of ways to add properties to your build. With the -D command line option you can pass a system property to the JVM which runs Gradle. The -D option of the gradle command has the same effect as the -D option of the java command.

You can also add properties to your project objects using properties files. You can place a gradle.properties file in the Gradle user home directory (defined by the “GRADLE_USER_HOME” environment variable, which if not set defaults to USER_HOME/.gradle) or in your project directory. For multi-project builds you can place gradle.properties files in any subproject directory. The properties set in a gradle.properties file can be accessed via the project object. The properties file in the user's home directory has precedence over property files in the project directories.

You can also add properties directly to your project object via the -P command line option.

Gradle can also set project properties when it sees specially-named system properties or environment variables. This feature is very useful when you don't have admin rights to a continuous integration server and you need to set property values that should not be easily visible, typically for security reasons. In that situation, you can't use the -P option, and you can't change the system-level configuration files. The correct strategy is to change the configuration of your continuous integration build job, adding an environment variable setting that matches an expected pattern. This won't be visible to normal users on the system. [4]

If the environment variable name looks like ORG_GRADLE_PROJECT_prop=somevalue, then Gradle will set a prop property on your project object, with the value of somevalue. Gradle also supports this for system properties, but with a different naming pattern, which looks like org.gradle.project.prop.

You can also set system properties in the gradle.properties file. If a property name in such a file has the prefix “systemProp.”, like “systemProp.propName”, then the property and its value will be set as a system property, without the prefix. In a multi project build, “systemProp.” properties set in any project except the root will be ignored. That is, only the root project's gradle.properties file will be checked for properties that begin with the “systemProp.” prefix.

Example 11.1. Setting properties with a gradle.properties file

gradle.properties

gradlePropertiesProp=gradlePropertiesValue
sysProp=shouldBeOverWrittenBySysProp
envProjectProp=shouldBeOverWrittenByEnvProp
systemProp.system=systemValue

build.gradle

task printProps << {
    println commandLineProjectProp
    println gradlePropertiesProp
    println systemProjectProp
    println envProjectProp
    println System.properties['system']
}

Output of gradle -q -PcommandLineProjectProp=commandLineProjectPropValue -Dorg.gradle.project.systemProjectProp=systemPropertyValue printProps

> gradle -q -PcommandLineProjectProp=commandLineProjectPropValue -Dorg.gradle.project.systemProjectProp=systemPropertyValue printProps
commandLineProjectPropValue
gradlePropertiesValue
systemPropertyValue
envPropertyValue
systemValue

11.2.1. Checking for project properties

You can access a project property in your build script simply by using its name as you would use a variable. If this property does not exist, an exception will be thrown and the build will fail. If your build script relies on optional properties the user might set, perhaps in a gradle.properties file, you need to check for existence before you access them. You can do this by using the method hasProperty('propertyName') which returns true or false.

11.3. Accessing the web via a proxy

Configuring an HTTP proxy (for downloading dependencies, for example) is done via standard JVM system properties. These properties can be set directly in the build script; for example, setting the proxy host would be done with System.setProperty('http.proxyHost', 'www.somehost.org'). Alternatively, the properties can be specified in a gradle.properties file, either in the build's root directory or in the Gradle home directory.

Example 11.2. Configuring an HTTP proxy

gradle.properties

systemProp.http.proxyHost=www.somehost.org
systemProp.http.proxyPort=8080
systemProp.http.proxyUser=userid
systemProp.http.proxyPassword=password
systemProp.http.nonProxyHosts=*.nonproxyrepos.com|localhost

There are separate settings for HTTPS.

Example 11.3. Configuring an HTTPS proxy

gradle.properties

systemProp.https.proxyHost=www.somehost.org
systemProp.https.proxyPort=8080
systemProp.https.proxyUser=userid
systemProp.https.proxyPassword=password
systemProp.https.nonProxyHosts=*.nonproxyrepos.com|localhost

We could not find a good overview for all possible proxy settings. One place to look are the constants in a file from the Ant project. Here's a link to the Subversion view. The other is a Networking Properties page from the JDK docs. If anyone knows of a better overview, please let us know via the mailing list.

11.3.1. NTLM Authentication

If your proxy requires NTLM authentication, you may need to provide the authentication domain as well as the username and password. There are 2 ways that you can provide the domain for authenticating to a NTLM proxy:

  • Set the http.proxyUser system property to a value like domain/username.
  • Provide the authentication domain via the http.auth.ntlm.domain system property.



[4] Jenkins, Teamcity, or Bamboo are some CI servers which offer this functionality.

Chapter 12. Troubleshooting

This chapter is currently a work in progress.

When using Gradle (or any software package), you can run into problems. You may not understand how to use a particular feature, or you may encounter a defect. Or, you may have a general question about Gradle.

This chapter gives some advice for troubleshooting problems and explains how to get help with your problems.

12.1. Working through problems

If you are encountering problems, one of the first things to try is using the very latest release of Gradle. New versions of Gradle are released frequently with bug fixes and new features. The problem you are having may have been fixed in a new release.

If you are using the Gradle Daemon, try temporarily disabling the daemon (you can pass the command line switch --no-daemon). More information about troubleshooting the daemon process is located in Chapter 6, The Gradle Daemon.

12.2. Getting help

The place to go for help with Gradle is http://forums.gradle.org. The Gradle Forums is the place where you can report problems and ask questions of the Gradle developers and other community members.

If something's not working for you, posting a question or problem report to the forums is the fastest way to get help. It's also the place to post improvement suggestions or new ideas. The development team frequently posts news items and announces releases via the forum, making it a great way to stay up to date with the latest Gradle developments.

Chapter 13. Embedding Gradle using the Tooling API

13.1. Introduction to the Tooling API

Gradle provides a programmatic API called the Tooling API, which you can use for embedding Gradle into your own software. This API allows you to execute and monitor builds and to query Gradle about the details of a build. The main audience for this API is IDE, CI server, other UI authors; however, the API is open for anyone who needs to embed Gradle in their application.

  • Gradle TestKit uses the Tooling API for functional testing of your Gradle plugins.
  • Eclipse Buildship uses the Tooling API for importing your Gradle project and running tasks.
  • IntelliJ IDEA uses the Tooling API for importing your Gradle project and running tasks.

13.2. Tooling API Features

A fundamental characteristic of the Tooling API is that it operates in a version independent way. This means that you can use the same API to work with different target versions of Gradle, including versions that are both newer and older than the version of the Tooling API that you are using. The Tooling API is Gradle wrapper aware and, by default, uses the same target Gradle version as that used by the wrapper-powered project.

Some features that the Tooling API provides:

  • Query the details of a build, including the project hierarchy and the project dependencies, external dependencies (including source and Javadoc jars), source directories and tasks of each project.
  • Execute a build and listen to stdout and stderr logging and progress messages (e.g. the messages shown in the 'status bar' when you run on the command line).
  • Execute a specific test class or test method.
  • Receive interesting events as a build executes, such as project configuration, task execution or test execution.
  • Cancel a build that is running.
  • Combine multiple separate Gradle builds into a single composite build.
  • The Tooling API can download and install the appropriate Gradle version, similar to the wrapper.
  • The implementation is lightweight, with only a small number of dependencies. It is also a well-behaved library, and makes no assumptions about your classloader structure or logging configuration. This makes the API easy to embed in your application.

13.3. Tooling API and the Gradle Build Daemon

The Tooling API always uses the Gradle daemon. This means that subsequent calls to the Tooling API, be it model building requests or task executing requests will be executed in the same long-living process. Chapter 6, The Gradle Daemon contains more details about the daemon, specifically information on situations when new daemons are forked.

13.4. Quickstart

As the Tooling API is an interface for developers, the Javadoc is the main documentation for it. We provide several samples that live in samples/toolingApi in your Gradle distribution. These samples specify all of the required dependencies for the Tooling API with examples for querying information from Gradle builds and executing tasks from the Tooling API.

The main entry point to the Tooling API is the GradleConnector. You can navigate from there to find code samples and explore the available Tooling API models. There are two ways of using the GradleConnector to connect to a Gradle build.

  • You can use GradleConnector.connect() to create a ProjectConnection. A ProjectConnection connects to a single Gradle project. Using the connection you can execute tasks, tests and retrieve models relative to this project. This is the original API provided by the Tooling API. Use this API when you wish to use a stable non-incubating API.
  • You can use GradleConnector.newGradleConnection() to create a GradleConnectionBuilder. GradleConnectionBuilder can be used to connect to any number of Gradle builds at one time. Executing tasks and retrieving models are performed in the context of the composite. Instead of retrieving a single model for a single Gradle project, the Tooling API can provide all models for all projects with a single method call. Note that this API is currently incubating and may change at any time.

13.5. Gradle and Java version compatibility

The current version of the Tooling API supports running builds using Gradle versions 1.0-milestone-8 and later. Support for versions from 1.0-milestone-8 to 1.1 is deprecated and will be removed from the Tooling API in Gradle 3.0.

You should note that not all features of the Tooling API are available for all versions of Gradle. For example, build cancellation is only available when a build uses Gradle 2.1 and later. Refer to the documentation for each class and method for more details.

The current Gradle version can be used from Tooling API versions 1.2 or later. Support for execution using tooling API versions 1.2 to 1.12 is deprecated and will be removed in Gradle 3.0.

The Tooling API requires Java 6 or later. Support for Java 6 is currently deprecated and will be removed in Gradle 3.0.

Part III. Writing Gradle build scripts

Chapter 14. Build Script Basics

14.1. Projects and tasks

Everything in Gradle sits on top of two basic concepts: projects and tasks.

Every Gradle build is made up of one or more projects. What a project represents depends on what it is that you are doing with Gradle. For example, a project might represent a library JAR or a web application. It might represent a distribution ZIP assembled from the JARs produced by other projects. A project does not necessarily represent a thing to be built. It might represent a thing to be done, such as deploying your application to staging or production environments. Don't worry if this seems a little vague for now. Gradle's build-by-convention support adds a more concrete definition for what a project is.

Each project is made up of one or more tasks. A task represents some atomic piece of work which a build performs. This might be compiling some classes, creating a JAR, generating Javadoc, or publishing some archives to a repository.

For now, we will look at defining some simple tasks in a build with one project. Later chapters will look at working with multiple projects and more about working with projects and tasks.

14.2. Hello world

You run a Gradle build using the gradle command. The gradle command looks for a file called build.gradle in the current directory. [5] We call this build.gradle file a build script, although strictly speaking it is a build configuration script, as we will see later. The build script defines a project and its tasks.

To try this out, create the following build script named build.gradle.

Example 14.1. Your first build script

build.gradle

task hello {
    doLast {
        println 'Hello world!'
    }
}

In a command-line shell, move to the containing directory and execute the build script with gradle -q hello:

What does -q do?

Most of the examples in this user guide are run with the -q command-line option. This suppresses Gradle's log messages, so that only the output of the tasks is shown. This keeps the example output in this user guide a little clearer. You don't need to use this option if you don't want to. See Chapter 22, Logging for more details about the command-line options which affect Gradle's output.

Example 14.2. Execution of a build script

Output of gradle -q hello

> gradle -q hello
Hello world!

What's going on here? This build script defines a single task, called hello, and adds an action to it. When you run gradle hello, Gradle executes the hello task, which in turn executes the action you've provided. The action is simply a closure containing some Groovy code to execute.

If you think this looks similar to Ant's targets, you would be right. Gradle tasks are the equivalent to Ant targets, but as you will see, they are much more powerful. We have used a different terminology than Ant as we think the word task is more expressive than the word target. Unfortunately this introduces a terminology clash with Ant, as Ant calls its commands, such as javac or copy, tasks. So when we talk about tasks, we always mean Gradle tasks, which are the equivalent to Ant's targets. If we talk about Ant tasks (Ant commands), we explicitly say Ant task.

14.3. A shortcut task definition

There is a shorthand way to define a task like our hello task above, which is more concise.

Example 14.3. A task definition shortcut

build.gradle

task hello << {
    println 'Hello world!'
}

Again, this defines a task called hello with a single closure to execute. We will use this task definition style throughout the user guide.

14.4. Build scripts are code

Gradle's build scripts give you the full power of Groovy. As an appetizer, have a look at this:

Example 14.4. Using Groovy in Gradle's tasks

build.gradle

task upper << {
    String someString = 'mY_nAmE'
    println "Original: " + someString 
    println "Upper case: " + someString.toUpperCase()
}

Output of gradle -q upper

> gradle -q upper
Original: mY_nAmE
Upper case: MY_NAME

or

Example 14.5. Using Groovy in Gradle's tasks

build.gradle

task count << {
    4.times { print "$it " }
}

Output of gradle -q count

> gradle -q count
0 1 2 3 

14.5. Task dependencies

As you probably have guessed, you can declare tasks that depend on other tasks.

Example 14.6. Declaration of task that depends on other task

build.gradle

task hello << {
    println 'Hello world!'
}
task intro(dependsOn: hello) << {
    println "I'm Gradle"
}

Output of gradle -q intro

> gradle -q intro
Hello world!
I'm Gradle

To add a dependency, the corresponding task does not need to exist.

Example 14.7. Lazy dependsOn - the other task does not exist (yet)

build.gradle

task taskX(dependsOn: 'taskY') << {
    println 'taskX'
}
task taskY << {
    println 'taskY'
}

Output of gradle -q taskX

> gradle -q taskX
taskY
taskX

The dependency of taskX to taskY is declared before taskY is defined. This is very important for multi-project builds. Task dependencies are discussed in more detail in Section 17.4, “Adding dependencies to a task”.

Please notice that you can't use shortcut notation (see Section 14.8, “Shortcut notations”) when referring to a task that is not yet defined.

14.6. Dynamic tasks

The power of Groovy can be used for more than defining what a task does. For example, you can also use it to dynamically create tasks.

Example 14.8. Dynamic creation of a task

build.gradle

4.times { counter ->
    task "task$counter" << {
        println "I'm task number $counter"
    }
}

Output of gradle -q task1

> gradle -q task1
I'm task number 1

14.7. Manipulating existing tasks

Once tasks are created they can be accessed via an API. For instance, you could use this to dynamically add dependencies to a task, at runtime. Ant doesn't allow anything like this.

Example 14.9. Accessing a task via API - adding a dependency

build.gradle

4.times { counter ->
    task "task$counter" << {
        println "I'm task number $counter"
    }
}
task0.dependsOn task2, task3

Output of gradle -q task0

> gradle -q task0
I'm task number 2
I'm task number 3
I'm task number 0

Or you can add behavior to an existing task.

Example 14.10. Accessing a task via API - adding behaviour

build.gradle

task hello << {
    println 'Hello Earth'
}
hello.doFirst {
    println 'Hello Venus'
}
hello.doLast {
    println 'Hello Mars'
}
hello << {
    println 'Hello Jupiter'
}

Output of gradle -q hello

> gradle -q hello
Hello Venus
Hello Earth
Hello Mars
Hello Jupiter

The calls doFirst and doLast can be executed multiple times. They add an action to the beginning or the end of the task's actions list. When the task executes, the actions in the action list are executed in order. The << operator is simply an alias for doLast.

14.8. Shortcut notations

As you might have noticed in the previous examples, there is a convenient notation for accessing an existing task. Each task is available as a property of the build script:

Example 14.11. Accessing task as a property of the build script

build.gradle

task hello << {
    println 'Hello world!'
}
hello.doLast {
    println "Greetings from the $hello.name task."
}

Output of gradle -q hello

> gradle -q hello
Hello world!
Greetings from the hello task.

This enables very readable code, especially when using the tasks provided by the plugins, like the compile task.

14.9. Extra task properties

You can add your own properties to a task. To add a property named myProperty, set ext.myProperty to an initial value. From that point on, the property can be read and set like a predefined task property.

Example 14.12. Adding extra properties to a task

build.gradle

task myTask {
    ext.myProperty = "myValue"
}

task printTaskProperties << {
    println myTask.myProperty
}

Output of gradle -q printTaskProperties

> gradle -q printTaskProperties
myValue

Extra properties aren't limited to tasks. You can read more about them in Section 16.4.2, “Extra properties”.

14.10. Using Ant Tasks

Ant tasks are first-class citizens in Gradle. Gradle provides excellent integration for Ant tasks by simply relying on Groovy. Groovy is shipped with the fantastic AntBuilder. Using Ant tasks from Gradle is as convenient and more powerful than using Ant tasks from a build.xml file. From the example below, you can learn how to execute Ant tasks and how to access Ant properties:

Example 14.13. Using AntBuilder to execute ant.loadfile target

build.gradle

task loadfile << {
    def files = file('../antLoadfileResources').listFiles().sort()
    files.each { File file ->
        if (file.isFile()) {
            ant.loadfile(srcFile: file, property: file.name)
            println " *** $file.name ***"
            println "${ant.properties[file.name]}"
        }
    }
}

Output of gradle -q loadfile

> gradle -q loadfile
 *** agile.manifesto.txt ***
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration  over contract negotiation
Responding to change over following a plan
 *** gradle.manifesto.txt ***
Make the impossible possible, make the possible easy and make the easy elegant.
(inspired by Moshe Feldenkrais)

There is lots more you can do with Ant in your build scripts. You can find out more in Chapter 19, Using Ant from Gradle.

14.11. Using methods

Gradle scales in how you can organize your build logic. The first level of organizing your build logic for the example above, is extracting a method.

Example 14.14. Using methods to organize your build logic

build.gradle

task checksum << {
    fileList('../antLoadfileResources').each {File file ->
        ant.checksum(file: file, property: "cs_$file.name")
        println "$file.name Checksum: ${ant.properties["cs_$file.name"]}"
    }
}

task loadfile << {
    fileList('../antLoadfileResources').each {File file ->
        ant.loadfile(srcFile: file, property: file.name)
        println "I'm fond of $file.name"
    }
}

File[] fileList(String dir) {
    file(dir).listFiles({file -> file.isFile() } as FileFilter).sort()
}

Output of gradle -q loadfile

> gradle -q loadfile
I'm fond of agile.manifesto.txt
I'm fond of gradle.manifesto.txt

Later you will see that such methods can be shared among subprojects in multi-project builds. If your build logic becomes more complex, Gradle offers you other very convenient ways to organize it. We have devoted a whole chapter to this. See Chapter 41, Organizing Build Logic.

14.12. Default tasks

Gradle allows you to define one or more default tasks that are executed if no other tasks are specified.

Example 14.15. Defining a default task

build.gradle

defaultTasks 'clean', 'run'

task clean << {
    println 'Default Cleaning!'
}

task run << {
    println 'Default Running!'
}

task other << {
    println "I'm not a default task!"
}

Output of gradle -q

> gradle -q
Default Cleaning!
Default Running!

This is equivalent to running gradle clean run. In a multi-project build every subproject can have its own specific default tasks. If a subproject does not specify default tasks, the default tasks of the parent project are used (if defined).

14.13. Configure by DAG

As we later describe in full detail (see Chapter 20, The Build Lifecycle), Gradle has a configuration phase and an execution phase. After the configuration phase, Gradle knows all tasks that should be executed. Gradle offers you a hook to make use of this information. A use-case for this would be to check if the release task is among the tasks to be executed. Depending on this, you can assign different values to some variables.

In the following example, execution of the distribution and release tasks results in different value of the version variable.

Example 14.16. Different outcomes of build depending on chosen tasks

build.gradle

task distribution << {
    println "We build the zip with version=$version"
}

task release(dependsOn: 'distribution') << {
    println 'We release now'
}

gradle.taskGraph.whenReady {taskGraph ->
    if (taskGraph.hasTask(release)) {
        version = '1.0'
    } else {
        version = '1.0-SNAPSHOT'
    }
}

Output of gradle -q distribution

> gradle -q distribution
We build the zip with version=1.0-SNAPSHOT

Output of gradle -q release

> gradle -q release
We build the zip with version=1.0
We release now

The important thing is that whenReady affects the release task before the release task is executed. This works even when the release task is not the primary task (i.e., the task passed to the gradle command).

14.14. Where to next?

In this chapter, we have had a first look at tasks. But this is not the end of the story for tasks. If you want to jump into more of the details, have a look at Chapter 17, More about Tasks.

Otherwise, continue on to the tutorials in Chapter 44, Java Quickstart and Chapter 7, Dependency Management Basics.



[5] There are command line switches to change this behavior. See Appendix D, Gradle Command Line)

Chapter 15. Build Init Plugin

The Build Init plugin is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The Gradle Build Init plugin can be used to bootstrap the process of creating a new Gradle build. It supports creating brand new projects of different types as well as converting existing builds (e.g. An Apache Maven build) to be Gradle builds.

Gradle plugins typically need to be applied to a project before they can be used (see Section 25.3, “Applying plugins”). The Build Init plugin is an automatically applied plugin, which means you do not need to apply it explicitly. To use the plugin, simply execute the task named init where you would like to create the Gradle build. There is no need to create a “stub” build.gradle file in order to apply the plugin.

It also leverages the wrapper task from the Wrapper plugin (see Chapter 21, Wrapper Plugin), which means that the Gradle Wrapper will also be installed into the project.

15.1. Tasks

The plugin adds the following tasks to the project:

Table 15.1. Build Init plugin - tasks

Task name Depends on Type Description
init wrapper InitBuild Generates a Gradle project.
wrapper - Wrapper Generates Gradle wrapper files.

15.2. What to set up

The init supports different build setup types. The type is specified by supplying a --type argument value. For example, to create a Java library project simply execute: gradle init --type java-library.

If a --type parameter is not supplied, Gradle will attempt to infer the type from the environment. For example, it will infer a type value of “pom” if it finds a pom.xml to convert to a Gradle build.

If the type could not be inferred, the type “basic” will be used.

All build setup types include the setup of the Gradle Wrapper.

15.3. Build init types

As this plugin is currently incubating, only a few build init types are currently supported. More types will be added in future Gradle releases.

15.3.1. “pom” (Maven conversion)

The “pom” type can be used to convert an Apache Maven build to a Gradle build. This works by converting the POM to one or more Gradle files. It is only able to be used if there is a valid “pom.xml” file in the directory that the init task is invoked in or, if invoked via the "-p" commandline option, in the specified project directory. This “pom” type will be automatically inferred if such a file exists.

The Maven conversion implementation was inspired by the maven2gradle tool that was originally developed by Gradle community members.

The conversion process has the following features:

  • Uses effective POM and effective settings (support for POM inheritance, dependency management, properties)
  • Supports both single module and multimodule projects
  • Supports custom module names (that differ from directory names)
  • Generates general metadata - id, description and version
  • Applies maven, java and war plugins (as needed)
  • Supports packaging war projects as jars if needed
  • Generates dependencies (both external and inter-module)
  • Generates download repositories (inc. local Maven repository)
  • Adjusts Java compiler settings
  • Supports packaging of sources and tests
  • Supports TestNG runner
  • Generates global exclusions from Maven enforcer plugin settings

15.3.2. “java-library

The “java-library” build init type is not inferable. It must be explicitly specified.

It has the following features:

  • Uses the “java” plugin
  • Uses the “jcenter” dependency repository
  • Uses JUnit for testing
  • Has directories in the conventional locations for source code
  • Contains a sample class and unit test, if there are no existing source or test files

Alternative test framework can be specified by supplying a --test-framework argument value. To use a different test framework, execute one of the following commands:

  • gradle init --type java-library --test-framework spock: Uses Spock for testing instead of JUnit
  • gradle init --type java-library --test-framework testng: Uses TestNG for testing instead of JUnit

15.3.3. “scala-library

The “scala-library” build init type is not inferable. It must be explicitly specified.

It has the following features:

  • Uses the “scala” plugin
  • Uses the “jcenter” dependency repository
  • Uses Scala 2.10
  • Uses ScalaTest for testing
  • Has directories in the conventional locations for source code
  • Contains a sample scala class and an associated ScalaTest test suite, if there are no existing source or test files
  • Uses the Zinc Scala compiler by default

15.3.4. “groovy-library

The “groovy-library” build init type is not inferable. It must be explicitly specified.

It has the following features:

  • Uses the “groovy” plugin
  • Uses the “jcenter” dependency repository
  • Uses Groovy 2.x
  • Uses Spock testing framework for testing
  • Has directories in the conventional locations for source code
  • Contains a sample Groovy class and an associated Spock specification, if there are no existing source or test files

15.3.5. “basic”

The “basic” build init type is useful for creating a fresh new Gradle project. It creates a sample build.gradle file, with comments and links to help get started.

This type is used when no type was explicitly specified, and no type could be inferred.

Chapter 16. Writing Build Scripts

This chapter looks at some of the details of writing a build script.

16.1. The Gradle build language

Gradle provides a domain specific language, or DSL, for describing builds. This build language is based on Groovy, with some additions to make it easier to describe a build.

A build script can contain any Groovy language element. [6] Gradle assumes that each build script is encoded using UTF-8.

16.2. The Project API

In the tutorial in Chapter 44, Java Quickstart we used, for example, the apply() method. Where does this method come from? We said earlier that the build script defines a project in Gradle. For each project in the build, Gradle creates an object of type Project and associates this Project object with the build script. As the build script executes, it configures this Project object:

Getting help writing build scripts

Don't forget that your build script is simply Groovy code that drives the Gradle API. And the Project interface is your starting point for accessing everything in the Gradle API. So, if you're wondering what 'tags' are available in your build script, you can start with the documentation for the Project interface.

  • Any method you call in your build script which is not defined in the build script, is delegated to the Project object.

  • Any property you access in your build script, which is not defined in the build script, is delegated to the Project object.

Let's try this out and try to access the name property of the Project object.

Example 16.1. Accessing property of the Project object

build.gradle

println name
println project.name

Output of gradle -q check

> gradle -q check
projectApi
projectApi

Both println statements print out the same property. The first uses auto-delegation to the Project object, for properties not defined in the build script. The other statement uses the project property available to any build script, which returns the associated Project object. Only if you define a property or a method which has the same name as a member of the Project object, would you need to use the project property.

16.2.1. Standard project properties

The Project object provides some standard properties, which are available in your build script. The following table lists a few of the commonly used ones.

Table 16.1. Project Properties

Name Type Default Value
project Project The Project instance
name String The name of the project directory.
path String The absolute path of the project.
description String A description for the project.
projectDir File The directory containing the build script.
buildDir File projectDir/build
group Object unspecified
version Object unspecified
ant AntBuilder An AntBuilder instance

16.3. The Script API

When Gradle executes a script, it compiles the script into a class which implements Script. This means that all of the properties and methods declared by the Script interface are available in your script.

16.4. Declaring variables

There are two kinds of variables that can be declared in a build script: local variables and extra properties.

16.4.1. Local variables

Local variables are declared with the def keyword. They are only visible in the scope where they have been declared. Local variables are a feature of the underlying Groovy language.

Example 16.2. Using local variables

build.gradle

def dest = "dest"

task copy(type: Copy) {
    from "source"
    into dest
}

16.4.2. Extra properties

All enhanced objects in Gradle's domain model can hold extra user-defined properties. This includes, but is not limited to, projects, tasks, and source sets. Extra properties can be added, read and set via the owning object's ext property. Alternatively, an ext block can be used to add multiple properties at once.

Example 16.3. Using extra properties

build.gradle

apply plugin: "java"

ext {
    springVersion = "3.1.0.RELEASE"
    emailNotification = "build@master.org"
}

sourceSets.all { ext.purpose = null }

sourceSets {
    main {
        purpose = "production"
    }
    test {
        purpose = "test"
    }
    plugin {
        purpose = "production"
    }
}

task printProperties << {
    println springVersion
    println emailNotification
    sourceSets.matching { it.purpose == "production" }.each { println it.name }
}

Output of gradle -q printProperties

> gradle -q printProperties
3.1.0.RELEASE
build@master.org
main
plugin

In this example, an ext block adds two extra properties to the project object. Additionally, a property named purpose is added to each source set by setting ext.purpose to null (null is a permissible value). Once the properties have been added, they can be read and set like predefined properties.

By requiring special syntax for adding a property, Gradle can fail fast when an attempt is made to set a (predefined or extra) property but the property is misspelled or does not exist. Extra properties can be accessed from anywhere their owning object can be accessed, giving them a wider scope than local variables. Extra properties on a project are visible from its subprojects.

For further details on extra properties and their API, see the ExtraPropertiesExtension class in the API documentation.

16.5. Configuring arbitrary objects

You can configure arbitrary objects in the following very readable way.

Example 16.4. Configuring arbitrary objects

build.gradle

task configure << {
    def pos = configure(new java.text.FieldPosition(10)) {
        beginIndex = 1
        endIndex = 5
    }
    println pos.beginIndex
    println pos.endIndex
}

Output of gradle -q configure

> gradle -q configure
1
5

16.6. Configuring arbitrary objects using an external script

You can also configure arbitrary objects using an external script.

Example 16.5. Configuring arbitrary objects using a script

build.gradle

task configure << {
    def pos = new java.text.FieldPosition(10)
    // Apply the script
    apply from: 'other.gradle', to: pos
    println pos.beginIndex
    println pos.endIndex
}

other.gradle

// Set properties.
beginIndex = 1
endIndex = 5

Output of gradle -q configure

> gradle -q configure
1
5

16.7. Some Groovy basics

The Groovy language provides plenty of features for creating DSLs, and the Gradle build language takes advantage of these. Understanding how the build language works will help you when you write your build script, and in particular, when you start to write custom plugins and tasks.

16.7.1. Groovy JDK

Groovy adds lots of useful methods to the standard Java classes. For example, Iterable gets an each method, which iterates over the elements of the Iterable:

Example 16.6. Groovy JDK methods

build.gradle

// Iterable gets an each() method
configurations.runtime.each { File f -> println f }

Have a look at http://groovy-lang.org/gdk.html for more details.

16.7.2. Property accessors

Groovy automatically converts a property reference into a call to the appropriate getter or setter method.

Example 16.7. Property accessors

build.gradle

// Using a getter method
println project.buildDir
println getProject().getBuildDir()

// Using a setter method
project.buildDir = 'target'
getProject().setBuildDir('target')

16.7.3. Optional parentheses on method calls

Parentheses are optional for method calls.

Example 16.8. Method call without parentheses

build.gradle

test.systemProperty 'some.prop', 'value'
test.systemProperty('some.prop', 'value')

16.7.4. List and map literals

Groovy provides some shortcuts for defining List and Map instances. Both kinds of literals are straightforward, but map literals have some interesting twists.

For instance, the “apply” method (where you typically apply plugins) actually takes a map parameter. However, when you have a line like “apply plugin:'java'”, you aren't actually using a map literal, you're actually using “named parameters”, which have almost exactly the same syntax as a map literal (without the wrapping brackets). That named parameter list gets converted to a map when the method is called, but it doesn't start out as a map.

Example 16.9. List and map literals

build.gradle

// List literal
test.includes = ['org/gradle/api/**', 'org/gradle/internal/**']

List<String> list = new ArrayList<String>()
list.add('org/gradle/api/**')
list.add('org/gradle/internal/**')
test.includes = list

// Map literal.
Map<String, String> map = [key1:'value1', key2: 'value2']

// Groovy will coerce named arguments
// into a single map argument
apply plugin: 'java'

16.7.5. Closures as the last parameter in a method

The Gradle DSL uses closures in many places. You can find out more about closures here. When the last parameter of a method is a closure, you can place the closure after the method call:

Example 16.10. Closure as method parameter

build.gradle

repositories {
    println "in a closure"
}
repositories() { println "in a closure" }
repositories({ println "in a closure" })

16.7.6. Closure delegate

Each closure has a delegate object, which Groovy uses to look up variable and method references which are not local variables or parameters of the closure. Gradle uses this for configuration closures, where the delegate object is set to the object to be configured.

Example 16.11. Closure delegates

build.gradle

dependencies {
    assert delegate == project.dependencies
    testCompile('junit:junit:4.12')
    delegate.testCompile('junit:junit:4.12')
}

16.8. Default imports

To make build scripts more concise, Gradle automatically adds a set of import statements to the Gradle scripts. This means that instead of using throw new org.gradle.api.tasks.StopExecutionException() you can just type throw new StopExecutionException() instead.

Listed below are the imports added to each script:

Figure 16.1. gradle-imports

import org.gradle.*
import org.gradle.api.*
import org.gradle.api.artifacts.*
import org.gradle.api.artifacts.cache.*
import org.gradle.api.artifacts.component.*
import org.gradle.api.artifacts.dsl.*
import org.gradle.api.artifacts.ivy.*
import org.gradle.api.artifacts.maven.*
import org.gradle.api.artifacts.query.*
import org.gradle.api.artifacts.repositories.*
import org.gradle.api.artifacts.result.*
import org.gradle.api.component.*
import org.gradle.api.credentials.*
import org.gradle.api.distribution.*
import org.gradle.api.distribution.plugins.*
import org.gradle.api.dsl.*
import org.gradle.api.execution.*
import org.gradle.api.file.*
import org.gradle.api.initialization.*
import org.gradle.api.initialization.dsl.*
import org.gradle.api.invocation.*
import org.gradle.api.java.archives.*
import org.gradle.api.logging.*
import org.gradle.api.logging.configuration.*
import org.gradle.api.plugins.*
import org.gradle.api.plugins.announce.*
import org.gradle.api.plugins.antlr.*
import org.gradle.api.plugins.buildcomparison.gradle.*
import org.gradle.api.plugins.jetty.*
import org.gradle.api.plugins.osgi.*
import org.gradle.api.plugins.quality.*
import org.gradle.api.plugins.scala.*
import org.gradle.api.plugins.sonar.*
import org.gradle.api.plugins.sonar.model.*
import org.gradle.api.publish.*
import org.gradle.api.publish.ivy.*
import org.gradle.api.publish.ivy.plugins.*
import org.gradle.api.publish.ivy.tasks.*
import org.gradle.api.publish.maven.*
import org.gradle.api.publish.maven.plugins.*
import org.gradle.api.publish.maven.tasks.*
import org.gradle.api.publish.plugins.*
import org.gradle.api.reporting.*
import org.gradle.api.reporting.components.*
import org.gradle.api.reporting.dependencies.*
import org.gradle.api.reporting.model.*
import org.gradle.api.reporting.plugins.*
import org.gradle.api.resources.*
import org.gradle.api.specs.*
import org.gradle.api.tasks.*
import org.gradle.api.tasks.ant.*
import org.gradle.api.tasks.application.*
import org.gradle.api.tasks.bundling.*
import org.gradle.api.tasks.compile.*
import org.gradle.api.tasks.diagnostics.*
import org.gradle.api.tasks.incremental.*
import org.gradle.api.tasks.javadoc.*
import org.gradle.api.tasks.scala.*
import org.gradle.api.tasks.testing.*
import org.gradle.api.tasks.testing.junit.*
import org.gradle.api.tasks.testing.testng.*
import org.gradle.api.tasks.util.*
import org.gradle.api.tasks.wrapper.*
import org.gradle.authentication.*
import org.gradle.authentication.http.*
import org.gradle.buildinit.plugins.*
import org.gradle.buildinit.tasks.*
import org.gradle.external.javadoc.*
import org.gradle.ide.cdt.*
import org.gradle.ide.cdt.tasks.*
import org.gradle.ide.visualstudio.*
import org.gradle.ide.visualstudio.plugins.*
import org.gradle.ide.visualstudio.tasks.*
import org.gradle.ivy.*
import org.gradle.jvm.*
import org.gradle.jvm.application.scripts.*
import org.gradle.jvm.application.tasks.*
import org.gradle.jvm.platform.*
import org.gradle.jvm.plugins.*
import org.gradle.jvm.tasks.*
import org.gradle.jvm.tasks.api.*
import org.gradle.jvm.test.*
import org.gradle.jvm.toolchain.*
import org.gradle.language.assembler.*
import org.gradle.language.assembler.plugins.*
import org.gradle.language.assembler.tasks.*
import org.gradle.language.base.*
import org.gradle.language.base.artifact.*
import org.gradle.language.base.plugins.*
import org.gradle.language.base.sources.*
import org.gradle.language.c.*
import org.gradle.language.c.plugins.*
import org.gradle.language.c.tasks.*
import org.gradle.language.coffeescript.*
import org.gradle.language.cpp.*
import org.gradle.language.cpp.plugins.*
import org.gradle.language.cpp.tasks.*
import org.gradle.language.java.*
import org.gradle.language.java.artifact.*
import org.gradle.language.java.plugins.*
import org.gradle.language.java.tasks.*
import org.gradle.language.javascript.*
import org.gradle.language.jvm.*
import org.gradle.language.jvm.plugins.*
import org.gradle.language.jvm.tasks.*
import org.gradle.language.nativeplatform.*
import org.gradle.language.nativeplatform.tasks.*
import org.gradle.language.objectivec.*
import org.gradle.language.objectivec.plugins.*
import org.gradle.language.objectivec.tasks.*
import org.gradle.language.objectivecpp.*
import org.gradle.language.objectivecpp.plugins.*
import org.gradle.language.objectivecpp.tasks.*
import org.gradle.language.rc.*
import org.gradle.language.rc.plugins.*
import org.gradle.language.rc.tasks.*
import org.gradle.language.routes.*
import org.gradle.language.scala.*
import org.gradle.language.scala.plugins.*
import org.gradle.language.scala.tasks.*
import org.gradle.language.scala.toolchain.*
import org.gradle.language.twirl.*
import org.gradle.maven.*
import org.gradle.model.*
import org.gradle.nativeplatform.*
import org.gradle.nativeplatform.platform.*
import org.gradle.nativeplatform.plugins.*
import org.gradle.nativeplatform.tasks.*
import org.gradle.nativeplatform.test.*
import org.gradle.nativeplatform.test.cunit.*
import org.gradle.nativeplatform.test.cunit.plugins.*
import org.gradle.nativeplatform.test.cunit.tasks.*
import org.gradle.nativeplatform.test.googletest.*
import org.gradle.nativeplatform.test.googletest.plugins.*
import org.gradle.nativeplatform.test.plugins.*
import org.gradle.nativeplatform.test.tasks.*
import org.gradle.nativeplatform.toolchain.*
import org.gradle.nativeplatform.toolchain.plugins.*
import org.gradle.platform.base.*
import org.gradle.platform.base.binary.*
import org.gradle.platform.base.component.*
import org.gradle.platform.base.plugins.*
import org.gradle.play.*
import org.gradle.play.distribution.*
import org.gradle.play.platform.*
import org.gradle.play.plugins.*
import org.gradle.play.plugins.ide.*
import org.gradle.play.tasks.*
import org.gradle.play.toolchain.*
import org.gradle.plugin.devel.*
import org.gradle.plugin.repository.*
import org.gradle.plugin.use.*
import org.gradle.plugins.ear.*
import org.gradle.plugins.ear.descriptor.*
import org.gradle.plugins.ide.api.*
import org.gradle.plugins.ide.eclipse.*
import org.gradle.plugins.ide.idea.*
import org.gradle.plugins.javascript.base.*
import org.gradle.plugins.javascript.coffeescript.*
import org.gradle.plugins.javascript.envjs.*
import org.gradle.plugins.javascript.envjs.browser.*
import org.gradle.plugins.javascript.envjs.http.*
import org.gradle.plugins.javascript.envjs.http.simple.*
import org.gradle.plugins.javascript.jshint.*
import org.gradle.plugins.javascript.rhino.*
import org.gradle.plugins.javascript.rhino.worker.*
import org.gradle.plugins.signing.*
import org.gradle.plugins.signing.signatory.*
import org.gradle.plugins.signing.signatory.pgp.*
import org.gradle.plugins.signing.type.*
import org.gradle.plugins.signing.type.pgp.*
import org.gradle.process.*
import org.gradle.sonar.runner.*
import org.gradle.sonar.runner.plugins.*
import org.gradle.sonar.runner.tasks.*
import org.gradle.testing.base.*
import org.gradle.testing.base.plugins.*
import org.gradle.testing.jacoco.plugins.*
import org.gradle.testing.jacoco.tasks.*
import org.gradle.testkit.runner.*
import org.gradle.util.*



[6] Any language element except for statement labels.

Chapter 17. More about Tasks

In the introductory tutorial (Chapter 14, Build Script Basics) you learned how to create simple tasks. You also learned how to add additional behavior to these tasks later on, and you learned how to create dependencies between tasks. This was all about simple tasks, but Gradle takes the concept of tasks further. Gradle supports enhanced tasks, which are tasks that have their own properties and methods. This is really different from what you are used to with Ant targets. Such enhanced tasks are either provided by you or built into Gradle.

17.1. Defining tasks

We have already seen how to define tasks using a keyword style in Chapter 14, Build Script Basics. There are a few variations on this style, which you may need to use in certain situations. For example, the keyword style does not work in expressions.

Example 17.1. Defining tasks

build.gradle

task(hello) << {
    println "hello"
}

task(copy, type: Copy) {
    from(file('srcDir'))
    into(buildDir)
}

You can also use strings for the task names:

Example 17.2. Defining tasks - using strings for task names

build.gradle

task('hello') <<
{
    println "hello"
}

task('copy', type: Copy) {
    from(file('srcDir'))
    into(buildDir)
}

There is an alternative syntax for defining tasks, which you may prefer to use:

Example 17.3. Defining tasks with alternative syntax

build.gradle

tasks.create(name: 'hello') << {
    println "hello"
}

tasks.create(name: 'copy', type: Copy) {
    from(file('srcDir'))
    into(buildDir)
}

Here we add tasks to the tasks collection. Have a look at TaskContainer for more variations of the create() method.

17.2. Locating tasks

You often need to locate the tasks that you have defined in the build file, for example, to configure them or use them for dependencies. There are a number of ways of doing this. Firstly, each task is available as a property of the project, using the task name as the property name:

Example 17.4. Accessing tasks as properties

build.gradle

task hello

println hello.name
println project.hello.name

Tasks are also available through the tasks collection.

Example 17.5. Accessing tasks via tasks collection

build.gradle

task hello

println tasks.hello.name
println tasks['hello'].name

You can access tasks from any project using the task's path using the tasks.getByPath() method. You can call the getByPath() method with a task name, or a relative path, or an absolute path.

Example 17.6. Accessing tasks by path

build.gradle

project(':projectA') {
    task hello
}

task hello

println tasks.getByPath('hello').path
println tasks.getByPath(':hello').path
println tasks.getByPath('projectA:hello').path
println tasks.getByPath(':projectA:hello').path

Output of gradle -q hello

> gradle -q hello
:hello
:hello
:projectA:hello
:projectA:hello

Have a look at TaskContainer for more options for locating tasks.

17.3. Configuring tasks

As an example, let's look at the Copy task provided by Gradle. To create a Copy task for your build, you can declare in your build script:

Example 17.7. Creating a copy task

build.gradle

task myCopy(type: Copy)

This creates a copy task with no default behavior. The task can be configured using its API (see Copy). The following examples show several different ways to achieve the same configuration.

Just to be clear, realize that the name of this task is “myCopy”, but it is of typeCopy”. You can have multiple tasks of the same type, but with different names. You'll find this gives you a lot of power to implement cross-cutting concerns across all tasks of a particular type.

Example 17.8. Configuring a task - various ways

build.gradle

Copy myCopy = task(myCopy, type: Copy)
myCopy.from 'resources'
myCopy.into 'target'
myCopy.include('**/*.txt', '**/*.xml', '**/*.properties')

This is similar to the way we would configure objects in Java. You have to repeat the context (myCopy) in the configuration statement every time. This is a redundancy and not very nice to read.

There is another way of configuring a task. It also preserves the context and it is arguably the most readable. It is usually our favorite.

Example 17.9. Configuring a task - with closure

build.gradle

task myCopy(type: Copy)

myCopy {
   from 'resources'
   into 'target'
   include('**/*.txt', '**/*.xml', '**/*.properties')
}

This works for any task. Line 3 of the example is just a shortcut for the tasks.getByName() method. It is important to note that if you pass a closure to the getByName() method, this closure is applied to configure the task, not when the task executes.

You can also use a configuration closure when you define a task.

Example 17.10. Defining a task with closure

build.gradle

task copy(type: Copy) {
   from 'resources'
   into 'target'
   include('**/*.txt', '**/*.xml', '**/*.properties')
}

Don't forget about the build phases

A task has both configuration and actions. When using the <<, you are simply using a shortcut to define an action. Code defined in the configuration section of your task will get executed during the configuration phase of the build regardless of what task was targeted. See Chapter 20, The Build Lifecycle for more details about the build lifecycle.

17.4. Adding dependencies to a task

There are several ways you can define the dependencies of a task. In Section 14.5, “Task dependencies” you were introduced to defining dependencies using task names. Task names can refer to tasks in the same project as the task, or to tasks in other projects. To refer to a task in another project, you prefix the name of the task with the path of the project it belongs to. The following is an example which adds a dependency from projectA:taskX to projectB:taskY:

Example 17.11. Adding dependency on task from another project

build.gradle

project('projectA') {
    task taskX(dependsOn: ':projectB:taskY') << {
        println 'taskX'
    }
}

project('projectB') {
    task taskY << {
        println 'taskY'
    }
}

Output of gradle -q taskX

> gradle -q taskX
taskY
taskX

Instead of using a task name, you can define a dependency using a Task object, as shown in this example:

Example 17.12. Adding dependency using task object

build.gradle

task taskX << {
    println 'taskX'
}

task taskY << {
    println 'taskY'
}

taskX.dependsOn taskY

Output of gradle -q taskX

> gradle -q taskX
taskY
taskX

For more advanced uses, you can define a task dependency using a closure. When evaluated, the closure is passed the task whose dependencies are being calculated. The closure should return a single Task or collection of Task objects, which are then treated as dependencies of the task. The following example adds a dependency from taskX to all the tasks in the project whose name starts with lib:

Example 17.13. Adding dependency using closure

build.gradle

task taskX << {
    println 'taskX'
}

taskX.dependsOn {
    tasks.findAll { task -> task.name.startsWith('lib') }
}

task lib1 << {
    println 'lib1'
}

task lib2 << {
    println 'lib2'
}

task notALib << {
    println 'notALib'
}

Output of gradle -q taskX

> gradle -q taskX
lib1
lib2
taskX

For more information about task dependencies, see the Task API.

17.5. Ordering tasks

Task ordering is an incubating feature. Please be aware that this feature may change in later Gradle versions.

In some cases it is useful to control the order in which 2 tasks will execute, without introducing an explicit dependency between those tasks. The primary difference between a task ordering and a task dependency is that an ordering rule does not influence which tasks will be executed, only the order in which they will be executed.

Task ordering can be useful in a number of scenarios:

  • Enforce sequential ordering of tasks: eg. 'build' never runs before 'clean'.
  • Run build validations early in the build: eg. validate I have the correct credentials before starting the work for a release build.
  • Get feedback faster by running quick verification tasks before long verification tasks: eg. unit tests should run before integration tests.
  • A task that aggregates the results of all tasks of a particular type: eg. test report task combines the outputs of all executed test tasks.

There are two ordering rules available: “must run after” and “should run after”.

When you use the “must run after” ordering rule you specify that taskB must always run after taskA, whenever both taskA and taskB will be run. This is expressed as taskB.mustRunAfter(taskA). The “should run after” ordering rule is similar but less strict as it will be ignored in two situations. Firstly if using that rule introduces an ordering cycle. Secondly when using parallel execution and all dependencies of a task have been satisfied apart from the “should run after” task, then this task will be run regardless of whether its “should run after” dependencies have been run or not. You should use “should run after” where the ordering is helpful but not strictly required.

With these rules present it is still possible to execute taskA without taskB and vice-versa.

Example 17.14. Adding a 'must run after' task ordering

build.gradle

task taskX << {
    println 'taskX'
}
task taskY << {
    println 'taskY'
}
taskY.mustRunAfter taskX

Output of gradle -q taskY taskX

> gradle -q taskY taskX
taskX
taskY

Example 17.15. Adding a 'should run after' task ordering

build.gradle

task taskX << {
    println 'taskX'
}
task taskY << {
    println 'taskY'
}
taskY.shouldRunAfter taskX

Output of gradle -q taskY taskX

> gradle -q taskY taskX
taskX
taskY

In the examples above, it is still possible to execute taskY without causing taskX to run:

Example 17.16. Task ordering does not imply task execution

Output of gradle -q taskY

> gradle -q taskY
taskY

To specify a “must run after” or “should run after” ordering between 2 tasks, you use the Task.mustRunAfter(java.lang.Object[]) and Task.shouldRunAfter(java.lang.Object[]) methods. These methods accept a task instance, a task name or any other input accepted by Task.dependsOn(java.lang.Object[]).

Note that “B.mustRunAfter(A)” or “B.shouldRunAfter(A)” does not imply any execution dependency between the tasks:

  • It is possible to execute tasks A and B independently. The ordering rule only has an effect when both tasks are scheduled for execution.
  • When run with --continue, it is possible for B to execute in the event that A fails.

As mentioned before, the “should run after” ordering rule will be ignored if it introduces an ordering cycle:

Example 17.17. A 'should run after' task ordering is ignored if it introduces an ordering cycle

build.gradle

task taskX << {
    println 'taskX'
}
task taskY << {
    println 'taskY'
}
task taskZ << {
    println 'taskZ'
}
taskX.dependsOn taskY
taskY.dependsOn taskZ
taskZ.shouldRunAfter taskX

Output of gradle -q taskX

> gradle -q taskX
taskZ
taskY
taskX

17.6. Adding a description to a task

You can add a description to your task. This description is displayed when executing gradle tasks.

Example 17.18. Adding a description to a task

build.gradle

task copy(type: Copy) {
   description 'Copies the resource directory to the target directory.'
   from 'resources'
   into 'target'
   include('**/*.txt', '**/*.xml', '**/*.properties')
}

17.7. Replacing tasks

Sometimes you want to replace a task. For example, if you want to exchange a task added by the Java plugin with a custom task of a different type. You can achieve this with:

Example 17.19. Overwriting a task

build.gradle

task copy(type: Copy)

task copy(overwrite: true) << {
    println('I am the new one.')
}

Output of gradle -q copy

> gradle -q copy
I am the new one.

This will replace a task of type Copy with the task you've defined, because it uses the same name. When you define the new task, you have to set the overwrite property to true. Otherwise Gradle throws an exception, saying that a task with that name already exists.

17.8. Skipping tasks

Gradle offers multiple ways to skip the execution of a task.

17.8.1. Using a predicate

You can use the onlyIf() method to attach a predicate to a task. The task's actions are only executed if the predicate evaluates to true. You implement the predicate as a closure. The closure is passed the task as a parameter, and should return true if the task should execute and false if the task should be skipped. The predicate is evaluated just before the task is due to be executed.

Example 17.20. Skipping a task using a predicate

build.gradle

task hello << {
    println 'hello world'
}

hello.onlyIf { !project.hasProperty('skipHello') }

Output of gradle hello -PskipHello

> gradle hello -PskipHello
:hello SKIPPED

BUILD SUCCESSFUL

Total time: 1 secs

17.8.2. Using StopExecutionException

If the logic for skipping a task can't be expressed with a predicate, you can use the StopExecutionException. If this exception is thrown by an action, the further execution of this action as well as the execution of any following action of this task is skipped. The build continues with executing the next task.

Example 17.21. Skipping tasks with StopExecutionException

build.gradle

task compile << {
    println 'We are doing the compile.'
}

compile.doFirst {
    // Here you would put arbitrary conditions in real life.
    // But this is used in an integration test so we want defined behavior.
    if (true) { throw new StopExecutionException() }
}
task myTask(dependsOn: 'compile') << {
   println 'I am not affected'
}

Output of gradle -q myTask

> gradle -q myTask
I am not affected

This feature is helpful if you work with tasks provided by Gradle. It allows you to add conditional execution of the built-in actions of such a task. [7]

17.8.3. Enabling and disabling tasks

Every task has an enabled flag which defaults to true. Setting it to false prevents the execution of any of the task's actions.

Example 17.22. Enabling and disabling tasks

build.gradle

task disableMe << {
    println 'This should not be printed if the task is disabled.'
}
disableMe.enabled = false

Output of gradle disableMe

> gradle disableMe
:disableMe SKIPPED

BUILD SUCCESSFUL

Total time: 1 secs

17.9. Skipping tasks that are up-to-date

If you are using one of the tasks that come with Gradle, such as a task added by the Java plugin, you might have noticed that Gradle will skip tasks that are up-to-date. This behaviour is also available for your tasks, not just for built-in tasks.

17.9.1. Declaring a task's inputs and outputs

Let's have a look at an example. Here our task generates several output files from a source XML file. Let's run it a couple of times.

Example 17.23. A generator task

build.gradle

task transform {
    ext.srcFile = file('mountains.xml')
    ext.destDir = new File(buildDir, 'generated')
    doLast {
        println "Transforming source file."
        destDir.mkdirs()
        def mountains = new XmlParser().parse(srcFile)
        mountains.mountain.each { mountain ->
            def name = mountain.name[0].text()
            def height = mountain.height[0].text()
            def destFile = new File(destDir, "${name}.txt")
            destFile.text = "$name -> ${height}\n"
        }
    }
}

Output of gradle transform

> gradle transform
:transform
Transforming source file.

Output of gradle transform

> gradle transform
:transform
Transforming source file.

Notice that Gradle executes this task a second time, and does not skip the task even though nothing has changed. Our example task was defined using an action closure. Gradle has no idea what the closure does and cannot automatically figure out whether the task is up-to-date or not. To use Gradle's up-to-date checking, you need to declare the inputs and outputs of the task.

Each task has an inputs and outputs property, which you use to declare the inputs and outputs of the task. Below, we have changed our example to declare that it takes the source XML file as an input and produces output to a destination directory. Let's run it a couple of times.

Example 17.24. Declaring the inputs and outputs of a task

build.gradle

task transform {
    ext.srcFile = file('mountains.xml')
    ext.destDir = new File(buildDir, 'generated')
    inputs.file srcFile
    outputs.dir destDir
    doLast {
        println "Transforming source file."
        destDir.mkdirs()
        def mountains = new XmlParser().parse(srcFile)
        mountains.mountain.each { mountain ->
            def name = mountain.name[0].text()
            def height = mountain.height[0].text()
            def destFile = new File(destDir, "${name}.txt")
            destFile.text = "$name -> ${height}\n"
        }
    }
}

Output of gradle transform

> gradle transform
:transform
Transforming source file.

Output of gradle transform

> gradle transform
:transform UP-TO-DATE

Now, Gradle knows which files to check to determine whether the task is up-to-date or not.

The task's inputs property is of type TaskInputs. The task's outputs property is of type TaskOutputs.

A task with no defined outputs will never be considered up-to-date. For scenarios where the outputs of a task are not files, or for more complex scenarios, the TaskOutputs.upToDateWhen(groovy.lang.Closure) method allows you to calculate programmatically if the tasks outputs should be considered up to date.

A task with only outputs defined will be considered up-to-date if those outputs are unchanged since the previous build.

17.9.2. How does it work?

Before a task is executed for the first time, Gradle takes a snapshot of the inputs. This snapshot contains the set of input files and a hash of the contents of each file. Gradle then executes the task. If the task completes successfully, Gradle takes a snapshot of the outputs. This snapshot contains the set of output files and a hash of the contents of each file. Gradle persists both snapshots for the next time the task is executed.

Each time after that, before the task is executed, Gradle takes a new snapshot of the inputs and outputs. If the new snapshots are the same as the previous snapshots, Gradle assumes that the outputs are up to date and skips the task. If they are not the same, Gradle executes the task. Gradle persists both snapshots for the next time the task is executed.

Note that if a task has an output directory specified, any files added to that directory since the last time it was executed are ignored and will NOT cause the task to be out of date. This is so unrelated tasks may share an output directory without interfering with each other. If this is not the behaviour you want for some reason, consider using TaskOutputs.upToDateWhen(groovy.lang.Closure)

17.10. Task rules

Sometimes you want to have a task whose behavior depends on a large or infinite number value range of parameters. A very nice and expressive way to provide such tasks are task rules:

Example 17.25. Task rule

build.gradle

tasks.addRule("Pattern: ping<ID>") { String taskName ->
    if (taskName.startsWith("ping")) {
        task(taskName) << {
            println "Pinging: " + (taskName - 'ping')
        }
    }
}

Output of gradle -q pingServer1

> gradle -q pingServer1
Pinging: Server1

The String parameter is used as a description for the rule, which is shown with gradle tasks.

Rules are not only used when calling tasks from the command line. You can also create dependsOn relations on rule based tasks:

Example 17.26. Dependency on rule based tasks

build.gradle

tasks.addRule("Pattern: ping<ID>") { String taskName ->
    if (taskName.startsWith("ping")) {
        task(taskName) << {
            println "Pinging: " + (taskName - 'ping')
        }
    }
}

task groupPing {
    dependsOn pingServer1, pingServer2
}

Output of gradle -q groupPing

> gradle -q groupPing
Pinging: Server1
Pinging: Server2

If you run “gradle -q tasks” you won't find a task named “pingServer1” or “pingServer2”, but this script is executing logic based on the request to run those tasks.

17.11. Finalizer tasks

Finalizers tasks are an incubating feature (see Section C.1.2, “Incubating”).

Finalizer tasks are automatically added to the task graph when the finalized task is scheduled to run.

Example 17.27. Adding a task finalizer

build.gradle

task taskX << {
    println 'taskX'
}
task taskY << {
    println 'taskY'
}

taskX.finalizedBy taskY

Output of gradle -q taskX

> gradle -q taskX
taskX
taskY

Finalizer tasks will be executed even if the finalized task fails.

Example 17.28. Task finalizer for a failing task

build.gradle

task taskX << {
    println 'taskX'
    throw new RuntimeException()
}
task taskY << {
    println 'taskY'
}

taskX.finalizedBy taskY

Output of gradle -q taskX

> gradle -q taskX
taskX
taskY

On the other hand, finalizer tasks are not executed if the finalized task didn't do any work, for example if it is considered up to date or if a dependent task fails.

Finalizer tasks are useful in situations where the build creates a resource that has to be cleaned up regardless of the build failing or succeeding. An example of such a resource is a web container that is started before an integration test task and which should be always shut down, even if some of the tests fail.

To specify a finalizer task you use the Task.finalizedBy(java.lang.Object[]) method. This method accepts a task instance, a task name, or any other input accepted by Task.dependsOn(java.lang.Object[]).

17.12. Summary

If you are coming from Ant, an enhanced Gradle task like Copy seems like a cross between an Ant target and an Ant task. Although Ant's tasks and targets are really different entities, Gradle combines these notions into a single entity. Simple Gradle tasks are like Ant's targets, but enhanced Gradle tasks also include aspects of Ant tasks. All of Gradle's tasks share a common API and you can create dependencies between them. These tasks are much easier to configure than an Ant task. They make full use of the type system, and are more expressive and easier to maintain.



[7] You might be wondering why there is neither an import for the StopExecutionException nor do we access it via its fully qualified name. The reason is, that Gradle adds a set of default imports to your script (see Section 16.8, “Default imports”).

Chapter 18. Working With Files

Most builds work with files. Gradle adds some concepts and APIs to help you achieve this.

18.1. Locating files

You can locate a file relative to the project directory using the Project.file(java.lang.Object) method.

Example 18.1. Locating files

build.gradle

// Using a relative path
File configFile = file('src/config.xml')

// Using an absolute path
configFile = file(configFile.absolutePath)

// Using a File object with a relative path
configFile = file(new File('src/config.xml'))

You can pass any object to the file() method, and it will attempt to convert the value to an absolute File object. Usually, you would pass it a String or File instance. If this path is an absolute path, it is used to construct a File instance. Otherwise, a File instance is constructed by prepending the project directory path to the supplied path. The file() method also understands URLs, such as file:/some/path.xml.

Using this method is a useful way to convert some user provided value into an absolute File. It is preferable to using new File(somePath), as file() always evaluates the supplied path relative to the project directory, which is fixed, rather than the current working directory, which can change depending on how the user runs Gradle.

18.2. File collections

A file collection is simply a set of files. It is represented by the FileCollection interface. Many objects in the Gradle API implement this interface. For example, dependency configurations implement FileCollection.

One way to obtain a FileCollection instance is to use the Project.files(java.lang.Object[]) method. You can pass this method any number of objects, which are then converted into a set of File objects. The files() method accepts any type of object as its parameters. These are evaluated relative to the project directory, as per the file() method, described in Section 18.1, “Locating files”. You can also pass collections, iterables, maps and arrays to the files() method. These are flattened and the contents converted to File instances.

Example 18.2. Creating a file collection

build.gradle

FileCollection collection = files('src/file1.txt',
                                  new File('src/file2.txt'),
                                  ['src/file3.txt', 'src/file4.txt'])

A file collection is iterable, and can be converted to a number of other types using the as operator. You can also add 2 file collections together using the + operator, or subtract one file collection from another using the - operator. Here are some examples of what you can do with a file collection.

Example 18.3. Using a file collection

build.gradle

// Iterate over the files in the collection
collection.each {File file ->
    println file.name
}

// Convert the collection to various types
Set set = collection.files
Set set2 = collection as Set
List list = collection as List
String path = collection.asPath
File file = collection.singleFile
File file2 = collection as File

// Add and subtract collections
def union = collection + files('src/file3.txt')
def different = collection - files('src/file3.txt')


You can also pass the files() method a closure or a Callable instance. This is called when the contents of the collection are queried, and its return value is converted to a set of File instances. The return value can be an object of any of the types supported by the files() method. This is a simple way to 'implement' the FileCollection interface.

Example 18.4. Implementing a file collection

build.gradle

task list << {
    File srcDir

    // Create a file collection using a closure
    collection = files { srcDir.listFiles() }

    srcDir = file('src')
    println "Contents of $srcDir.name"
    collection.collect { relativePath(it) }.sort().each { println it }

    srcDir = file('src2')
    println "Contents of $srcDir.name"
    collection.collect { relativePath(it) }.sort().each { println it }
}

Output of gradle -q list

> gradle -q list
Contents of src
src/dir1
src/file1.txt
Contents of src2
src2/dir1
src2/dir2

Some other types of things you can pass to files():

FileCollection

These are flattened and the contents included in the file collection.

Task

The output files of the task are included in the file collection.

TaskOutputs

The output files of the TaskOutputs are included in the file collection.

It is important to note that the content of a file collection is evaluated lazily, when it is needed. This means you can, for example, create a FileCollection that represents files which will be created in the future by, say, some task.

18.3. File trees

A file tree is a collection of files arranged in a hierarchy. For example, a file tree might represent a directory tree or the contents of a ZIP file. It is represented by the FileTree interface. The FileTree interface extends FileCollection, so you can treat a file tree exactly the same way as you would a file collection. Several objects in Gradle implement the FileTree interface, such as source sets.

One way to obtain a FileTree instance is to use the Project.fileTree(java.util.Map) method. This creates a FileTree defined with a base directory, and optionally some Ant-style include and exclude patterns.

Example 18.5. Creating a file tree

build.gradle

// Create a file tree with a base directory
FileTree tree = fileTree(dir: 'src/main')

// Add include and exclude patterns to the tree
tree.include '**/*.java'
tree.exclude '**/Abstract*'

// Create a tree using path
tree = fileTree('src').include('**/*.java')

// Create a tree using closure
tree = fileTree('src') {
    include '**/*.java'
}

// Create a tree using a map
tree = fileTree(dir: 'src', include: '**/*.java')
tree = fileTree(dir: 'src', includes: ['**/*.java', '**/*.xml'])
tree = fileTree(dir: 'src', include: '**/*.java', exclude: '**/*test*/**')

You use a file tree in the same way you use a file collection. You can also visit the contents of the tree, and select a sub-tree using Ant-style patterns:

Example 18.6. Using a file tree

build.gradle

// Iterate over the contents of a tree
tree.each {File file ->
    println file
}

// Filter a tree
FileTree filtered = tree.matching {
    include 'org/gradle/api/**'
}

// Add trees together
FileTree sum = tree + fileTree(dir: 'src/test')

// Visit the elements of the tree
tree.visit {element ->
    println "$element.relativePath => $element.file"
}

18.4. Using the contents of an archive as a file tree

You can use the contents of an archive, such as a ZIP or TAR file, as a file tree. You do this using the Project.zipTree(java.lang.Object) and Project.tarTree(java.lang.Object) methods. These methods return a FileTree instance which you can use like any other file tree or file collection. For example, you can use it to expand the archive by copying the contents, or to merge some archives into another.

Example 18.7. Using an archive as a file tree

build.gradle

// Create a ZIP file tree using path
FileTree zip = zipTree('someFile.zip')

// Create a TAR file tree using path
FileTree tar = tarTree('someFile.tar')

//tar tree attempts to guess the compression based on the file extension
//however if you must specify the compression explicitly you can:
FileTree someTar = tarTree(resources.gzip('someTar.ext'))


18.5. Specifying a set of input files

Many objects in Gradle have properties which accept a set of input files. For example, the JavaCompile task has a source property, which defines the source files to compile. You can set the value of this property using any of the types supported by the files() method, which was shown above. This means you can set the property using, for example, a File, String, collection, FileCollection or even a closure. Here are some examples:

Usually, there is a method with the same name as the property, which appends to the set of files. Again, this method accepts any of the types supported by the files() method.

Example 18.8. Specifying a set of files

build.gradle

task compile(type: JavaCompile)

// Use a File object to specify the source directory
compile {
    source = file('src/main/java')
}

// Use a String path to specify the source directory
compile {
    source = 'src/main/java'
}

// Use a collection to specify multiple source directories
compile {
    source = ['src/main/java', '../shared/java']
}

// Use a FileCollection (or FileTree in this case) to specify the source files
compile {
    source = fileTree(dir: 'src/main/java').matching { include 'org/gradle/api/**' }
}

// Using a closure to specify the source files.
compile {
    source = {
        // Use the contents of each zip file in the src dir
        file('src').listFiles().findAll {it.name.endsWith('.zip')}.collect { zipTree(it) }
    }
}

build.gradle

compile {
    // Add some source directories use String paths
    source 'src/main/java', 'src/main/groovy'

    // Add a source directory using a File object
    source file('../shared/java')

    // Add some source directories using a closure
    source { file('src/test/').listFiles() }
}

18.6. Copying files

You can use the Copy task to copy files. The copy task is very flexible, and allows you to, for example, filter the contents of the files as they are copied, and map to the file names.

To use the Copy task, you must provide a set of source files to copy, and a destination directory to copy the files to. You may also specify how to transform the files as they are copied. You do all this using a copy spec. A copy spec is represented by the CopySpec interface. The Copy task implements this interface. You specify the source files using the CopySpec.from(java.lang.Object[]) method. To specify the destination directory, use the CopySpec.into(java.lang.Object) method.

Example 18.9. Copying files using the copy task

build.gradle

task copyTask(type: Copy) {
    from 'src/main/webapp'
    into 'build/explodedWar'
}

The from() method accepts any of the arguments that the files() method does. When an argument resolves to a directory, everything under that directory (but not the directory itself) is recursively copied into the destination directory. When an argument resolves to a file, that file is copied into the destination directory. When an argument resolves to a non-existing file, that argument is ignored. If the argument is a task, the output files (i.e. the files the task creates) of the task are copied and the task is automatically added as a dependency of the Copy task. The into() accepts any of the arguments that the file() method does. Here is another example:

Example 18.10. Specifying copy task source files and destination directory

build.gradle

task anotherCopyTask(type: Copy) {
    // Copy everything under src/main/webapp
    from 'src/main/webapp'
    // Copy a single file
    from 'src/staging/index.html'
    // Copy the output of a task
    from copyTask
    // Copy the output of a task using Task outputs explicitly.
    from copyTaskWithPatterns.outputs
    // Copy the contents of a Zip file
    from zipTree('src/main/assets.zip')
    // Determine the destination directory later
    into { getDestDir() }
}

You can select the files to copy using Ant-style include or exclude patterns, or using a closure:

Example 18.11. Selecting the files to copy

build.gradle

task copyTaskWithPatterns(type: Copy) {
    from 'src/main/webapp'
    into 'build/explodedWar'
    include '**/*.html'
    include '**/*.jsp'
    exclude { details -> details.file.name.endsWith('.html') &&
                         details.file.text.contains('staging') }
}

You can also use the Project.copy(org.gradle.api.Action) method to copy files. It works the same way as the task with some major limitations though. First, the copy() is not incremental (see Section 17.9, “Skipping tasks that are up-to-date”).

Example 18.12. Copying files using the copy() method without up-to-date check

build.gradle

task copyMethod << {
    copy {
        from 'src/main/webapp'
        into 'build/explodedWar'
        include '**/*.html'
        include '**/*.jsp'
    }
}

Secondly, the copy() method can not honor task dependencies when a task is used as a copy source (i.e. as an argument to from()) because it's a method and not a task. As such, if you are using the copy() method as part of a task action, you must explicitly declare all inputs and outputs in order to get the correct behavior.

Example 18.13. Copying files using the copy() method with up-to-date check

build.gradle

task copyMethodWithExplicitDependencies{
    // up-to-date check for inputs, plus add copyTask as dependency
    inputs.file copyTask
    outputs.dir 'some-dir' // up-to-date check for outputs
    doLast{
        copy {
            // Copy the output of copyTask
            from copyTask
            into 'some-dir'
        }
    }
}

It is preferable to use the Copy task wherever possible, as it supports incremental building and task dependency inference without any extra effort on your part. The copy() method can be used to copy files as part of a task's implementation. That is, the copy method is intended to be used by custom tasks (see Chapter 38, Writing Custom Task Classes) that need to copy files as part of their function. In such a scenario, the custom task should sufficiently declare the inputs/outputs relevant to the copy action.

18.6.1. Renaming files

Example 18.14. Renaming files as they are copied

build.gradle

task rename(type: Copy) {
    from 'src/main/webapp'
    into 'build/explodedWar'
    // Use a closure to map the file name
    rename { String fileName ->
        fileName.replace('-staging-', '')
    }
    // Use a regular expression to map the file name
    rename '(.+)-staging-(.+)', '$1$2'
    rename(/(.+)-staging-(.+)/, '$1$2')
}

18.6.2. Filtering files

Example 18.15. Filtering files as they are copied

build.gradle

import org.apache.tools.ant.filters.FixCrLfFilter
import org.apache.tools.ant.filters.ReplaceTokens

task filter(type: Copy) {
    from 'src/main/webapp'
    into 'build/explodedWar'
    // Substitute property tokens in files
    expand(copyright: '2009', version: '2.3.1')
    expand(project.properties)
    // Use some of the filters provided by Ant
    filter(FixCrLfFilter)
    filter(ReplaceTokens, tokens: [copyright: '2009', version: '2.3.1'])
    // Use a closure to filter each line
    filter { String line ->
        "[$line]"
    }
    // Use a closure to remove lines
    filter { String line ->
        line.startsWith('-') ? null : line
    }
    filteringCharset = 'UTF-8'
}

When you use the ReplaceTokens class with the “filter” operation, the result is a template engine that replaces tokens of the form “@tokenName@” (the Apache Ant-style token) with a set of given values. The “expand” operation does the same thing except it treats the source files as Groovy templates in which tokens take the form “${tokenName}”. Be aware that you may need to escape parts of your source files when using this option, for example if it contains literal “$” or “<%” strings.

It's a good practice to specify the charset when reading and writing the file, using the filteringCharset property. If not specified, the JVM default charset is used, which might not match with the actual charset of the files to filter, and might be different from one machine to another.

18.6.3. Using the CopySpec class

Copy specs form a hierarchy. A copy spec inherits its destination path, include patterns, exclude patterns, copy actions, name mappings and filters.

Example 18.16. Nested copy specs

build.gradle

task nestedSpecs(type: Copy) {
    into 'build/explodedWar'
    exclude '**/*staging*'
    from('src/dist') {
        include '**/*.html'
    }
    into('libs') {
        from configurations.runtime
    }
}

18.7. Using the Sync task

The Sync task extends the Copy task. When it executes, it copies the source files into the destination directory, and then removes any files from the destination directory which it did not copy. This can be useful for doing things such as installing your application, creating an exploded copy of your archives, or maintaining a copy of the project's dependencies.

Here is an example which maintains a copy of the project's runtime dependencies in the build/libs directory.

Example 18.17. Using the Sync task to copy dependencies

build.gradle

task libs(type: Sync) {
    from configurations.runtime
    into "$buildDir/libs"
}

18.8. Creating archives

A project can have as many JAR archives as you want. You can also add WAR, ZIP and TAR archives to your project. Archives are created using the various archive tasks: Zip, Tar, Jar, War, and Ear. They all work the same way, so let's look at how you create a ZIP file.

Example 18.18. Creating a ZIP archive

build.gradle

apply plugin: 'java'

task zip(type: Zip) {
    from 'src/dist'
    into('libs') {
        from configurations.runtime
    }
}

Why are you using the Java plugin?

The Java plugin adds a number of default values for the archive tasks. You can use the archive tasks without using the Java plugin, if you like. You will need to provide values for some additional properties.

The archive tasks all work exactly the same way as the Copy task, and implement the same CopySpec interface. As with the Copy task, you specify the input files using the from() method, and can optionally specify where they end up in the archive using the into() method. You can filter the contents of file, rename files, and all the other things you can do with a copy spec.

18.8.1. Archive naming

The format of projectName-version.type is used for generated archive file names. For example:

Example 18.19. Creation of ZIP archive

build.gradle

apply plugin: 'java'

version = 1.0

task myZip(type: Zip) {
    from 'somedir'
}

println myZip.archiveName
println relativePath(myZip.destinationDir)
println relativePath(myZip.archivePath)

Output of gradle -q myZip

> gradle -q myZip
zipProject-1.0.zip
build/distributions
build/distributions/zipProject-1.0.zip

This adds a Zip archive task with the name myZip which produces ZIP file zipProject-1.0.zip. It is important to distinguish between the name of the archive task and the name of the archive generated by the archive task. The default name for archives can be changed with the archivesBaseName project property. The name of the archive can also be changed at any time later on.

There are a number of properties which you can set on an archive task. These are listed below in Table 18.1, “Archive tasks - naming properties”. You can, for example, change the name of the archive:

Example 18.20. Configuration of archive task - custom archive name

build.gradle

apply plugin: 'java'
version = 1.0

task myZip(type: Zip) {
    from 'somedir'
    baseName = 'customName'
}

println myZip.archiveName

Output of gradle -q myZip

> gradle -q myZip
customName-1.0.zip

You can further customize the archive names:

Example 18.21. Configuration of archive task - appendix & classifier

build.gradle

apply plugin: 'java'
archivesBaseName = 'gradle'
version = 1.0

task myZip(type: Zip) {
    appendix = 'wrapper'
    classifier = 'src'
    from 'somedir'
}

println myZip.archiveName

Output of gradle -q myZip

> gradle -q myZip
gradle-wrapper-1.0-src.zip

Table 18.1. Archive tasks - naming properties

Property name Type Default value Description
archiveName String baseName-appendix-version-classifier.extension

If any of these properties is empty the trailing - is not added to the name.

The base file name of the generated archive
archivePath File destinationDir/archiveName The absolute path of the generated archive.
destinationDir File Depends on the archive type. JARs and WARs go into project.buildDir/libraries. ZIPs and TARs go into project.buildDir/distributions. The directory to generate the archive into
baseName String project.name The base name portion of the archive file name.
appendix String null The appendix portion of the archive file name.
version String project.version The version portion of the archive file name.
classifier String null The classifier portion of the archive file name,
extension String Depends on the archive type, and for TAR files, the compression type as well: zip, jar, war, tar, tgz or tbz2. The extension of the archive file name.

18.8.2. Sharing content between multiple archives

You can use the Project.copySpec(org.gradle.api.Action) method to share content between archives.

Often you will want to publish an archive, so that it is usable from another project. This process is described in Chapter 30, Publishing artifacts

Chapter 19. Using Ant from Gradle

Gradle provides excellent integration with Ant. You can use individual Ant tasks or entire Ant builds in your Gradle builds. In fact, you will find that it's far easier and more powerful using Ant tasks in a Gradle build script, than it is to use Ant's XML format. You could even use Gradle simply as a powerful Ant task scripting tool.

Ant can be divided into two layers. The first layer is the Ant language. It provides the syntax for the build.xml file, the handling of the targets, special constructs like macrodefs, and so on. In other words, everything except the Ant tasks and types. Gradle understands this language, and allows you to import your Ant build.xml directly into a Gradle project. You can then use the targets of your Ant build as if they were Gradle tasks.

The second layer of Ant is its wealth of Ant tasks and types, like javac, copy or jar. For this layer Gradle provides integration simply by relying on Groovy, and the fantastic AntBuilder.

Finally, since build scripts are Groovy scripts, you can always execute an Ant build as an external process. Your build script may contain statements like:"ant clean compile".execute(). [8]

You can use Gradle's Ant integration as a path for migrating your build from Ant to Gradle. For example, you could start by importing your existing Ant build. Then you could move your dependency declarations from the Ant script to your build file. Finally, you could move your tasks across to your build file, or replace them with some of Gradle's plugins. This process can be done in parts over time, and you can have a working Gradle build during the entire process.

19.1. Using Ant tasks and types in your build

In your build script, a property called ant is provided by Gradle. This is a reference to an AntBuilder instance. This AntBuilder is used to access Ant tasks, types and properties from your build script. There is a very simple mapping from Ant's build.xml format to Groovy, which is explained below.

You execute an Ant task by calling a method on the AntBuilder instance. You use the task name as the method name. For example, you execute the Ant echo task by calling the ant.echo() method. The attributes of the Ant task are passed as Map parameters to the method. Below is an example of the echo task. Notice that we can also mix Groovy code and the Ant task markup. This can be extremely powerful.

Example 19.1. Using an Ant task

build.gradle

task hello << {
    String greeting = 'hello from Ant'
    ant.echo(message: greeting)
}

Output of gradle hello

> gradle hello
:hello
[ant:echo] hello from Ant

BUILD SUCCESSFUL

Total time: 1 secs

You pass nested text to an Ant task by passing it as a parameter of the task method call. In this example, we pass the message for the echo task as nested text:

Example 19.2. Passing nested text to an Ant task

build.gradle

task hello << {
    ant.echo('hello from Ant')
}

Output of gradle hello

> gradle hello
:hello
[ant:echo] hello from Ant

BUILD SUCCESSFUL

Total time: 1 secs

You pass nested elements to an Ant task inside a closure. Nested elements are defined in the same way as tasks, by calling a method with the same name as the element we want to define.

Example 19.3. Passing nested elements to an Ant task

build.gradle

task zip << {
    ant.zip(destfile: 'archive.zip') {
        fileset(dir: 'src') {
            include(name: '**.xml')
            exclude(name: '**.java')
        }
    }
}

You can access Ant types in the same way that you access tasks, using the name of the type as the method name. The method call returns the Ant data type, which you can then use directly in your build script. In the following example, we create an Ant path object, then iterate over the contents of it.

Example 19.4. Using an Ant type

build.gradle

task list << {
    def path = ant.path {
        fileset(dir: 'libs', includes: '*.jar')
    }
    path.list().each {
        println it
    }
}

More information about AntBuilder can be found in 'Groovy in Action' 8.4 or at the Groovy Wiki

19.1.1. Using custom Ant tasks in your build

To make custom tasks available in your build, you can use the taskdef (usually easier) or typedef Ant task, just as you would in a build.xml file. You can then refer to the custom Ant task as you would a built-in Ant task.

Example 19.5. Using a custom Ant task

build.gradle

task check << {
    ant.taskdef(resource: 'checkstyletask.properties') {
        classpath {
            fileset(dir: 'libs', includes: '*.jar')
        }
    }
    ant.checkstyle(config: 'checkstyle.xml') {
        fileset(dir: 'src')
    }
}

You can use Gradle's dependency management to assemble the classpath to use for the custom tasks. To do this, you need to define a custom configuration for the classpath, then add some dependencies to the configuration. This is described in more detail in Section 23.4, “How to declare your dependencies”.

Example 19.6. Declaring the classpath for a custom Ant task

build.gradle

configurations {
    pmd
}

dependencies {
    pmd group: 'pmd', name: 'pmd', version: '4.2.5'
}

To use the classpath configuration, use the asPath property of the custom configuration.

Example 19.7. Using a custom Ant task and dependency management together

build.gradle

task check << {
    ant.taskdef(name: 'pmd',
                classname: 'net.sourceforge.pmd.ant.PMDTask',
                classpath: configurations.pmd.asPath)
    ant.pmd(shortFilenames: 'true',
            failonruleviolation: 'true',
            rulesetfiles: file('pmd-rules.xml').toURI().toString()) {
        formatter(type: 'text', toConsole: 'true')
        fileset(dir: 'src')
    }
}

19.2. Importing an Ant build

You can use the ant.importBuild() method to import an Ant build into your Gradle project. When you import an Ant build, each Ant target is treated as a Gradle task. This means you can manipulate and execute the Ant targets in exactly the same way as Gradle tasks.

Example 19.8. Importing an Ant build

build.gradle

ant.importBuild 'build.xml'

build.xml

<project>
    <target name="hello">
        <echo>Hello, from Ant</echo>
    </target>
</project>

Output of gradle hello

> gradle hello
:hello
[ant:echo] Hello, from Ant

BUILD SUCCESSFUL

Total time: 1 secs

You can add a task which depends on an Ant target:

Example 19.9. Task that depends on Ant target

build.gradle

ant.importBuild 'build.xml'

task intro(dependsOn: hello) << {
    println 'Hello, from Gradle'
}

Output of gradle intro

> gradle intro
:hello
[ant:echo] Hello, from Ant
:intro
Hello, from Gradle

BUILD SUCCESSFUL

Total time: 1 secs

Or, you can add behaviour to an Ant target:

Example 19.10. Adding behaviour to an Ant target

build.gradle

ant.importBuild 'build.xml'

hello << {
    println 'Hello, from Gradle'
}

Output of gradle hello

> gradle hello
:hello
[ant:echo] Hello, from Ant
Hello, from Gradle

BUILD SUCCESSFUL

Total time: 1 secs

It is also possible for an Ant target to depend on a Gradle task:

Example 19.11. Ant target that depends on Gradle task

build.gradle

ant.importBuild 'build.xml'

task intro << {
    println 'Hello, from Gradle'
}

build.xml

<project>
    <target name="hello" depends="intro">
        <echo>Hello, from Ant</echo>
    </target>
</project>

Output of gradle hello

> gradle hello
:intro
Hello, from Gradle
:hello
[ant:echo] Hello, from Ant

BUILD SUCCESSFUL

Total time: 1 secs

Sometimes it may be necessary to “rename” the task generated for an Ant target to avoid a naming collision with existing Gradle tasks. To do this, use the AntBuilder.importBuild(java.lang.Object, org.gradle.api.Transformer) method.

Example 19.12. Renaming imported Ant targets

build.gradle

ant.importBuild('build.xml') { antTargetName ->
    'a-' + antTargetName
}

build.xml

<project>
    <target name="hello">
        <echo>Hello, from Ant</echo>
    </target>
</project>

Output of gradle a-hello

> gradle a-hello
:a-hello
[ant:echo] Hello, from Ant

BUILD SUCCESSFUL

Total time: 1 secs

Note that while the second argument to this method should be a Transformer, when programming in Groovy we can simply use a closure instead of an anonymous inner class (or similar) due to Groovy's support for automatically coercing closures to single-abstract-method types.

19.3. Ant properties and references

There are several ways to set an Ant property, so that the property can be used by Ant tasks. You can set the property directly on the AntBuilder instance. The Ant properties are also available as a Map which you can change. You can also use the Ant property task. Below are some examples of how to do this.

Example 19.13. Setting an Ant property

build.gradle

ant.buildDir = buildDir
ant.properties.buildDir = buildDir
ant.properties['buildDir'] = buildDir
ant.property(name: 'buildDir', location: buildDir)

build.xml

<echo>buildDir = ${buildDir}</echo>

Many Ant tasks set properties when they execute. There are several ways to get the value of these properties. You can get the property directly from the AntBuilder instance. The Ant properties are also available as a Map. Below are some examples.

Example 19.14. Getting an Ant property

build.xml

<property name="antProp" value="a property defined in an Ant build"/>

build.gradle

println ant.antProp
println ant.properties.antProp
println ant.properties['antProp']

There are several ways to set an Ant reference:

Example 19.15. Setting an Ant reference

build.gradle

ant.path(id: 'classpath', location: 'libs')
ant.references.classpath = ant.path(location: 'libs')
ant.references['classpath'] = ant.path(location: 'libs')

build.xml

<path refid="classpath"/>

There are several ways to get an Ant reference:

Example 19.16. Getting an Ant reference

build.xml

<path id="antPath" location="libs"/>

build.gradle

println ant.references.antPath
println ant.references['antPath']

19.4. Ant logging

Gradle maps Ant message priorities to Gradle log levels so that messages logged from Ant appear in the Gradle output. By default, these are mapped as follows:

Table 19.1. Ant message priority mapping

Ant Message Priority Gradle Log Level
VERBOSE DEBUG
DEBUG DEBUG
INFO INFO
WARN WARN
ERROR ERROR

19.4.1. Fine tuning Ant logging

The default mapping of Ant message priority to Gradle log level can sometimes be problematic. For example, there is no message priority that maps directly to the LIFECYCLE log level, which is the default for Gradle. Many Ant tasks log messages at the INFO priority, which means to expose those messages from Gradle, a build would have to be run with the log level set to INFO, potentially logging much more output than is desired.

Conversely, if an Ant task logs messages at too high of a level, to suppress those messages would require the build to be run at a higher log level, such as QUIET. However, this could result in other, desirable output being suppressed.

To help with this, Gradle allows the user to fine tune the Ant logging and control the mapping of message priority to Gradle log level. This is done by setting the priority that should map to the default Gradle LIFECYCLE log level using the AntBuilder.setLifecycleLogLevel(java.lang.String) method. When this value is set, any Ant message logged at the configured priority or above will be logged at least at LIFECYCLE. Any Ant message logged below this priority will be logged at most at INFO.

For example, the following changes the mapping such that Ant INFO priority messages are exposed at the LIFECYCLE log level.

Example 19.17. Fine tuning Ant logging

build.gradle

ant.lifecycleLogLevel = "INFO"

task hello {
    doLast {
        ant.echo(level: "info", message: "hello from info priority!")
    }
}

Output of gradle hello

> gradle hello
:hello
[ant:echo] hello from info priority!

BUILD SUCCESSFUL

Total time: 1 secs

On the other hand, if the lifecycleLogLevel was set to ERROR, Ant messages logged at the WARN priority would no longer be logged at the WARN log level. They would now be logged at the INFO level and would be suppressed by default.

19.5. API

The Ant integration is provided by AntBuilder.



[8] In Groovy you can execute Strings. To learn more about executing external processes with Groovy have a look in 'Groovy in Action' 9.3.2 or at the Groovy wiki

Chapter 20. The Build Lifecycle

We said earlier that the core of Gradle is a language for dependency based programming. In Gradle terms this means that you can define tasks and dependencies between tasks. Gradle guarantees that these tasks are executed in the order of their dependencies, and that each task is executed only once. These tasks form a Directed Acyclic Graph. There are build tools that build up such a dependency graph as they execute their tasks. Gradle builds the complete dependency graph before any task is executed. This lies at the heart of Gradle and makes many things possible which would not be possible otherwise.

Your build scripts configure this dependency graph. Therefore they are strictly speaking build configuration scripts.

20.1. Build phases

A Gradle build has three distinct phases.

Initialization

Gradle supports single and multi-project builds. During the initialization phase, Gradle determines which projects are going to take part in the build, and creates a Project instance for each of these projects.

Configuration

During this phase the project objects are configured. The build scripts of all projects which are part of the build are executed. Gradle 1.4 introduced an incubating opt-in feature called configuration on demand. In this mode, Gradle configures only relevant projects (see Section 24.1.1.1, “Configuration on demand”).

Execution

Gradle determines the subset of the tasks, created and configured during the configuration phase, to be executed. The subset is determined by the task name arguments passed to the gradle command and the current directory. Gradle then executes each of the selected tasks.

20.2. Settings file

Beside the build script files, Gradle defines a settings file. The settings file is determined by Gradle via a naming convention. The default name for this file is settings.gradle. Later in this chapter we explain how Gradle looks for a settings file.

The settings file is executed during the initialization phase. A multiproject build must have a settings.gradle file in the root project of the multiproject hierarchy. It is required because the settings file defines which projects are taking part in the multi-project build (see Chapter 24, Multi-project Builds). For a single-project build, a settings file is optional. Besides defining the included projects, you might need it to add libraries to your build script classpath (see Chapter 41, Organizing Build Logic). Let's first do some introspection with a single project build:

Example 20.1. Single project build

settings.gradle

println 'This is executed during the initialization phase.'

build.gradle

println 'This is executed during the configuration phase.'

task configured {
    println 'This is also executed during the configuration phase.'
}

task test << {
    println 'This is executed during the execution phase.'
}

task testBoth {
    doFirst {
      println 'This is executed first during the execution phase.'
    }
    doLast {
      println 'This is executed last during the execution phase.'
    }
    println 'This is executed during the configuration phase as well.'
}

Output of gradle test testBoth

> gradle test testBoth
This is executed during the initialization phase.
This is executed during the configuration phase.
This is also executed during the configuration phase.
This is executed during the configuration phase as well.
:test
This is executed during the execution phase.
:testBoth
This is executed first during the execution phase.
This is executed last during the execution phase.

BUILD SUCCESSFUL

Total time: 1 secs

For a build script, the property access and method calls are delegated to a project object. Similarly property access and method calls within the settings file is delegated to a settings object. Look at the Settings class in the API documentation for more information.

20.3. Multi-project builds

A multi-project build is a build where you build more than one project during a single execution of Gradle. You have to declare the projects taking part in the multiproject build in the settings file. There is much more to say about multi-project builds in the chapter dedicated to this topic (see Chapter 24, Multi-project Builds).

20.3.1. Project locations

Multi-project builds are always represented by a tree with a single root. Each element in the tree represents a project. A project has a path which denotes the position of the project in the multi-project build tree. In most cases the project path is consistent with the physical location of the project in the file system. However, this behavior is configurable. The project tree is created in the settings.gradle file. By default it is assumed that the location of the settings file is also the location of the root project. But you can redefine the location of the root project in the settings file.

20.3.2. Building the tree

In the settings file you can use a set of methods to build the project tree. Hierarchical and flat physical layouts get special support.

20.3.2.1. Hierarchical layouts

Example 20.2. Hierarchical layout

settings.gradle

include 'project1', 'project2:child', 'project3:child1'

The include method takes project paths as arguments. The project path is assumed to be equal to the relative physical file system path. For example, a path 'services:api' is mapped by default to a folder 'services/api' (relative from the project root). You only need to specify the leaves of the tree. This means that the inclusion of the path 'services:hotels:api' will result in creating 3 projects: 'services', 'services:hotels' and 'services:hotels:api'.

20.3.2.2. Flat layouts

Example 20.3. Flat layout

settings.gradle

includeFlat 'project3', 'project4'

The includeFlat method takes directory names as an argument. These directories need to exist as siblings of the root project directory. The location of these directories are considered as child projects of the root project in the multi-project tree.

20.3.3. Modifying elements of the project tree

The multi-project tree created in the settings file is made up of so called project descriptors. You can modify these descriptors in the settings file at any time. To access a descriptor you can do:

Using this descriptor you can change the name, project directory and build file of a project.

Example 20.4. Modification of elements of the project tree

settings.gradle

println rootProject.name
println project(':projectA').name

settings.gradle

rootProject.name = 'main'
project(':projectA').projectDir = new File(settingsDir, '../my-project-a')
project(':projectA').buildFileName = 'projectA.gradle'

Look at the ProjectDescriptor class in the API documentation for more information.

20.4. Initialization

How does Gradle know whether to do a single or multiproject build? If you trigger a multiproject build from a directory with a settings file, things are easy. But Gradle also allows you to execute the build from within any subproject taking part in the build. [9] If you execute Gradle from within a project with no settings.gradle file, Gradle looks for a settings.gradle file in the following way:

  • It looks in a directory called master which has the same nesting level as the current dir.

  • If not found yet, it searches parent directories.

  • If not found yet, the build is executed as a single project build.

  • If a settings.gradle file is found, Gradle checks if the current project is part of the multiproject hierarchy defined in the found settings.gradle file. If not, the build is executed as a single project build. Otherwise a multiproject build is executed.

What is the purpose of this behavior? Gradle needs to determine whether the project you are in is a subproject of a multiproject build or not. Of course, if it is a subproject, only the subproject and its dependent projects are built, but Gradle needs to create the build configuration for the whole multiproject build (see Chapter 24, Multi-project Builds). You can use the -u command line option to tell Gradle not to look in the parent hierarchy for a settings.gradle file. The current project is then always built as a single project build. If the current project contains a settings.gradle file, the -u option has no meaning. Such a build is always executed as:

  • a single project build, if the settings.gradle file does not define a multiproject hierarchy

  • a multiproject build, if the settings.gradle file does define a multiproject hierarchy.

The automatic search for a settings.gradle file only works for multi-project builds with a physical hierarchical or flat layout. For a flat layout you must additionally follow the naming convention described above (“master”). Gradle supports arbitrary physical layouts for a multiproject build, but for such arbitrary layouts you need to execute the build from the directory where the settings file is located. For information on how to run partial builds from the root see Section 24.4, “Running tasks by their absolute path”.

Gradle creates a Project object for every project taking part in the build. For a multi-project build these are the projects specified in the Settings object (plus the root project). Each project object has by default a name equal to the name of its top level directory, and every project except the root project has a parent project. Any project may have child projects.

20.5. Configuration and execution of a single project build

For a single project build, the workflow of the after initialization phases are pretty simple. The build script is executed against the project object that was created during the initialization phase. Then Gradle looks for tasks with names equal to those passed as command line arguments. If these task names exist, they are executed as a separate build in the order you have passed them. The configuration and execution for multi-project builds is discussed in Chapter 24, Multi-project Builds.

20.6. Responding to the lifecycle in the build script

Your build script can receive notifications as the build progresses through its lifecycle. These notifications generally take two forms: You can either implement a particular listener interface, or you can provide a closure to execute when the notification is fired. The examples below use closures. For details on how to use the listener interfaces, refer to the API documentation.

20.6.1. Project evaluation

You can receive a notification immediately before and after a project is evaluated. This can be used to do things like performing additional configuration once all the definitions in a build script have been applied, or for some custom logging or profiling.

Below is an example which adds a test task to each project which has a hasTests property value of true.

Example 20.5. Adding of test task to each project which has certain property set

build.gradle

allprojects {
    afterEvaluate { project ->
        if (project.hasTests) {
            println "Adding test task to $project"
            project.task('test') << {
                println "Running tests for $project"
            }
        }
    }
}

projectA.gradle

hasTests = true

Output of gradle -q test

> gradle -q test
Adding test task to project ':projectA'
Running tests for project ':projectA'

This example uses method Project.afterEvaluate() to add a closure which is executed after the project is evaluated.

It is also possible to receive notifications when any project is evaluated. This example performs some custom logging of project evaluation. Notice that the afterProject notification is received regardless of whether the project evaluates successfully or fails with an exception.

Example 20.6. Notifications

build.gradle

gradle.afterProject {project, projectState ->
    if (projectState.failure) {
        println "Evaluation of $project FAILED"
    } else {
        println "Evaluation of $project succeeded"
    }
}

Output of gradle -q test

> gradle -q test
Evaluation of root project 'buildProjectEvaluateEvents' succeeded
Evaluation of project ':projectA' succeeded
Evaluation of project ':projectB' FAILED

You can also add a ProjectEvaluationListener to the Gradle to receive these events.

20.6.2. Task creation

You can receive a notification immediately after a task is added to a project. This can be used to set some default values or add behaviour before the task is made available in the build file.

The following example sets the srcDir property of each task as it is created.

Example 20.7. Setting of certain property to all tasks

build.gradle

tasks.whenTaskAdded { task ->
    task.ext.srcDir = 'src/main/java'
}

task a

println "source dir is $a.srcDir"

Output of gradle -q a

> gradle -q a
source dir is src/main/java

You can also add an Action to a TaskContainer to receive these events.

20.6.3. Task execution graph ready

You can receive a notification immediately after the task execution graph has been populated. We have seen this already in Section 14.13, “Configure by DAG”.

You can also add a TaskExecutionGraphListener to the TaskExecutionGraph to receive these events.

20.6.4. Task execution

You can receive a notification immediately before and after any task is executed.

The following example logs the start and end of each task execution. Notice that the afterTask notification is received regardless of whether the task completes successfully or fails with an exception.

Example 20.8. Logging of start and end of each task execution

build.gradle

task ok

task broken(dependsOn: ok) << {
    throw new RuntimeException('broken')
}

gradle.taskGraph.beforeTask { Task task ->
    println "executing $task ..."
}

gradle.taskGraph.afterTask { Task task, TaskState state ->
    if (state.failure) {
        println "FAILED"
    }
    else {
        println "done"
    }
}

Output of gradle -q broken

> gradle -q broken
executing task ':ok' ...
done
executing task ':broken' ...
FAILED

You can also use a TaskExecutionListener to the TaskExecutionGraph to receive these events.



[9] Gradle supports partial multiproject builds (see Chapter 24, Multi-project Builds).

Chapter 21. Wrapper Plugin

The wrapper plugin is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The Gradle wrapper plugin allows the generation of Gradle wrapper files by adding a Wrapper task, that generates all files needed to run the build using the Gradle Wrapper. Details about the Gradle Wrapper can be found in Chapter 5, The Gradle Wrapper.

21.1. Usage

Without modifying the build.gradle file, the wrapper plugin can be auto-applied to the root project of the current build by running “gradle wrapper” from the command line. This applies the plugin if no task named wrapper is already defined in the build.

21.2. Tasks

The wrapper plugin adds the following tasks to the project:

Table 21.1. Wrapper plugin - tasks

Task name Depends on Type Description
wrapper - Wrapper Generates Gradle wrapper files.

Chapter 22. Logging

The log is the main 'UI' of a build tool. If it is too verbose, real warnings and problems are easily hidden by this. On the other hand you need relevant information for figuring out if things have gone wrong. Gradle defines 6 log levels, as shown in Table 22.1, “Log levels”. There are two Gradle-specific log levels, in addition to the ones you might normally see. Those levels are QUIET and LIFECYCLE. The latter is the default, and is used to report build progress.

Table 22.1. Log levels

Level Used for
ERROR Error messages
QUIET Important information messages
WARNING Warning messages
LIFECYCLE Progress information messages
INFO Information messages
DEBUG Debug messages

22.1. Choosing a log level

You can use the command line switches shown in Table 22.2, “Log level command-line options” to choose different log levels. In Table 22.3, “Stacktrace command-line options” you find the command line switches which affect stacktrace logging.

Table 22.2. Log level command-line options

Option Outputs Log Levels
no logging options LIFECYCLE and higher
-q or --quiet QUIET and higher
-i or --info INFO and higher
-d or --debug DEBUG and higher (that is, all log messages)

Table 22.3. Stacktrace command-line options

Option Meaning
No stacktrace options No stacktraces are printed to the console in case of a build error (e.g. a compile error). Only in case of internal exceptions will stacktraces be printed. If the DEBUG log level is chosen, truncated stacktraces are always printed.
-s or --stacktrace Truncated stacktraces are printed. We recommend this over full stacktraces. Groovy full stacktraces are extremely verbose (Due to the underlying dynamic invocation mechanisms. Yet they usually do not contain relevant information for what has gone wrong in your code.)
-S or --full-stacktrace The full stacktraces are printed out.

22.2. Writing your own log messages

A simple option for logging in your build file is to write messages to standard output. Gradle redirects anything written to standard output to it's logging system at the QUIET log level.

Example 22.1. Using stdout to write log messages

build.gradle

println 'A message which is logged at QUIET level'

Gradle also provides a logger property to a build script, which is an instance of Logger. This interface extends the SLF4J Logger interface and adds a few Gradle specific methods to it. Below is an example of how this is used in the build script:

Example 22.2. Writing your own log messages

build.gradle

logger.quiet('An info log message which is always logged.')
logger.error('An error log message.')
logger.warn('A warning log message.')
logger.lifecycle('A lifecycle info log message.')
logger.info('An info log message.')
logger.debug('A debug log message.')
logger.trace('A trace log message.')

You can also hook into Gradle's logging system from within other classes used in the build (classes from the buildSrc directory for example). Simply use an SLF4J logger. You can use this logger the same way as you use the provided logger in the build script.

Example 22.3. Using SLF4J to write log messages

build.gradle

import org.slf4j.Logger
import org.slf4j.LoggerFactory

Logger slf4jLogger = LoggerFactory.getLogger('some-logger')
slf4jLogger.info('An info log message logged using SLF4j')

22.3. Logging from external tools and libraries

Internally, Gradle uses Ant and Ivy. Both have their own logging system. Gradle redirects their logging output into the Gradle logging system. There is a 1:1 mapping from the Ant/Ivy log levels to the Gradle log levels, except the Ant/Ivy TRACE log level, which is mapped to Gradle DEBUG log level. This means the default Gradle log level will not show any Ant/Ivy output unless it is an error or a warning.

There are many tools out there which still use standard output for logging. By default, Gradle redirects standard output to the QUIET log level and standard error to the ERROR level. This behavior is configurable. The project object provides a LoggingManager, which allows you to change the log levels that standard out or error are redirected to when your build script is evaluated.

Example 22.4. Configuring standard output capture

build.gradle

logging.captureStandardOutput LogLevel.INFO
println 'A message which is logged at INFO level'

To change the log level for standard out or error during task execution, tasks also provide a LoggingManager.

Example 22.5. Configuring standard output capture for a task

build.gradle

task logInfo {
    logging.captureStandardOutput LogLevel.INFO
    doFirst {
        println 'A task message which is logged at INFO level'
    }
}

Gradle also provides integration with the Java Util Logging, Jakarta Commons Logging and Log4j logging toolkits. Any log messages which your build classes write using these logging toolkits will be redirected to Gradle's logging system.

22.4. Changing what Gradle logs

You can replace much of Gradle's logging UI with your own. You might do this, for example, if you want to customize the UI in some way - to log more or less information, or to change the formatting. You replace the logging using the Gradle.useLogger(java.lang.Object) method. This is accessible from a build script, or an init script, or via the embedding API. Note that this completely disables Gradle's default output. Below is an example init script which changes how task execution and build completion is logged.

Example 22.6. Customizing what Gradle logs

init.gradle

useLogger(new CustomEventLogger())

class CustomEventLogger extends BuildAdapter implements TaskExecutionListener {

    public void beforeExecute(Task task) {
        println "[$task.name]"
    }

    public void afterExecute(Task task, TaskState state) {
        println()
    }
    
    public void buildFinished(BuildResult result) {
        println 'build completed'
        if (result.failure != null) {
            result.failure.printStackTrace()
        }
    }
}

Output of gradle -I init.gradle build

> gradle -I init.gradle build
[compile]
compiling source

[testCompile]
compiling test source

[test]
running unit tests

[build]

build completed

Your logger can implement any of the listener interfaces listed below. When you register a logger, only the logging for the interfaces that it implements is replaced. Logging for the other interfaces is left untouched. You can find out more about the listener interfaces in Section 20.6, “Responding to the lifecycle in the build script”.

Chapter 23. Dependency Management

23.1. Introduction

Dependency management is a critical feature of every build, and Gradle has placed an emphasis on offering first-class dependency management that is both easy to understand and compatible with a wide variety of approaches. If you are familiar with the approach used by either Maven or Ivy you will be delighted to learn that Gradle is fully compatible with both approaches in addition to being flexible enough to support fully-customized approaches.

Here are the major highlights of Gradle's support for dependency management:

  • Transitive dependency management: Gradle gives you full control of your project's dependency tree.

  • Support for non-managed dependencies: If your dependencies are simply files in version control or a shared drive, Gradle provides powerful functionality to support this.

  • Support for custom dependency definitions.: Gradle's Module Dependencies give you the ability to describe the dependency hierarchy in the build script.

  • A fully customizable approach to Dependency Resolution: Gradle provides you with the ability to customize resolution rules making dependency substitution easy.

  • Full Compatibility with Maven and Ivy: If you have defined dependencies in a Maven POM or an Ivy file, Gradle provides seamless integration with a range of popular build tools.

  • Integration with existing dependency management infrastructure: Gradle is compatible with both Maven and Ivy repositories. If you use Archiva, Nexus, or Artifactory, Gradle is 100% compatible with all repository formats.

With hundreds of thousands of interdependent open source components each with a range of versions and incompatibilities, dependency management has a habit of causing problems as builds grow in complexity. When a build's dependency tree becomes unwieldy, your build tool shouldn't force you to adopt a single, inflexible approach to dependency management. A proper build system has to be designed to be flexible, and Gradle can handle any situation.

23.1.1. Flexible dependency management for migrations

Dependency management can be particularly challenging during a migration from one build system to another. If you are migrating from a tool like Ant or Maven to Gradle, you may be faced with some difficult situations. For example, one common pattern is an Ant project with version-less jar files stored in the filesystem. Other build systems require a wholesale replacement of this approach before migrating. With Gradle, you can adapt your new build to any existing source of dependencies or dependency metadata. This makes incremental migration to Gradle much easier than the alternative. On most large projects, build migrations and any change to development process is incremental because most organizations can't afford to stop everything and migrate to a build tool's idea of dependency management.

Even if your project is using a custom dependency management system or something like an Eclipse .classpath file as master data for dependency management, it is very easy to write a Gradle plugin to use this data in Gradle. For migration purposes this is a common technique with Gradle. (But, once you've migrated, it might be a good idea to move away from a .classpath file and use Gradle's dependency management features directly.)

23.1.2. Dependency management and Java

It is ironic that in a language known for its rich library of open source components that Java has no concept of libraries or versions. In Java, there is no standard way to tell the JVM that you are using version 3.0.5 of Hibernate, and there is no standard way to say that foo-1.0.jar depends on bar-2.0.jar. This has led to external solutions often based on build tools. The most popular ones at the moment are Maven and Ivy. While Maven provides a complete build system, Ivy focuses solely on dependency management.

Both tools rely on descriptor XML files, which contain information about the dependencies of a particular jar. Both also use repositories where the actual jars are placed together with their descriptor files, and both offer resolution for conflicting jar versions in one form or the other. Both have emerged as standards for solving dependency conflicts, and while Gradle originally used Ivy under the hood for its dependency management. Gradle has replaced this direct dependency on Ivy with a native Gradle dependency resolution engine which supports a range of approaches to dependency resolution including both POM and Ivy descriptor files.

23.2. Dependency Management Best Practices

While Gradle has strong opinions on dependency management, the tool gives you a choice between two options: follow recommended best practices or support any kind of pattern you can think of. This section outlines the Gradle project's recommended best practices for managing dependencies.

No matter what the language, proper dependency management is important for every project. From a complex enterprise application written in Java depending on hundreds of open source libraries to the simplest Clojure application depending on a handful of libraries, approaches to dependency management vary widely and can depend on the target technology, the method of application deployment, and the nature of the project. Projects bundled as reusable libraries may have different requirements than enterprise applications integrated into much larger systems of software and infrastructure. Despite this wide variation of requirements, the Gradle project recommends that all projects follow this set of core rules:

23.2.1. Put the Version in the Filename (Version the jar)

The version of a library must be part of the filename. While the version of a jar is usually in the Manifest file, it isn't readily apparent when you are inspecting a project. If someone asks you to look at a collection of 20 jar files, which would you prefer? A collection of files with names like commons-beanutils-1.3.jar or a collection of files with names like spring.jar? If dependencies have file names with version numbers you can quickly identify the versions of your dependencies.

If versions are unclear you can introduce subtle bugs which are very hard to find. For example there might be a project which uses Hibernate 2.5. Think about a developer who decides to install version 3.0.5 of Hibernate on her machine to fix a critical security bug but forgets to notify others in the team of this change. She may address the security bug successfully, but she also may have introduced subtle bugs into a codebase that was using a now-deprecated feature from Hibernate. Weeks later there is an exception on the integration machine which can't be reproduced on anyone's machine. Multiple developers then spend days on this issue only finally realising that the error would have easy to uncover if they knew that Hibernate had been upgraded from 2.5 to 3.0.5.

Versions in jar names increase the expressiveness of your project and make them easier to maintain. This practice also reduces the potential for error.

23.2.2. Manage transitive dependencies

Transitive dependency management is a technique that enables your project to depend on libraries which, in turn, depend on other libraries. This recursive pattern of transitive dependencies results in a tree of dependencies including your project's first-level dependencies, second-level dependencies, and so on. If you don't model your dependencies as a hierarchical tree of first-level and second-level dependencies it is very easy to quickly lose control over an assembled mess of unstructured dependencies. Consider the Gradle project itself, while Gradle only has a few direct, first-level dependencies, when Gradle is compiled it needs more than one hundred dependencies on the classpath. On a far larger scale, Enterprise projects using Spring, Hibernate, and other libraries, alongside hundreds or thousands of internal projects, can result in very large dependency trees.

When these large dependency trees need to change, you'll often have to solve some dependency version conflicts. Say one open source library needs one version of a logging library and a another uses an alternative version. Gradle and other build tools all have the ability to resolve conflicts, but what differentiates Gradle is the control it gives you over transitive dependencies and conflict resolution.

While you could try to manage this problem manually, you will quickly find that this approach doesn't scale. If you want to get rid of a first level dependency you really can't be sure which other jars you should remove. A dependency of a first level dependency might also be a first level dependency itself, or it might be a transitive dependency of yet another first level dependency. If you try to manage transitive dependencies yourself, the end of the story is that your build becomes brittle: no one dares to change your dependencies because the risk of breaking the build is too high. The project classpath becomes a complete mess, and, if a classpath problem arises, hell on earth invites you for a ride.

NOTE:In one project, we found a mystery LDAP related jar in the classpath. No code referenced this jar and there was no connection to the project. No one could figure out what the jar was for, until it was removed from the build and the application suffered massive performance problems whenever it attempted to authenticate to LDAP. This mystery jar was a necessary transitive, fourth-level dependency that was easy to miss because no one had bothered to use managed transitive dependencies.

Gradle offers you different ways to express first-level and transitive dependencies. With Gradle you can mix and match approaches; for example, you could store your jars in an SCM without XML descriptor files and still use transitive dependency management.

23.2.3. Resolve version conflicts

Conflicting versions of the same jar should be detected and either resolved or cause an exception. If you don't use transitive dependency management, version conflicts are undetected and the often accidental order of the classpath will determine what version of a dependency will win. On a large project with many developers changing dependencies, successful builds will be few and far between as the order of dependencies may directly affect whether a build succeeds or fails (or whether a bug appears or disappears in production).

If you haven't had to deal with the curse of conflicting versions of jars on a classpath, here is a small anecdote of the fun that awaits you. In a large project with 30 submodules, adding a dependency to a subproject changed the order of a classpath, swapping Spring 2.5 for an older 2.4 version. While the build continued to work, developers were starting to notice all sorts of surprising (and surprisingly awful) bugs in production. Worse yet, this unintentional downgrade of Spring introduced several security vulnerabilities into the system, which now required a full security audit throughout the organization.

In short, version conflicts are bad, and you should manage your transitive dependencies to avoid them. You might also want to learn where conflicting versions are used and consolidate on a particular version of a dependency across your organization. With a good conflict reporting tool like Gradle, that information can be used to communicate with the entire organization and standardize on a single version. If you think version conflicts don't happen to you, think again. It is very common for different first-level dependencies to rely on a range of different overlapping versions for other dependencies, and the JVM doesn't yet offer an easy way to have different versions of the same jar in the classpath (see Section 23.1.2, “Dependency management and Java”).

Gradle offers the following conflict resolution strategies:

  • Newest: The newest version of the dependency is used. This is Gradle's default strategy, and is often an appropriate choice as long as versions are backwards-compatible.
  • Fail: A version conflict results in a build failure. This strategy requires all version conflicts to be resolved explicitly in the build script. See ResolutionStrategy for details on how to explicitly choose a particular version.

While the strategies introduced above are usually enough to solve most conflicts, Gradle provides more fine-grained mechanisms to resolve version conflicts:

  • Configuring a first level dependency as forced. This approach is useful if the dependency in conflict is already a first level dependency. See examples in DependencyHandler.
  • Configuring any dependency (transitive or not) as forced. This approach is useful if the dependency in conflict is a transitive dependency. It also can be used to force versions of first level dependencies. See examples in ResolutionStrategy
  • Dependency resolve rules are an incubating feature introduced in Gradle 1.4 which give you fine-grained control over the version selected for a particular dependency.

To deal with problems due to version conflicts, reports with dependency graphs are also very helpful. Such reports are another feature of dependency management.

23.2.4. Use Dynamic Versions and Changing Modules

There are many situations when you want to use the latest version of a particular dependency, or the latest in a range of versions. This can be a requirement during development, or you may be developing a library that is designed to work with a range of dependency versions. You can easily depend on these constantly changing dependencies by using a dynamic version. A dynamic version can be either a version range (e.g. 2.+) or it can be a placeholder for the latest version available (e.g. latest.integration).

Alternatively, sometimes the module you request can change over time, even for the same version. An example of this type of changing module is a Maven SNAPSHOT module, which always points at the latest artifact published. In other words, a standard Maven snapshot is a module that never stands still so to speak, it is a “changing module”.

The main difference between a dynamic version and a changing module is that when you resolve a dynamic version, you'll get the real, static version as the module name. When you resolve a changing module, the artifacts are named using the version you requested, but the underlying artifacts may change over time.

By default, Gradle caches dynamic versions and changing modules for 24 hours. You can override the default cache modes using command line options. You can change the cache expiry times in your build using the resolution strategy (see Section 23.9.3, “Fine-tuned control over dependency caching”).

23.3. Dependency configurations

In Gradle dependencies are grouped into configurations. Configurations have a name, a number of other properties, and they can extend each other. Many Gradle plugins add pre-defined configurations to your project. The Java plugin, for example, adds some configurations to represent the various classpaths it needs. see Section 45.5, “Dependency management” for details. Of course you can add custom configurations on top of that. There are many use cases for custom configurations. This is very handy for example for adding dependencies not needed for building or testing your software (e.g. additional JDBC drivers to be shipped with your distribution).

A project's configurations are managed by a configurations object. The closure you pass to the configurations object is applied against its API. To learn more about this API have a look at ConfigurationContainer.

To define a configuration:

Example 23.1. Definition of a configuration

build.gradle

configurations {
    compile
}

To access a configuration:

Example 23.2. Accessing a configuration

build.gradle

println configurations.compile.name
println configurations['compile'].name

To configure a configuration:

Example 23.3. Configuration of a configuration

build.gradle

configurations {
    compile {
        description = 'compile classpath'
        transitive = true
    }
    runtime {
        extendsFrom compile
    }
}
configurations.compile {
    description = 'compile classpath'
}

23.4. How to declare your dependencies

There are several different types of dependencies that you can declare:

Table 23.1. Dependency types

Type Description
External module dependency A dependency on an external module in some repository.
Project dependency A dependency on another project in the same build.
File dependency A dependency on a set of files on the local filesystem.
Client module dependency A dependency on an external module, where the artifacts are located in some repository but the module meta-data is specified by the local build. You use this kind of dependency when you want to override the meta-data for the module.
Gradle API dependency A dependency on the API of the current Gradle version. You use this kind of dependency when you are developing custom Gradle plugins and task types.
Local Groovy dependency A dependency on the Groovy version used by the current Gradle version. You use this kind of dependency when you are developing custom Gradle plugins and task types.

23.4.1. External module dependencies

External module dependencies are the most common dependencies. They refer to a module in an external repository.

Example 23.4. Module dependencies

build.gradle

dependencies {
    runtime group: 'org.springframework', name: 'spring-core', version: '2.5'
    runtime 'org.springframework:spring-core:2.5',
            'org.springframework:spring-aop:2.5'
    runtime(
        [group: 'org.springframework', name: 'spring-core', version: '2.5'],
        [group: 'org.springframework', name: 'spring-aop', version: '2.5']
    )
    runtime('org.hibernate:hibernate:3.0.5') {
        transitive = true
    }
    runtime group: 'org.hibernate', name: 'hibernate', version: '3.0.5', transitive: true
    runtime(group: 'org.hibernate', name: 'hibernate', version: '3.0.5') {
        transitive = true
    }
}

See the DependencyHandler class in the API documentation for more examples and a complete reference.

Gradle provides different notations for module dependencies. There is a string notation and a map notation. A module dependency has an API which allows further configuration. Have a look at ExternalModuleDependency to learn all about the API. This API provides properties and configuration methods. Via the string notation you can define a subset of the properties. With the map notation you can define all properties. To have access to the complete API, either with the map or with the string notation, you can assign a single dependency to a configuration together with a closure.

If you declare a module dependency, Gradle looks for a module descriptor file (pom.xml or ivy.xml) in the repositories. If such a module descriptor file exists, it is parsed and the artifacts of this module (e.g. hibernate-3.0.5.jar) as well as its dependencies (e.g. cglib) are downloaded. If no such module descriptor file exists, Gradle looks for a file called hibernate-3.0.5.jar to retrieve. In Maven, a module can have one and only one artifact. In Gradle and Ivy, a module can have multiple artifacts. Each artifact can have a different set of dependencies.

23.4.1.1. Depending on modules with multiple artifacts

As mentioned earlier, a Maven module has only one artifact. Hence, when your project depends on a Maven module, it's obvious what its artifact is. With Gradle or Ivy, the case is different. Ivy's dependency descriptor (ivy.xml) can declare multiple artifacts. For more information, see the Ivy reference for ivy.xml. In Gradle, when you declare a dependency on an Ivy module, you actually declare a dependency on the default configuration of that module. So the actual set of artifacts (typically jars) you depend on is the set of artifacts that are associated with the default configuration of that module. Here are some situations where this matters:
  • The default configuration of a module contains undesired artifacts. Rather than depending on the whole configuration, a dependency on just the desired artifacts is declared.
  • The desired artifact belongs to a configuration other than default. That configuration is explicitly named as part of the dependency declaration.
There are other situations where it is necessary to fine-tune dependency declarations. Please see the DependencyHandler class in the API documentation for examples and a complete reference for declaring dependencies.

23.4.1.2. Artifact only notation

As said above, if no module descriptor file can be found, Gradle by default downloads a jar with the name of the module. But sometimes, even if the repository contains module descriptors, you want to download only the artifact jar, without the dependencies. [10] And sometimes you want to download a zip from a repository, that does not have module descriptors. Gradle provides an artifact only notation for those use cases - simply prefix the extension that you want to be downloaded with '@' sign:

Example 23.5. Artifact only notation

build.gradle

dependencies {
    runtime "org.groovy:groovy:2.2.0@jar"
    runtime group: 'org.groovy', name: 'groovy', version: '2.2.0', ext: 'jar'
}


An artifact only notation creates a module dependency which downloads only the artifact file with the specified extension. Existing module descriptors are ignored.

23.4.1.3. Classifiers

The Maven dependency management has the notion of classifiers. [11] Gradle supports this. To retrieve classified dependencies from a Maven repository you can write:

Example 23.6. Dependency with classifier

build.gradle

compile "org.gradle.test.classifiers:service:1.0:jdk15@jar"
otherConf group: 'org.gradle.test.classifiers', name: 'service', version: '1.0', classifier: 'jdk14'

As can be seen in the first line above, classifiers can be used together with the artifact only notation.

It is easy to iterate over the dependency artifacts of a configuration:

Example 23.7. Iterating over a configuration

build.gradle

task listJars << {
    configurations.compile.each { File file -> println file.name }
}

Output of gradle -q listJars

> gradle -q listJars
hibernate-core-3.6.7.Final.jar
antlr-2.7.6.jar
commons-collections-3.1.jar
dom4j-1.6.1.jar
hibernate-commons-annotations-3.2.0.Final.jar
hibernate-jpa-2.0-api-1.0.1.Final.jar
jta-1.1.jar
slf4j-api-1.6.1.jar

23.4.2. Client module dependencies

Client module dependencies allow you to declare transitive dependencies directly in the build script. They are a replacement for a module descriptor in an external repository.

Example 23.8. Client module dependencies - transitive dependencies

build.gradle

dependencies {
    runtime module("org.codehaus.groovy:groovy:2.4.4") {
        dependency("commons-cli:commons-cli:1.0") {
            transitive = false
        }
        module(group: 'org.apache.ant', name: 'ant', version: '1.9.6') {
            dependencies "org.apache.ant:ant-launcher:1.9.6@jar",
                         "org.apache.ant:ant-junit:1.9.6"
        }
    }
}

This declares a dependency on Groovy. Groovy itself has dependencies. But Gradle does not look for an XML descriptor to figure them out but gets the information from the build file. The dependencies of a client module can be normal module dependencies or artifact dependencies or another client module. Also look at the API documentation for the ClientModule class.

In the current release client modules have one limitation. Let's say your project is a library and you want this library to be uploaded to your company's Maven or Ivy repository. Gradle uploads the jars of your project to the company repository together with the XML descriptor file of the dependencies. If you use client modules the dependency declaration in the XML descriptor file is not correct. We will improve this in a future release of Gradle.

23.4.3. Project dependencies

Gradle distinguishes between external dependencies and dependencies on projects which are part of the same multi-project build. For the latter you can declare Project Dependencies.

Example 23.9. Project dependencies

build.gradle

dependencies {
    compile project(':shared')
}

For more information see the API documentation for ProjectDependency.

Multi-project builds are discussed in Chapter 24, Multi-project Builds.

23.4.4. File dependencies

File dependencies allow you to directly add a set of files to a configuration, without first adding them to a repository. This can be useful if you cannot, or do not want to, place certain files in a repository. Or if you do not want to use any repositories at all for storing your dependencies.

To add some files as a dependency for a configuration, you simply pass a file collection as a dependency:

Example 23.10. File dependencies

build.gradle

dependencies {
    runtime files('libs/a.jar', 'libs/b.jar')
    runtime fileTree(dir: 'libs', include: '*.jar')
}

File dependencies are not included in the published dependency descriptor for your project. However, file dependencies are included in transitive project dependencies within the same build. This means they cannot be used outside the current build, but they can be used with the same build.

You can declare which tasks produce the files for a file dependency. You might do this when, for example, the files are generated by the build.

Example 23.11. Generated file dependencies

build.gradle

dependencies {
    compile files("$buildDir/classes") {
        builtBy 'compile'
    }
}

task compile << {
    println 'compiling classes'
}

task list(dependsOn: configurations.compile) << {
    println "classpath = ${configurations.compile.collect {File file -> file.name}}"
}

Output of gradle -q list

> gradle -q list
compiling classes
classpath = [classes]

23.4.5. Gradle API Dependency

You can declare a dependency on the API of the current version of Gradle by using the DependencyHandler.gradleApi() method. This is useful when you are developing custom Gradle tasks or plugins.

Example 23.12. Gradle API dependencies

build.gradle

dependencies {
    compile gradleApi()
}

23.4.6. Local Groovy Dependency

You can declare a dependency on the Groovy that is distributed with Gradle by using the DependencyHandler.localGroovy() method. This is useful when you are developing custom Gradle tasks or plugins in Groovy.

Example 23.13. Gradle's Groovy dependencies

build.gradle

dependencies {
    compile localGroovy()
}

23.4.7. Excluding transitive dependencies

You can exclude a transitive dependency either by configuration or by dependency:

Example 23.14. Excluding transitive dependencies

build.gradle

configurations {
    compile.exclude module: 'commons'
    all*.exclude group: 'org.gradle.test.excludes', module: 'reports'
}

dependencies {
    compile("org.gradle.test.excludes:api:1.0") {
        exclude module: 'shared'
    }
}

If you define an exclude for a particular configuration, the excluded transitive dependency will be filtered for all dependencies when resolving this configuration or any inheriting configuration. If you want to exclude a transitive dependency from all your configurations you can use the Groovy spread-dot operator to express this in a concise way, as shown in the example. When defining an exclude, you can specify either only the organization or only the module name or both. Also look at the API documentation of the Dependency and Configuration classes.

Not every transitive dependency can be excluded - some transitive dependencies might be essential for correct runtime behavior of the application. Generally, one can exclude transitive dependencies that are either not required by runtime or that are guaranteed to be available on the target environment/platform.

Should you exclude per-dependency or per-configuration? It turns out that in the majority of cases you want to use the per-configuration exclusion. Here are some typical reasons why one might want to exclude a transitive dependency. Bear in mind that for some of these use cases there are better solutions than exclusions!

  • The dependency is undesired due to licensing reasons.
  • The dependency is not available in any remote repositories.
  • The dependency is not needed for runtime.
  • The dependency has a version that conflicts with a desired version. For that use case please refer to Section 23.2.3, “Resolve version conflicts” and the documentation on ResolutionStrategy for a potentially better solution to the problem.

Basically, in most of the cases excluding the transitive dependency should be done per configuration. This way the dependency declaration is more explicit. It is also more accurate because a per-dependency exclude rule does not guarantee the given transitive dependency does not show up in the configuration. For example, some other dependency, which does not have any exclude rules, might pull in that unwanted transitive dependency.

Other examples of dependency exclusions can be found in the reference for the ModuleDependency or DependencyHandler classes.

23.4.8. Optional attributes

All attributes for a dependency are optional, except the name. Which attributes are required for actually finding dependencies in the repository will depend on the repository type. See Section 23.6, “Repositories”. For example, if you work with Maven repositories, you need to define the group, name and version. If you work with filesystem repositories you might only need the name or the name and the version.

Example 23.15. Optional attributes of dependencies

build.gradle

dependencies {
    runtime ":junit:4.12", ":testng"
    runtime name: 'testng'
}

You can also assign collections or arrays of dependency notations to a configuration:

Example 23.16. Collections and arrays of dependencies

build.gradle

List groovy = ["org.codehaus.groovy:groovy-all:2.4.4@jar",
               "commons-cli:commons-cli:1.0@jar",
               "org.apache.ant:ant:1.9.6@jar"]
List hibernate = ['org.hibernate:hibernate:3.0.5@jar',
                  'somegroup:someorg:1.0@jar']
dependencies {
    runtime groovy, hibernate
}

23.4.9. Dependency configurations

In Gradle a dependency can have different configurations (as your project can have different configurations). If you don't specify anything explicitly, Gradle uses the default configuration of the dependency. For dependencies from a Maven repository, the default configuration is the only possibility anyway. If you work with Ivy repositories and want to declare a non-default configuration for your dependency you have to use the map notation and declare:

Example 23.17. Dependency configurations

build.gradle

dependencies {
    runtime group: 'org.somegroup', name: 'somedependency', version: '1.0', configuration: 'someConfiguration'
}

To do the same for project dependencies you need to declare:

Example 23.18. Dependency configurations for project

build.gradle

dependencies {
    compile project(path: ':api', configuration: 'spi')
}

23.4.10. Dependency reports

You can generate dependency reports from the command line (see Section 4.7.4, “Listing project dependencies”). With the help of the Project report plugin (see Chapter 27, The Project Report Plugin) such a report can be created by your build.

Since Gradle 1.2 there is also a new programmatic API to access the resolved dependency information. The dependency reports (see the previous paragraph) are using this API under the covers. The API lets you walk the resolved dependency graph and provides information about the dependencies. In future releases the API will grow to provide more information about the resolution result. For more information about the API please refer to the Javadocs on ResolvableDependencies.getResolutionResult(). Potential usages of the ResolutionResult API:

  • Creation of advanced dependency reports tailored to your use case.
  • Enabling the build logic to make decisions based on the content of the dependency graph.

23.5. Working with dependencies

For the examples below we have the following dependencies setup:

Example 23.19. Configuration.copy

build.gradle

configurations {
    sealife
    alllife
}

dependencies {
    sealife "sea.mammals:orca:1.0", "sea.fish:shark:1.0", "sea.fish:tuna:1.0"
    alllife configurations.sealife
    alllife "air.birds:albatross:1.0"
}

The dependencies have the following transitive dependencies:

shark-1.0 -> seal-2.0, tuna-1.0

orca-1.0 -> seal-1.0

tuna-1.0 -> herring-1.0

You can use the configuration to access the declared dependencies or a subset of those:

Example 23.20. Accessing declared dependencies

build.gradle

task dependencies << {
    configurations.alllife.dependencies.each { dep -> println dep.name }
    println()
    configurations.alllife.allDependencies.each { dep -> println dep.name }
    println()
    configurations.alllife.allDependencies.findAll { dep -> dep.name != 'orca' }
        .each { dep -> println dep.name }
}

Output of gradle -q dependencies

> gradle -q dependencies
albatross

albatross
orca
shark
tuna

albatross
shark
tuna

The dependencies task returns only the dependencies belonging explicitly to the configuration. The allDependencies task includes the dependencies from extended configurations.

To get the library files of the configuration dependencies you can do:

Example 23.21. Configuration.files

build.gradle

task allFiles << {
    configurations.sealife.files.each { file ->
        println file.name
    }
}

Output of gradle -q allFiles

> gradle -q allFiles
orca-1.0.jar
shark-1.0.jar
tuna-1.0.jar
herring-1.0.jar
seal-2.0.jar

Sometimes you want the library files of a subset of the configuration dependencies (e.g. of a single dependency).

Example 23.22. Configuration.files with spec

build.gradle

task files << {
    configurations.sealife.files { dep -> dep.name == 'orca' }.each { file ->
        println file.name
    }
}

Output of gradle -q files

> gradle -q files
orca-1.0.jar
seal-2.0.jar

The Configuration.files method always retrieves all artifacts of the whole configuration. It then filters the retrieved files by specified dependencies. As you can see in the example, transitive dependencies are included.

You can also copy a configuration. You can optionally specify that only a subset of dependencies from the original configuration should be copied. The copying methods come in two flavors. The copy method copies only the dependencies belonging explicitly to the configuration. The copyRecursive method copies all the dependencies, including the dependencies from extended configurations.

Example 23.23. Configuration.copy

build.gradle

task copy << {
    configurations.alllife.copyRecursive { dep -> dep.name != 'orca' }
        .allDependencies.each { dep -> println dep.name }
    println()
    configurations.alllife.copy().allDependencies
        .each { dep -> println dep.name }
}

Output of gradle -q copy

> gradle -q copy
albatross
shark
tuna

albatross

It is important to note that the returned files of the copied configuration are often but not always the same than the returned files of the dependency subset of the original configuration. In case of version conflicts between dependencies of the subset and dependencies not belonging to the subset the resolve result might be different.

Example 23.24. Configuration.copy vs. Configuration.files

build.gradle

task copyVsFiles << {
    configurations.sealife.copyRecursive { dep -> dep.name == 'orca' }
        .each { file -> println file.name }
    println()
    configurations.sealife.files { dep -> dep.name == 'orca' }
        .each { file -> println file.name }
}

Output of gradle -q copyVsFiles

> gradle -q copyVsFiles
orca-1.0.jar
seal-1.0.jar

orca-1.0.jar
seal-2.0.jar

In the example above, orca has a dependency on seal-1.0 whereas shark has a dependency onseal-2.0. The original configuration has therefore a version conflict which is resolved to the newer seal-2.0 version. The files method therefore returns seal-2.0 as a transitive dependency oforca. The copied configuration only has orca as a dependency and therefore there is no version conflict and seal-1.0 is returned as a transitive dependency.

Once a configuration is resolved it is immutable. Changing its state or the state of one of its dependencies will cause an exception. You can always copy a resolved configuration. The copied configuration is in the unresolved state and can be freshly resolved.

To learn more about the API of the configuration class see the API documentation: Configuration.

23.6. Repositories

Gradle repository management, based on Apache Ivy, gives you a lot of freedom regarding repository layout and retrieval policies. Additionally Gradle provides various convenience method to add pre-configured repositories.

You may configure any number of repositories, each of which is treated independently by Gradle. If Gradle finds a module descriptor in a particular repository, it will attempt to download all of the artifacts for that module from the same repository. Although module meta-data and module artifacts must be located in the same repository, it is possible to compose a single repository of multiple URLs, giving multiple locations to search for meta-data files and jar files.

There are several different types of repositories you can declare:

Table 23.2. Repository types

Type Description
Maven central repository A pre-configured repository that looks for dependencies in Maven Central.
Maven JCenter repository A pre-configured repository that looks for dependencies in Bintray's JCenter.
Maven local repository A pre-configured repository that looks for dependencies in the local Maven repository.
Maven repository A Maven repository. Can be located on the local filesystem or at some remote location.
Ivy repository An Ivy repository. Can be located on the local filesystem or at some remote location.
Flat directory repository A simple repository on the local filesystem. Does not support any meta-data formats.

23.6.1. Maven central repository

To add the central Maven 2 repository (http://repo1.maven.org/maven2) simply add this to your build script:

Example 23.25. Adding central Maven repository

build.gradle

repositories {
    mavenCentral()
}

Now Gradle will look for your dependencies in this repository.

Warning: Be aware that the central Maven 2 repository is HTTP only and HTTPS is not supported. If you need a public HTTPS enabled central repository, you can use the JCenter public repository (see Section 23.6.2, “Maven JCenter repository”).

23.6.2. Maven JCenter repository

Bintray's JCenter is an up-to-date collection of all popular Maven OSS artifacts, including artifacts published directly to Bintray.

To add the JCenter Maven repository (https://jcenter.bintray.com) simply add this to your build script:

Example 23.26. Adding Bintray's JCenter Maven repository

build.gradle

repositories {
    jcenter()
}

Now Gradle will look for your dependencies in the JCenter repository. jcenter() uses HTTPS to connect to the repository. If you want to use HTTP you can configure jcenter():

Example 23.27. Using Bintrays's JCenter with HTTP

build.gradle

repositories {
    jcenter {
        url "http://jcenter.bintray.com/"
    }
}

23.6.3. Local Maven repository

To use the local Maven cache as a repository you can do:

Example 23.28. Adding the local Maven cache as a repository

build.gradle

repositories {
    mavenLocal()
}

Gradle uses the same logic as Maven to identify the location of your local Maven cache. If a local repository location is defined in a settings.xml, this location will be used. The settings.xml in USER_HOME/.m2 takes precedence over the settings.xml in M2_HOME/conf. If no settings.xml is available, Gradle uses the default location USER_HOME/.m2/repository.

23.6.4. Maven repositories

For adding a custom Maven repository you can do:

Example 23.29. Adding custom Maven repository

build.gradle

repositories {
    maven {
        url "http://repo.mycompany.com/maven2"
    }
}

Sometimes a repository will have the POMs published to one location, and the JARs and other artifacts published at another location. To define such a repository, you can do:

Example 23.30. Adding additional Maven repositories for JAR files

build.gradle

repositories {
    maven {
        // Look for POMs and artifacts, such as JARs, here
        url "http://repo2.mycompany.com/maven2"
        // Look for artifacts here if not found at the above location
        artifactUrls "http://repo.mycompany.com/jars"
        artifactUrls "http://repo.mycompany.com/jars2"
    }
}

Gradle will look at the first URL for the POM and the JAR. If the JAR can't be found there, the artifact URLs are used to look for JARs.

23.6.4.1. Accessing password protected Maven repositories

To access a Maven repository which uses basic authentication, you specify the username and password to use when you define the repository:

Example 23.31. Accessing password protected Maven repository

build.gradle

repositories {
    maven {
        credentials {
            username 'user'
            password 'password'
        }
        url "http://repo.mycompany.com/maven2"
    }
}

It is advisable to keep your username and password in gradle.properties rather than directly in the build file.

23.6.5. Flat directory repository

If you want to use a (flat) filesystem directory as a repository, simply type:

Example 23.32. Flat repository resolver

build.gradle

repositories {
    flatDir {
        dirs 'lib'
    }
    flatDir {
        dirs 'lib1', 'lib2'
    }
}

This adds repositories which look into one or more directories for finding dependencies. Note that this type of repository does not support any meta-data formats like Ivy XML or Maven POM files. Instead, Gradle will dynamically generate a module descriptor (without any dependency information) based on the presence of artifacts. However, as Gradle prefers to use modules whose descriptor has been created from real meta-data rather than being generated, flat directory repositories cannot be used to override artifacts with real meta-data from other repositories. So, for example, if Gradle finds only jmxri-1.2.1.jar in a flat directory repository, but jmxri-1.2.1.pom in another repository that supports meta-data, it will use the second repository to provide the module. For the use case of overriding remote artifacts with local ones consider using an Ivy or Maven repository instead whose URL points to a local directory. If you only work with flat directory repositories you don't need to set all attributes of a dependency. See Section 23.4.8, “Optional attributes”.

23.6.6. Ivy repositories

23.6.6.1. Defining an Ivy repository with a standard layout

Example 23.33. Ivy repository

build.gradle

repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
    }
}

23.6.6.2. Defining a named layout for an Ivy repository

You can specify that your repository conforms to the Ivy or Maven default layout by using a named layout.

Example 23.34. Ivy repository with named layout

build.gradle

repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
        layout "maven"
    }
}

Valid named layout values are 'gradle' (the default), 'maven', 'ivy' and 'pattern'. See IvyArtifactRepository.layout(java.lang.String, groovy.lang.Closure) in the API documentation for details of these named layouts.

23.6.6.3. Defining custom pattern layout for an Ivy repository

To define an Ivy repository with a non-standard layout, you can define a 'pattern' layout for the repository:

Example 23.35. Ivy repository with pattern layout

build.gradle

repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
        layout "pattern", {
            artifact "[module]/[revision]/[type]/[artifact].[ext]"
        }
    }
}

To define an Ivy repository which fetches Ivy files and artifacts from different locations, you can define separate patterns to use to locate the Ivy files and artifacts:

Each artifact or ivy specified for a repository adds an additional pattern to use. The patterns are used in the order that they are defined.

Example 23.36. Ivy repository with multiple custom patterns

build.gradle

repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
        layout "pattern", {
            artifact "3rd-party-artifacts/[organisation]/[module]/[revision]/[artifact]-[revision].[ext]"
            artifact "company-artifacts/[organisation]/[module]/[revision]/[artifact]-[revision].[ext]"
            ivy "ivy-files/[organisation]/[module]/[revision]/ivy.xml"
        }
    }
}

Optionally, a repository with pattern layout can have its 'organisation' part laid out in Maven style, with forward slashes replacing dots as separators. For example, the organisation my.company would then be represented as my/company.

Example 23.37. Ivy repository with Maven compatible layout

build.gradle

repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
        layout "pattern", {
            artifact "[organisation]/[module]/[revision]/[artifact]-[revision].[ext]"
            m2compatible = true
        }
    }
}

23.6.6.4. Accessing password protected Ivy repositories

To access an Ivy repository which uses basic authentication, you specify the username and password to use when you define the repository:

Example 23.38. Ivy repository

build.gradle

repositories {
    ivy {
        url 'http://repo.mycompany.com'
        credentials {
            username 'user'
            password 'password'
        }
    }
}

23.6.7. Supported repository transport protocols

Maven and Ivy repositories support the use of various transport protocols. At the moment the following protocols are supported:

Table 23.3. Repository transport protocols

Type Credential types
file none
http username/password
https username/password
sftp username/password
s3 access key/secret key

To define a repository use the repositories configuration block. Within the repositories closure, a Maven repository is declared with maven. An Ivy repository is declared with ivy. The transport protocol is part of the URL definition for a repository. The following build script demonstrates how to create a HTTP-based Maven and Ivy repository:

Example 23.39. Declaring a Maven and Ivy repository

build.gradle

repositories {
    maven {
        url "http://repo.mycompany.com/maven2"
    }

    ivy {
        url "http://repo.mycompany.com/repo"
    }
}

If authentication is required for a repository, the relevant credentials can be provided. The following example shows how to provide username/password-based authentication for SFTP repositories:

Example 23.40. Providing credentials to a Maven and Ivy repository

build.gradle

repositories {
    maven {
        url "sftp://repo.mycompany.com:22/maven2"
        credentials {
            username 'user'
            password 'password'
        }
    }

    ivy {
        url "sftp://repo.mycompany.com:22/repo"
        credentials {
            username 'user'
            password 'password'
        }
    }
}

When using an AWS S3 backed repository you need to authenticate using AwsCredentials, providing access-key and a private-key. The following example shows how to declare a S3 backed repository and providing AWS credentials:

Example 23.41. Declaring a S3 backed Maven and Ivy repository

build.gradle

repositories {
    maven {
        url "s3://myCompanyBucket/maven2"
        credentials(AwsCredentials) {
            accessKey "someKey"
            secretKey "someSecret"
        }
    }

    ivy {
        url "s3://myCompanyBucket/ivyrepo"
        credentials(AwsCredentials) {
            accessKey "someKey"
            secretKey "someSecret"
        }
    }
}

23.6.7.1. S3 configuration properties

The following system properties can be used to configure the interactions with s3 repositories:

Table 23.4. S3 Configuration Properties

Property Description
org.gradle.s3.endpoint Used to override the AWS S3 endpoint when using a non AWS, S3 API compatible, storage service.
org.gradle.s3.maxErrorRetry Specifies the maximum number of times to retry a request in the event that the S3 server responds with a HTTP 5xx status code. When not specified a default value of 3 is used.

23.6.7.2. S3 URL formats

S3 URL's are 'virtual-hosted-style' and must be in the following format s3://<bucketName>[.<regionSpecificEndpoint>]/<s3Key>

e.g. s3://myBucket.s3.eu-central-1.amazonaws.com/maven/release

  • myBucket is the AWS S3 bucket name.
  • s3.eu-central-1.amazonaws.com is the optional region specific endpoint.
  • /maven/release is the AWS S3 key (unique identifier for an object within a bucket)

23.6.7.3. S3 proxy settings

A proxy for S3 can be configured using the following system properties:

  • https.proxyHost
  • https.proxyPort
  • https.proxyUser
  • https.proxyPassword
  • https.nonProxyHosts

If the 'org.gradle.s3.endpoint' property has been specified with a http (not https) URI the following system proxy settings can be used:

  • http.proxyHost
  • http.proxyPort
  • http.proxyUser
  • http.proxyPassword
  • http.nonProxyHosts

23.6.7.4. AWS S3 V4 Signatures (AWS4-HMAC-SHA256)

Some of the AWS S3 regions (eu-central-1 - Frankfurt) require that all HTTP requests are signed in accordance with AWS's signature version 4. It is recommended to specify S3 URL's containing the region specific endpoint when using buckets that require V4 signatures. e.g. s3://somebucket.s3.eu-central-1.amazonaws.com/maven/release

NOTE: When a region-specific endpoint is not specified for buckets requiring V4 Signatures, Gradle will use the default AWS region (us-east-1) and the following warning will appear on the console:

Attempting to re-send the request to .... with AWS V4 authentication. To avoid this warning in the future, please use region-specific endpoint to access buckets located in regions that require V4 signing.

Failing to specify the region-specific endpoint for buckets requiring V4 signatures means:

  • 3 round-trips to AWS, as opposed to one, for every file upload and download.
  • Depending on location - increased network latencies and slower builds.
  • Increased likelihood of transmission failures.

23.6.7.5. Configuring HTTP authentication schemes

When configuring a repository using HTTP or HTTPS transport protocols, multiple authentication schemes are available. By default, Gradle will attempt to use all schemes that are supported by the Apache HttpClient library, documented here. In some cases, it may be preferable to explicitly specify which authentication schemes should be used when exchanging credentials with a remote server. When explicitly declared, only those schemes are used when authenticating to a remote repository. The following example show how to configure a repository to use only digest authentication:

Example 23.42. Configure repository to use only digest authentication

build.gradle

repositories {
    maven {
        url 'https://repo.mycompany.com/maven2'
        credentials {
            username 'user'
            password 'password'
        }
        authentication {
            digest(DigestAuthentication)
        }
    }
}

Currently supported authentication schemes are:

Table 23.5. Authentication schemes

Type Description
BasicAuthentication Basic access authentication over HTTP. When using this scheme, credentials are sent preemptively.
DigestAuthentication Digest access authentication over HTTP.

23.6.7.6. Using preemptive authentication

Gradle's default behavior is to only submit credentials when a server responds with an authentication challenge in the form of a HTTP 401 response. In some cases, the server will respond with a different code (ex. for repositories hosted on GitHub a 404 is returned) causing dependency resolution to fail. To get around this behavior, credentials may be sent to the server preemptively. To enable preemptive authentication simply configure your repository to explicitly use the BasicAuthentication scheme:

Example 23.43. Configure repository to use preemptive authentication

build.gradle

repositories {
    maven {
        url 'https://repo.mycompany.com/maven2'
        credentials {
            username 'user'
            password 'password'
        }
        authentication {
            basic(BasicAuthentication)
        }
    }
}

23.6.8. Working with repositories

To access a repository:

Example 23.44. Accessing a repository

build.gradle

println repositories.localRepository.name
println repositories['localRepository'].name

To configure a repository:

Example 23.45. Configuration of a repository

build.gradle

repositories {
    flatDir {
        name 'localRepository'
    }
}
repositories {
    localRepository {
        dirs 'lib'
    }
}
repositories.localRepository {
    dirs 'lib'
}

23.6.9. More about Ivy resolvers

Gradle is extremely flexible regarding repositories:

  • There are many options for the protocol to communicate with the repository (e.g. filesystem, http, ssh, sftp ...)

  • The protocol sftp currently only supports username/password-based authentication.

  • Each repository can have its own layout.

Let's say, you declare a dependency on the junit:junit:3.8.2 library. Now how does Gradle find it in the repositories? Somehow the dependency information has to be mapped to a path. In contrast to Maven, where this path is fixed, with Gradle you can define a pattern that defines what the path will look like. Here are some examples: [12]

// Maven2 layout (if a repository is marked as Maven2 compatible, the organization (group) is split into subfolders according to the dots.)
someroot/[organisation]/[module]/[revision]/[module]-[revision].[ext]

// Typical layout for an Ivy repository (the organization is not split into subfolder)
someroot/[organisation]/[module]/[revision]/[type]s/[artifact].[ext]

// Simple layout (the organization is not used, no nested folders.)
someroot/[artifact]-[revision].[ext]

To add any kind of repository (you can pretty easy write your own ones) you can do:

Example 23.46. Definition of a custom repository

build.gradle

repositories {
    ivy {
        ivyPattern "$projectDir/repo/[organisation]/[module]-ivy-[revision].xml"
        artifactPattern "$projectDir/repo/[organisation]/[module]-[revision](-[classifier]).[ext]"
    }
}

An overview of which Resolvers are offered by Ivy and thus also by Gradle can be found here. With Gradle you just don't configure them via XML but directly via their API.

23.7. How dependency resolution works

Gradle takes your dependency declarations and repository definitions and attempts to download all of your dependencies by a process called dependency resolution. Below is a brief outline of how this process works.

  • Given a required dependency, Gradle first attempts to resolve the module for that dependency. Each repository is inspected in order, searching first for a module descriptor file (POM or Ivy file) that indicates the presence of that module. If no module descriptor is found, Gradle will search for the presence of the primary module artifact file indicating that the module exists in the repository.

    • If the dependency is declared as a dynamic version (like 1.+), Gradle will resolve this to the newest available static version (like 1.2) in the repository. For Maven repositories, this is done using the maven-metadata.xml file, while for Ivy repositories this is done by directory listing.

    • If the module descriptor is a POM file that has a parent POM declared, Gradle will recursively attempt to resolve each of the parent modules for the POM.

  • Once each repository has been inspected for the module, Gradle will choose the 'best' one to use. This is done using the following criteria:

    • For a dynamic version, a 'higher' static version is preferred over a 'lower' version.
    • Modules declared by a module descriptor file (Ivy or POM file) are preferred over modules that have an artifact file only.
    • Modules from earlier repositories are preferred over modules in later repositories.

    When the dependency is declared by a static version and a module descriptor file is found in a repository, there is no need to continue searching later repositories and the remainder of the process is short-circuited.

  • All of the artifacts for the module are then requested from the same repository that was chosen in the process above.

23.8. Fine-tuning the dependency resolution process

In most cases, Gradle's default dependency management will resolve the dependencies that you want in your build. In some cases, however, it can be necessary to tweak dependency resolution to ensure that your build receives exactly the right dependencies.

There are a number of ways that you can influence how Gradle resolves dependencies.

23.8.1. Forcing a particular module version

Forcing a module version tells Gradle to always use a specific version for given dependency (transitive or not), overriding any version specified in a published module descriptor. This can be very useful when tackling version conflicts - for more information see Section 23.2.3, “Resolve version conflicts”.

Force versions can also be used to deal with rogue metadata of transitive dependencies. If a transitive dependency has poor quality metadata that leads to problems at dependency resolution time, you can force Gradle to use a newer, fixed version of this dependency. For an example, see the ResolutionStrategy class in the API documentation. Note that 'dependency resolve rules' (outlined below) provide a more powerful mechanism for replacing a broken module dependency. See Section 23.8.2.3, “Blacklisting a particular version with a replacement”.

23.8.2. Using dependency resolve rules

A dependency resolve rule is executed for each resolved dependency, and offers a powerful api for manipulating a requested dependency prior to that dependency being resolved. This feature is incubating, but currently offers the ability to change the group, name and/or version of a requested dependency, allowing a dependency to be substituted with a completely different module during resolution.

Dependency resolve rules provide a very powerful way to control the dependency resolution process, and can be used to implement all sorts of advanced patterns in dependency management. Some of these patterns are outlined below. For more information and code samples see the ResolutionStrategy class in the API documentation.

23.8.2.1. Modelling releaseable units

Often an organisation publishes a set of libraries with a single version; where the libraries are built, tested and published together. These libraries form a 'releasable unit', designed and intended to be used as a whole. It does not make sense to use libraries from different releasable units together.

But it is easy for transitive dependency resolution to violate this contract. For example:

  • module-a depends on releasable-unit:part-one:1.0
  • module-b depends on releasable-unit:part-two:1.1

A build depending on both module-a and module-b will obtain different versions of libraries within the releasable unit.

Dependency resolve rules give you the power to enforce releasable units in your build. Imagine a releasable unit defined by all libraries that have 'org.gradle' group. We can force all of these libraries to use a consistent version:

Example 23.47. Forcing consistent version for a group of libraries

build.gradle

configurations.all {
    resolutionStrategy.eachDependency { DependencyResolveDetails details ->
        if (details.requested.group == 'org.gradle') {
            details.useVersion '1.4'
        }
    }
}


23.8.2.2. Implement a custom versioning scheme

In some corporate environments, the list of module versions that can be declared in Gradle builds is maintained and audited externally. Dependency resolve rules provide a neat implementation of this pattern:

  • In the build script, the developer declares dependencies with the module group and name, but uses a placeholder version, for example: 'default'.
  • The 'default' version is resolved to a specific version via a dependency resolve rule, which looks up the version in a corporate catalog of approved modules.

This rule implementation can be neatly encapsulated in a corporate plugin, and shared across all builds within the organisation.

Example 23.48. Using a custom versioning scheme

build.gradle

configurations.all {
    resolutionStrategy.eachDependency { DependencyResolveDetails details ->
        if (details.requested.version == 'default') {
            def version = findDefaultVersionInCatalog(details.requested.group, details.requested.name)
            details.useVersion version
        }
    }
}

def findDefaultVersionInCatalog(String group, String name) {
    //some custom logic that resolves the default version into a specific version
    "1.0"
}


23.8.2.3. Blacklisting a particular version with a replacement

Dependency resolve rules provide a mechanism for blacklisting a particular version of a dependency and providing a replacement version. This can be useful if a certain dependency version is broken and should not be used, where a dependency resolve rule causes this version to be replaced with a known good version. One example of a broken module is one that declares a dependency on a library that cannot be found in any of the public repositories, but there are many other reasons why a particular module version is unwanted and a different version is preferred.

In example below, imagine that version 1.2.1 contains important fixes and should always be used in preference to 1.2. The rule provided will enforce just this: any time version 1.2 is encountered it will be replaced with 1.2.1. Note that this is different from a forced version as described above, in that any other versions of this module would not be affected. This means that the 'newest' conflict resolution strategy would still select version 1.3 if this version was also pulled transitively.

Example 23.49. Blacklisting a version with a replacement

build.gradle

configurations.all {
    resolutionStrategy.eachDependency { DependencyResolveDetails details ->
        if (details.requested.group == 'org.software' && details.requested.name == 'some-library' && details.requested.version == '1.2') {
            //prefer different version which contains some necessary fixes
            details.useVersion '1.2.1'
        }
    }
}


23.8.2.4. Substituting a dependency module with a compatible replacement

At times a completely different module can serve as a replacement for a requested module dependency. Examples include using 'groovy' in place of 'groovy-all', or using 'log4j-over-slf4j' instead of 'log4j'. Starting with Gradle 1.5 you can make these substitutions using dependency resolve rules:

Example 23.50. Changing dependency group and/or name at the resolution

build.gradle

configurations.all {
    resolutionStrategy.eachDependency { DependencyResolveDetails details ->
        if (details.requested.name == 'groovy-all') {
            //prefer 'groovy' over 'groovy-all':
            details.useTarget group: details.requested.group, name: 'groovy', version: details.requested.version
        }
        if (details.requested.name == 'log4j') {
            //prefer 'log4j-over-slf4j' over 'log4j', with fixed version:
            details.useTarget "org.slf4j:log4j-over-slf4j:1.7.10"
        }
    }
}


23.8.3. Dependency Substitution Rules

Dependency substitution rules work similarly to dependency resolve rules. In fact, many capabilities of dependency resolve rules can be implemented with dependency substitution rules. They allow project and module dependencies to be transparently substituted with specified replacements. Unlike dependency resolve rules, dependency substitution rules allow project and module dependencies to be substituted interchangeably.

NOTE: Adding a dependency substitution rule to a configuration changes the timing of when that configuration is resolved. Instead of being resolved on first use, the configuration is instead resolved when the task graph is being constructed. This can have unexpected consequences if the configuration is being further modified during task execution, or if the configuration relies on modules that are published during execution of another task.

To explain:

  • A Configuration can be declared as an input to any Task, and that configuration can include project dependencies when it is resolved.
  • If a project dependency is an input to a Task (via a configuration), then tasks to built the project artifacts must be added to the task dependencies.
  • In order to determine the project dependencies that are inputs to a task, Gradle needs to resolve the Configuration inputs.
  • Because the Gradle task graph is fixed once task execution has commenced, Gradle needs to perform this resolution prior to executing any tasks.

In the absence of dependency substitution rules, Gradle knows that an external module dependency will never transitively reference a project dependency. This makes it easy to determine the full set of project dependencies for a configuration through simple graph traversal. With this functionality, Gradle can no longer make this assumption, and must perform a full resolve in order to determine the project dependencies.

23.8.3.1. Substituting an external module dependency with a project dependency

One use case for dependency substitution is to use a locally developed version of a module in place of one that is downloaded from an external repository. This could be useful for testing a local, patched version of a dependency.

The module to be replaced can be declared with or without a version specified.

Example 23.51. Substituting a module with a project

build.gradle

configurations.all {
    resolutionStrategy.dependencySubstitution {
        substitute module("org.utils:api") with project(":api")
        substitute module("org.utils:util:2.5") with project(":util")
    }
}

Note that a project that is substituted must be included in the multi-project build (via settings.gradle). Dependency substitution rules take care of replacing the module dependency with the project dependency and wiring up any task dependencies, but do not implicitly include the project in the build.

23.8.3.2. Substituting a project dependency with a module replacement

Another way to use substitution rules is to replace a project dependency with a module in a multi-project build. This can be useful to speed up development with a large multi-project build, by allowing a subset of the project dependencies to be downloaded from a repository rather than being built.

The module to be used as a replacement must be declared with a version specified.

Example 23.52. Substituting a project with a module

build.gradle

configurations.all {
    resolutionStrategy.dependencySubstitution {
        substitute project(":api") with module("org.utils:api:1.3")
    }
}

When a project dependency has been replaced with a module dependency, that project is still included in the overall multi-project build. However, tasks to build the replaced dependency will not be executed in order to build the resolve the depending Configuration.

23.8.3.3. Conditionally substituting a dependency

A common use case for dependency substitution is to allow more flexible assembly of sub-projects within a multi-project build. This can be useful for developing a local, patched version of an external dependency or for building a subset of the modules within a large multi-project build.

The following example uses a dependency substitution rule to replace any module dependency with the group "org.example", but only if a local project matching the dependency name can be located.

Example 23.53. Conditionally substituting a dependency

build.gradle

configurations.all {
    resolutionStrategy.dependencySubstitution.all { DependencySubstitution dependency ->
        if (dependency.requested instanceof ModuleComponentSelector && dependency.requested.group == "org.example") {
            def targetProject = findProject(":${dependency.requested.module}")
            if (targetProject != null) {
                dependency.useTarget targetProject
            }
        }
    }
}

Note that a project that is substituted must be included in the multi-project build (via settings.gradle). Dependency substitution rules take care of replacing the module dependency with the project dependency, but do not implicitly include the project in the build.

23.8.4. Specifying default dependencies for a configuration

A configuration can be configured with default dependencies to be used if no dependencies are explicitly set for the configuration. A primary use case of this functionality is for developing plugins that make use of versioned tools that the user might override. By specifying default dependencies, the plugin can use a default version of the tool only if the user has not specified a particular version to use.

Example 23.54. Specifying default dependencies on a configuration

build.gradle

configurations {
    pluginTool {
        defaultDependencies { dependencies ->
            dependencies.add(this.project.dependencies.create("org.gradle:my-util:1.0"))
        }
    }
}

23.8.5. Enabling Ivy dynamic resolve mode

Gradle's Ivy repository implementations support the equivalent to Ivy's dynamic resolve mode. Normally, Gradle will use the rev attribute for each dependency definition included in an ivy.xml file. In dynamic resolve mode, Gradle will instead prefer the revConstraint attribute over the rev attribute for a given dependency definition. If the revConstraint attribute is not present, the rev attribute is used instead.

To enable dynamic resolve mode, you need to set the appropriate option on the repository definition. A couple of examples are shown below. Note that dynamic resolve mode is only available for Gradle's Ivy repositories. It is not available for Maven repositories, or custom Ivy DependencyResolver implementations.

Example 23.55. Enabling dynamic resolve mode

build.gradle

// Can enable dynamic resolve mode when you define the repository
repositories {
    ivy {
        url "http://repo.mycompany.com/repo"
        resolve.dynamicMode = true
    }
}

// Can use a rule instead to enable (or disable) dynamic resolve mode for all repositories
repositories.withType(IvyArtifactRepository) {
    resolve.dynamicMode = true
}

23.8.6. Component metadata rules

Each module (also called component) has metadata associated with it, such as its group, name, version, dependencies, and so on. This metadata typically originates in the module's descriptor. Metadata rules allow certain parts of a module's metadata to be manipulated from within the build script. They take effect after a module's descriptor has been downloaded, but before it has been selected among all candidate versions. This makes metadata rules another instrument for customizing dependency resolution.

One piece of module metadata that Gradle understands is a module's status scheme. This concept, also known from Ivy, models the different levels of maturity that a module transitions through over time. The default status scheme, ordered from least to most mature status, is integration, milestone, release. Apart from a status scheme, a module also has a (current) status, which must be one of the values in its status scheme. If not specified in the (Ivy) descriptor, the status defaults to integration for Ivy modules and Maven snapshot modules, and release for Maven modules that aren't snapshots.

A module's status and status scheme are taken into consideration when a latest version selector is resolved. Specifically, latest.someStatus will resolve to the highest module version that has status someStatus or a more mature status. For example, with the default status scheme in place, latest.integration will select the highest module version regardless of its status (because integration is the least mature status), whereas latest.release will select the highest module version with status release. Here is what this looks like in code:

Example 23.56. 'Latest' version selector

build.gradle

dependencies {
    config1 "org.sample:client:latest.integration"
    config2 "org.sample:client:latest.release"
}

task listConfigs << {
    configurations.config1.each { println it.name }
    println()
    configurations.config2.each { println it.name}
}

Output of gradle -q listConfigs

> gradle -q listConfigs
client-1.5.jar

client-1.4.jar

The next example demonstrates latest selectors based on a custom status scheme declared in a component metadata rule that applies to all modules:

Example 23.57. Custom status scheme

build.gradle

dependencies {
    config3 "org.sample:api:latest.silver"
    components {
        all { ComponentMetadataDetails details ->
            if (details.id.group == "org.sample" && details.id.name == "api") {
                details.statusScheme = ["bronze", "silver", "gold", "platinum"]
            }
        }
    }
}

Component metadata rules can be applied to a specified module. Modules must be specified in the form of "group:module".

Example 23.58. Custom status scheme by module

build.gradle

dependencies {
    config4 "org.sample:lib:latest.prod"
    components {
        withModule('org.sample:lib') { ComponentMetadataDetails details ->
            details.statusScheme = ["int", "rc", "prod"]
        }
    }
}

Gradle can also create component metadata rules utilizing Ivy-specific metadata for modules resolved from an Ivy repository. Values from the Ivy descriptor are made available via the IvyModuleDescriptor interface.

Example 23.59. Ivy component metadata rule

build.gradle

dependencies {
    config6 "org.sample:lib:latest.rc"
    components {
        withModule("org.sample:lib") { ComponentMetadataDetails details, IvyModuleDescriptor ivyModule ->
            if (ivyModule.branch == 'testing') {
                details.status = "rc"
            }
        }
    }
}

Note that any rule that declares specific arguments must always include a ComponentMetadataDetails argument as the first argument. The second Ivy metadata argument is optional.

Component metadata rules can also be defined using a rule source object. A rule source object is any object that contains exactly one method that defines the rule action and is annotated with @Mutate.

This method:

Example 23.60. Rule source component metadata rule

build.gradle

dependencies {
    config5 "org.sample:api:latest.gold"
    components {
        withModule('org.sample:api', new CustomStatusRule())
    }
}

class CustomStatusRule {
    @Mutate
    void setStatusScheme(ComponentMetadataDetails details) {
        details.statusScheme = ["bronze", "silver", "gold", "platinum"]
    }
}

23.8.7. Component Selection Rules

Component selection rules may influence which component instance should be selected when multiple versions are available that match a version selector. Rules are applied against every available version and allow the version to be explicitly rejected by rule. This allows Gradle to ignore any component instance that does not satisfy conditions set by the rule. Examples include:

  • For a dynamic version like '1.+' certain versions may be explicitly rejected from selection
  • For a static version like '1.4' an instance may be rejected based on extra component metadata such as the Ivy branch attribute, allowing an instance from a subsequent repository to be used.

Rules are configured via the ComponentSelectionRules object. Each rule configured will be called with a ComponentSelection object as an argument which contains information about the candidate version being considered. Calling ComponentSelection.reject(java.lang.String) causes the given candidate version to be explicitly rejected, in which case the candidate will not be considered for the selector.

The following example shows a rule that disallows a particular version of a module but allows the dynamic version to choose the next best candidate.

Example 23.61. Component selection rule

build.gradle

configurations {
    rejectConfig {
        resolutionStrategy {
            componentSelection {
                // Accept the highest version matching the requested version that isn't '1.5'
                all { ComponentSelection selection ->
                    if (selection.candidate.group == 'org.sample' && selection.candidate.module == 'api' && selection.candidate.version == '1.5') {
                        selection.reject("version 1.5 is broken for 'org.sample:api'")
                    }
                }
            }
        }
    }
}

dependencies {
    rejectConfig "org.sample:api:1.+"
}

Note that version selection is applied starting with the highest version first. The version selected will be the first version found that all component selection rules accept. A version is considered accepted no rule explicitly rejects it.

Similarly, rules can be targeted at specific modules. Modules must be specified in the form of "group:module".

Example 23.62. Component selection rule with module target

build.gradle

configurations {
    targetConfig {
        resolutionStrategy {
            componentSelection {
                withModule("org.sample:api") { ComponentSelection selection ->
                    if (selection.candidate.version == "1.5") {
                        selection.reject("version 1.5 is broken for 'org.sample:api'")
                    }
                }
            }
        }
    }
}

Component selection rules can also consider component metadata when selecting a version. Possible metadata arguments that can be considered are ComponentMetadata and IvyModuleDescriptor.

Example 23.63. Component selection rule with metadata

build.gradle

configurations {
    metadataRulesConfig {
        resolutionStrategy {
            componentSelection {
                // Reject any versions with a status of 'experimental'
                all { ComponentSelection selection, ComponentMetadata metadata ->
                    if (selection.candidate.group == 'org.sample' && metadata.status == 'experimental') {
                        selection.reject("don't use experimental candidates from 'org.sample'")
                    }
                }
                // Accept the highest version with either a "release" branch or a status of 'milestone'
                withModule('org.sample:api') { ComponentSelection selection, IvyModuleDescriptor descriptor, ComponentMetadata metadata ->
                    if (descriptor.branch != "release" && metadata.status != 'milestone') {
                        selection.reject("'org.sample:api' must have testing branch or milestone status")
                    }
                }
            }
        }
    }
}

Note that a ComponentSelection argument is always required as the first parameter when declaring a component selection rule with additional Ivy metadata parameters, but the metadata parameters can be declared in any order.

Lastly, component selection rules can also be defined using a rule source object. A rule source object is any object that contains exactly one method that defines the rule action and is annotated with @Mutate.

This method:

Example 23.64. Component selection rule using a rule source object

build.gradle

class RejectTestBranch {
    @Mutate
    void evaluateRule(ComponentSelection selection, IvyModuleDescriptor ivy) {
        if (ivy.branch == "test") {
            selection.reject("reject test branch")
        }
    }
}

configurations {
    ruleSourceConfig {
        resolutionStrategy {
            componentSelection {
                all new RejectTestBranch()
            }
        }
    }
}

23.8.8. Module replacement rules

Module replacement rules allow a build to declare that a legacy library has been replaced by a new one. A good example when a new library replaced a legacy one is the "google-collections" -> "guava" migration. The team that created google-collections decided to change the module name from "com.google.collections:google-collections" into "com.google.guava:guava". This a legal scenario in the industry: teams need to be able to change the names of products they maintain, including the module coordinates. Renaming of the module coordinates has impact on conflict resolution.

To explain the impact on conflict resolution, let's consider the "google-collections" -> "guava" scenario. It may happen that both libraries are pulled into the same dependency graph. For example, "our" project depends on guava but some of our dependencies pull in a legacy version of google-collections. This can cause runtime errors, for example during test or application execution. Gradle does not automatically resolve the google-collections VS guava conflict because it is not considered as a "version conflict". It's because the module coordinates for both libraries are completely different and conflict resolution is activated when "group" and "name" coordinates are the same but there are different versions available in the dependency graph (for more info, please refer to the section on conflict resolution). Traditional remedies to this problem are:

  • Declare exclusion rule to avoid pulling in "google-collections" to graph. It is probably the most popular approach.
  • Avoid dependencies that pull in legacy libraries.
  • Upgrade the dependency version if the new version no longer pulls in a legacy library.
  • Downgrade to "google-collections". It's not recommended, just mentioned for completeness.

Traditional approaches work but they are not general enough. For example, an organisation wants to resolve the google-collections VS guava conflict resolution problem in all projects. Starting from Gradle 2.2 it is possible to declare that certain module was replaced by other. This enables organisations to include the information about module replacement in the corporate plugin suite and resolve the problem holistically for all Gradle-powered projects in the enterprise.

Example 23.65. Declaring module replacement

build.gradle

dependencies {
    modules {
        module("com.google.collections:google-collections") {
            replacedBy("com.google.guava:guava")
        }
    }
}


For more examples and detailed API, please refer to the DSL reference for ComponentMetadataHandler.

What happens when we declare that "google-collections" are replaced by "guava"? Gradle can use this information for conflict resolution. Gradle will consider every version of "guava" newer/better than any version of "google-collections". Also, Gradle will ensure that only guava jar is present in the classpath / resolved file list. Please note that if only "google-collections" appears in the dependency graph (e.g. no "guava") Gradle will not eagerly replace it with "guava". Module replacement is an information that Gradle uses for resolving conflicts. If there is no conflict (e.g. only "google-collections" or only "guava" in the graph) the replacement information is not used.

Currently it is not possible to declare that certain modules is replaced by a set of modules. However, it is possible to declare that multiple modules are replaced by a single module.

23.9. The dependency cache

Gradle contains a highly sophisticated dependency caching mechanism, which seeks to minimise the number of remote requests made in dependency resolution, while striving to guarantee that the results of dependency resolution are correct and reproducible.

The Gradle dependency cache consists of 2 key types of storage:

  • A file-based store of downloaded artifacts, including binaries like jars as well as raw downloaded meta-data like POM files and Ivy files. The storage path for a downloaded artifact includes the SHA1 checksum, meaning that 2 artifacts with the same name but different content can easily be cached.

  • A binary store of resolved module meta-data, including the results of resolving dynamic versions, module descriptors, and artifacts.

Separating the storage of downloaded artifacts from the cache metadata permits us to do some very powerful things with our cache that would be difficult with a transparent, file-only cache layout.

The Gradle cache does not allow the local cache to hide problems and create other mysterious and difficult to debug behavior that has been a challenge with many build tools. This new behavior is implemented in a bandwidth and storage efficient way. In doing so, Gradle enables reliable and reproducible enterprise builds.

23.9.1. Key features of the Gradle dependency cache

23.9.1.1. Separate metadata cache

Gradle keeps a record of various aspects of dependency resolution in binary format in the metadata cache. The information stored in the metadata cache includes:

  • The result of resolving a dynamic version (e.g. 1.+) to a concrete version (e.g. 1.2).
  • The resolved module metadata for a particular module, including module artifacts and module dependencies.
  • The resolved artifact metadata for a particular artifact, including a pointer to the downloaded artifact file.
  • The absence of a particular module or artifact in a particular repository, eliminating repeated attempts to access a resource that does not exist.

Every entry in the metadata cache includes a record of the repository that provided the information as well as a timestamp that can be used for cache expiry.

23.9.1.2. Repository caches are independent

As described above, for each repository there is a separate metadata cache. A repository is identified by its URL, type and layout. If a module or artifact has not been previously resolved from this repository, Gradle will attempt to resolve the module against the repository. This will always involve a remote lookup on the repository, however in many cases no download will be required (seeSection 23.9.1.3, “Artifact reuse”, below).

Dependency resolution will fail if the required artifacts are not available in any repository specified by the build, even if the local cache has a copy of this artifact which was retrieved from a different repository. Repository independence allows builds to be isolated from each other in an advanced way that no build tool has done before. This is a key feature to create builds that are reliable and reproducible in any environment.

23.9.1.3. Artifact reuse

Before downloading an artifact, Gradle tries to determine the checksum of the required artifact by downloading the sha file associated with that artifact. If the checksum can be retrieved, an artifact is not downloaded if an artifact already exists with the same id and checksum. If the checksum cannot be retrieved from the remote server, the artifact will be downloaded (and ignored if it matches an existing artifact).

As well as considering artifacts downloaded from a different repository, Gradle will also attempt to reuse artifacts found in the local Maven Repository. If a candidate artifact has been downloaded by Maven, Gradle will use this artifact if it can be verified to match the checksum declared by the remote server.

23.9.1.4. Checksum based storage

It is possible for different repositories to provide a different binary artifact in response to the same artifact identifier. This is often the case with Maven SNAPSHOT artifacts, but can also be true for any artifact which is republished without changing it's identifier. By caching artifacts based on their SHA1 checksum, Gradle is able to maintain multiple versions of the same artifact. This means that when resolving against one repository Gradle will never overwrite the cached artifact file from a different repository. This is done without requiring a separate artifact file store per repository.

23.9.1.5. Cache Locking

The Gradle dependency cache uses file-based locking to ensure that it can safely be used by multiple Gradle processes concurrently. The lock is held whenever the binary meta-data store is being read or written, but is released for slow operations such as downloading remote artifacts.

23.9.2. Command line options to override caching

23.9.2.1. Offline

The --offline command line switch tells Gradle to always use dependency modules from the cache, regardless if they are due to be checked again. When running with offline, Gradle will never attempt to access the network to perform dependency resolution. If required modules are not present in the dependency cache, build execution will fail.

23.9.2.2. Refresh

At times, the Gradle Dependency Cache can be out of sync with the actual state of the configured repositories. Perhaps a repository was initially misconfigured, or perhaps a “non-changing” module was published incorrectly. To refresh all dependencies in the dependency cache, use the --refresh-dependencies option on the command line.

The --refresh-dependencies option tells Gradle to ignore all cached entries for resolved modules and artifacts. A fresh resolve will be performed against all configured repositories, with dynamic versions recalculated, modules refreshed, and artifacts downloaded. However, where possible Gradle will check if the previously downloaded artifacts are valid before downloading again. This is done by comparing published SHA1 values in the repository with the SHA1 values for existing downloaded artifacts.

23.9.3. Fine-tuned control over dependency caching

You can fine-tune certain aspects of caching using the ResolutionStrategy for a configuration.

By default, Gradle caches dynamic versions for 24 hours. To change how long Gradle will cache the resolved version for a dynamic version, use:

Example 23.66. Dynamic version cache control

build.gradle

configurations.all {
    resolutionStrategy.cacheDynamicVersionsFor 10, 'minutes'
}

By default, Gradle caches changing modules for 24 hours. To change how long Gradle will cache the meta-data and artifacts for a changing module, use:

Example 23.67. Changing module cache control

build.gradle

configurations.all {
    resolutionStrategy.cacheChangingModulesFor 4, 'hours'
}

For more details, take a look at the API documentation for ResolutionStrategy.

23.10. Strategies for transitive dependency management

Many projects rely on the Maven Central repository. This is not without problems.

  • The Maven Central repository can be down or can be slow to respond.

  • The POM files of many popular projects specify dependencies or other configuration that are just plain wrong (for instance, the POM file of the “commons-httpclient-3.0” module declares JUnit as a runtime dependency).

  • For many projects there is not one right set of dependencies (as more or less imposed by the POM format).

If your project relies on the Maven Central repository you are likely to need an additional custom repository, because:

  • You might need dependencies that are not uploaded to Maven Central yet.

  • You want to deal properly with invalid metadata in a Maven Central POM file.

  • You don't want to expose people to the downtimes or slow response of Maven Central, if they just want to build your project.

It is not a big deal to set-up a custom repository, [13] but it can be tedious to keep it up to date. For a new version, you always have to create the new XML descriptor and the directories. Your custom repository is another infrastructure element which might have downtimes and needs to be updated. To enable historical builds, you need to keep all the past libraries, not to mention a backup of these. It is another layer of indirection. Another source of information you have to lookup. All this is not really a big deal but in its sum it has an impact. Repository managers like Artifactory or Nexus make this easier, but most open source projects don't usually have a host for those products. This is changing with new services like Bintray that let developers host and distribute their release binaries using a self-service repository platform. Bintray also supports sharing approved artifacts though the JCenter public repository to provide a single resolution address for all popular OSS Java artifacts (see Section 23.6.2, “Maven JCenter repository”).

This is a common reason why many projects prefer to store their libraries in their version control system. This approach is fully supported by Gradle. The libraries can be stored in a flat directory without any XML module descriptor files. Yet Gradle offers complete transitive dependency management. You can use either client module dependencies to express the dependency relations, or artifact dependencies in case a first level dependency has no transitive dependencies. People can check out such a project from your source code control system and have everything necessary to build it.

If you are working with a distributed version control system like Git you probably don't want to use the version control system to store libraries as people check out the whole history. But even here the flexibility of Gradle can make your life easier. For example, you can use a shared flat directory without XML descriptors and yet you can have full transitive dependency management, as described above.

You could also have a mixed strategy. If your main concern is bad metadata in the POM file and maintaining custom XML descriptors, then Client Modules offer an alternative. However, you can still use a Maven2 repo or your custom repository as a repository for jars only and still enjoy transitive dependency management. Or you can only provide client modules for POMs with bad metadata. For the jars and the correct POMs you still use the remote repository.

23.10.1. Implicit transitive dependencies

There is another way to deal with transitive dependencies without XML descriptor files. You can do this with Gradle, but we don't recommend it. We mention it for the sake of completeness and comparison with other build tools.

The trick is to use only artifact dependencies and group them in lists. This will directly express your first level dependencies and your transitive dependencies (see Section 23.4.8, “Optional attributes”). The problem with this is that Gradle dependency management will see this as specifying all dependencies as first level dependencies. The dependency reports won't show your real dependency graph and the compile task uses all dependencies, not just the first level dependencies. All in all, your build is less maintainable and reliable than it could be when using client modules, and you don't gain anything.



[10] Gradle supports partial multiproject builds (see Chapter 24, Multi-project Builds).

[12] At http://ant.apache.org/ivy/history/latest-milestone/concept.html you can learn more about ivy patterns.

[13] If you want to shield your project from the downtimes of Maven Central things get more complicated. You probably want to set-up a repository proxy for this. In an enterprise environment this is rather common. For an open source project it looks like overkill.

Chapter 24. Multi-project Builds

The powerful support for multi-project builds is one of Gradle's unique selling points. This topic is also the most intellectually challenging.

A multi-project build in gradle consists of one root project, and one or more subprojects that may also have subprojects.

24.1. Cross project configuration

While each subproject could configure itself in complete isolation of the other subprojects, it is common that subprojects share common traits. It is then usually preferable to share configurations among projects, so the same configuration affects several subprojects.

Let's start with a very simple multi-project build. Gradle is a general purpose build tool at its core, so the projects don't have to be Java projects. Our first examples are about marine life.

24.1.1. Configuration and execution

Section 20.1, “Build phases” describes the phases of every Gradle build. Let's zoom into the configuration and execution phases of a multi-project build. Configuration here means executing the build.gradle file of a project, which implies e.g. downloading all plugins that were declared using 'apply plugin'. By default, the configuration of all projects happens before any task is executed. This means that when a single task, from a single project is requested, all projects of multi-project build are configured first. The reason every project needs to be configured is to support the flexibility of accessing and changing any part of the Gradle project model.

24.1.1.1. Configuration on demand

The Configuration injection feature and access to the complete project model are possible because every project is configured before the execution phase. Yet, this approach may not be the most efficient in a very large multi-project build. There are Gradle builds with a hierarchy of hundreds of subprojects. The configuration time of huge multi-project builds may become noticeable. Scalability is an important requirement for Gradle. Hence, starting from version 1.4 a new incubating 'configuration on demand' mode is introduced.

Configuration on demand mode attempts to configure only projects that are relevant for requested tasks, i.e. it only executes the build.gradle file of projects that are participating in the build. This way, the configuration time of a large multi-project build can be reduced. In the long term, this mode will become the default mode, possibly the only mode for Gradle build execution. The configuration on demand feature is incubating so not every build is guaranteed to work correctly. The feature should work very well for multi-project builds that have decoupled projects (Section 24.9, “Decoupled Projects”). In “configuration on demand” mode, projects are configured as follows:

  • The root project is always configured. This way the typical common configuration is supported (allprojects or subprojects script blocks).
  • The project in the directory where the build is executed is also configured, but only when Gradle is executed without any tasks. This way the default tasks behave correctly when projects are configured on demand.
  • The standard project dependencies are supported and makes relevant projects configured. If project A has a compile dependency on project B then building A causes configuration of both projects.
  • The task dependencies declared via task path are supported and cause relevant projects to be configured. Example: someTask.dependsOn(":someOtherProject:someOtherTask")
  • A task requested via task path from the command line (or Tooling API) causes the relevant project to be configured. For example, building 'projectA:projectB:someTask' causes configuration of projectB.

Eager to try out this new feature? To configure on demand with every build run see Section 11.1, “Configuring the build environment via gradle.properties”. To configure on demand just for a given build please see Appendix D, Gradle Command Line.

24.1.2. Defining common behavior

Let's look at some examples with the following project tree. This is a multi-project build with a root project named water and a subproject named bluewhale.

Example 24.1. Multi-project tree - water & bluewhale projects

Build layout

water/
  build.gradle
  settings.gradle
  bluewhale/

Note: The code for this example can be found at samples/userguide/multiproject/firstExample/water in the ‘-all’ distribution of Gradle.

settings.gradle

include 'bluewhale'

And where is the build script for the bluewhale project? In Gradle build scripts are optional. Obviously for a single project build, a project without a build script doesn't make much sense. For multiproject builds the situation is different. Let's look at the build script for the water project and execute it:

Example 24.2. Build script of water (parent) project

build.gradle

Closure cl = { task -> println "I'm $task.project.name" }
task hello << cl
project(':bluewhale') {
    task hello << cl
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale

Gradle allows you to access any project of the multi-project build from any build script. The Project API provides a method called project(), which takes a path as an argument and returns the Project object for this path. The capability to configure a project build from any build script we call cross project configuration. Gradle implements this via configuration injection.

We are not that happy with the build script of the water project. It is inconvenient to add the task explicitly for every project. We can do better. Let's first add another project called krill to our multi-project build.

Example 24.3. Multi-project tree - water, bluewhale & krill projects

Build layout

water/
  build.gradle
  settings.gradle
  bluewhale/
  krill/

Note: The code for this example can be found at samples/userguide/multiproject/addKrill/water in the ‘-all’ distribution of Gradle.

settings.gradle

include 'bluewhale', 'krill'

Now we rewrite the water build script and boil it down to a single line.

Example 24.4. Water project build script

build.gradle

allprojects {
    task hello << { task -> println "I'm $task.project.name" }
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale
I'm krill

Is this cool or is this cool? And how does this work? The Project API provides a property allprojects which returns a list with the current project and all its subprojects underneath it. If you call allprojects with a closure, the statements of the closure are delegated to the projects associated with allprojects. You could also do an iteration via allprojects.each, but that would be more verbose.

Other build systems use inheritance as the primary means for defining common behavior. We also offer inheritance for projects as you will see later. But Gradle uses configuration injection as the usual way of defining common behavior. We think it provides a very powerful and flexible way of configuring multiproject builds.

Another possibilty for sharing configuration is to use a common external script. See Section 41.3, “Configuring the project using an external build script” for more information.

24.2. Subproject configuration

The Project API also provides a property for accessing the subprojects only.

24.2.1. Defining common behavior

Example 24.5. Defining common behavior of all projects and subprojects

build.gradle

allprojects {
    task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
    hello << {println "- I depend on water"}
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
I'm krill
- I depend on water

You may notice that there are two code snippets referencing the “hello” task. The first one, which uses the “task” keyword, constructs the task and provides it's base configuration. The second piece doesn't use the “task” keyword, as it is further configuring the existing “hello” task. You may only construct a task once in a project, but you may add any number of code blocks providing additional configuration.

24.2.2. Adding specific behavior

You can add specific behavior on top of the common behavior. Usually we put the project specific behavior in the build script of the project where we want to apply this specific behavior. But as we have already seen, we don't have to do it this way. We could add project specific behavior for the bluewhale project like this:

Example 24.6. Defining specific behaviour for particular project

build.gradle

allprojects {
    task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
    hello << {println "- I depend on water"}
}
project(':bluewhale').hello << {
    println "- I'm the largest animal that has ever lived on this planet."
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
I'm krill
- I depend on water

As we have said, we usually prefer to put project specific behavior into the build script of this project. Let's refactor and also add some project specific behavior to the krill project.

Example 24.7. Defining specific behaviour for project krill

Build layout

water/
  build.gradle
  settings.gradle
  bluewhale/
    build.gradle
  krill/
    build.gradle

Note: The code for this example can be found at samples/userguide/multiproject/spreadSpecifics/water in the ‘-all’ distribution of Gradle.

settings.gradle

include 'bluewhale', 'krill'

bluewhale/build.gradle

hello.doLast {
  println "- I'm the largest animal that has ever lived on this planet."
}

krill/build.gradle

hello.doLast {
  println "- The weight of my species in summer is twice as heavy as all human beings."
}

build.gradle

allprojects {
    task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
    hello << {println "- I depend on water"}
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
I'm krill
- I depend on water
- The weight of my species in summer is twice as heavy as all human beings.

24.2.3. Project filtering

To show more of the power of configuration injection, let's add another project called tropicalFish and add more behavior to the build via the build script of the water project.

24.2.3.1. Filtering by name

Example 24.8. Adding custom behaviour to some projects (filtered by project name)

Build layout

water/
  build.gradle
  settings.gradle
  bluewhale/
    build.gradle
  krill/
    build.gradle
  tropicalFish/

Note: The code for this example can be found at samples/userguide/multiproject/addTropical/water in the ‘-all’ distribution of Gradle.

settings.gradle

include 'bluewhale', 'krill', 'tropicalFish'

build.gradle

allprojects {
    task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
    hello << {println "- I depend on water"}
}
configure(subprojects.findAll {it.name != 'tropicalFish'}) {
    hello << {println '- I love to spend time in the arctic waters.'}
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I love to spend time in the arctic waters.
- I'm the largest animal that has ever lived on this planet.
I'm krill
- I depend on water
- I love to spend time in the arctic waters.
- The weight of my species in summer is twice as heavy as all human beings.
I'm tropicalFish
- I depend on water

The configure() method takes a list as an argument and applies the configuration to the projects in this list.

24.2.3.2. Filtering by properties

Using the project name for filtering is one option. Using extra project properties is another. (See Section 16.4.2, “Extra properties” for more information on extra properties.)

Example 24.9. Adding custom behaviour to some projects (filtered by project properties)

Build layout

water/
  build.gradle
  settings.gradle
  bluewhale/
    build.gradle
  krill/
    build.gradle
  tropicalFish/
    build.gradle

Note: The code for this example can be found at samples/userguide/multiproject/tropicalWithProperties/water in the ‘-all’ distribution of Gradle.

settings.gradle

include 'bluewhale', 'krill', 'tropicalFish'

bluewhale/build.gradle

ext.arctic = true
hello.doLast {
  println "- I'm the largest animal that has ever lived on this planet."
}

krill/build.gradle

ext.arctic = true
hello.doLast {
    println "- The weight of my species in summer is twice as heavy as all human beings."
}

tropicalFish/build.gradle

ext.arctic = false

build.gradle

allprojects {
    task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
    hello {
        doLast {println "- I depend on water"}
        afterEvaluate { Project project ->
            if (project.arctic) { doLast {
                println '- I love to spend time in the arctic waters.' }
            }
        }
    }
}

Output of gradle -q hello

> gradle -q hello
I'm water
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
- I love to spend time in the arctic waters.
I'm krill
- I depend on water
- The weight of my species in summer is twice as heavy as all human beings.
- I love to spend time in the arctic waters.
I'm tropicalFish
- I depend on water

In the build file of the water project we use an afterEvaluate notification. This means that the closure we are passing gets evaluated after the build scripts of the subproject are evaluated. As the property arctic is set in those build scripts, we have to do it this way. You will find more on this topic in Section 24.6, “Dependencies - Which dependencies?”

24.3. Execution rules for multi-project builds

When we executed the hello task from the root project dir, things behaved in an intuitive way. All the hello tasks of the different projects were executed. Let's switch to the bluewhale dir and see what happens if we execute Gradle from there.

Example 24.10. Running build from subproject

Output of gradle -q hello

> gradle -q hello
I'm bluewhale
- I depend on water
- I'm the largest animal that has ever lived on this planet.
- I love to spend time in the arctic waters.

The basic rule behind Gradle's behavior is simple. Gradle looks down the hierarchy, starting with the current dir, for tasks with the name hello and executes them. One thing is very important to note. Gradle always evaluates every project of the multi-project build and creates all existing task objects. Then, according to the task name arguments and the current dir, Gradle filters the tasks which should be executed. Because of Gradle's cross project configuration every project has to be evaluated before any task gets executed. We will have a closer look at this in the next section. Let's now have our last marine example. Let's add a task to bluewhale and krill.

Example 24.11. Evaluation and execution of projects

bluewhale/build.gradle

ext.arctic = true
hello << { println "- I'm the largest animal that has ever lived on this planet." }

task distanceToIceberg << {
    println '20 nautical miles'
}

krill/build.gradle

ext.arctic = true
hello << {
    println "- The weight of my species in summer is twice as heavy as all human beings."
}

task distanceToIceberg << {
    println '5 nautical miles'
}

Output of gradle -q distanceToIceberg

> gradle -q distanceToIceberg
20 nautical miles
5 nautical miles

Here's the output without the -q option:

Example 24.12. Evaluation and execution of projects

Output of gradle distanceToIceberg

> gradle distanceToIceberg
:bluewhale:distanceToIceberg
20 nautical miles
:krill:distanceToIceberg
5 nautical miles

BUILD SUCCESSFUL

Total time: 1 secs

The build is executed from the water project. Neither water nor tropicalFish have a task with the name distanceToIceberg. Gradle does not care. The simple rule mentioned already above is: Execute all tasks down the hierarchy which have this name. Only complain if there is no such task!

24.4. Running tasks by their absolute path

As we have seen, you can run a multi-project build by entering any subproject dir and execute the build from there. All matching task names of the project hierarchy starting with the current dir are executed. But Gradle also offers to execute tasks by their absolute path (see also Section 24.5, “Project and task paths”):

Example 24.13. Running tasks by their absolute path

Output of gradle -q :hello :krill:hello hello

> gradle -q :hello :krill:hello hello
I'm water
I'm krill
- I depend on water
- The weight of my species in summer is twice as heavy as all human beings.
- I love to spend time in the arctic waters.
I'm tropicalFish
- I depend on water

The build is executed from the tropicalFish project. We execute the hello tasks of the water, the krill and the tropicalFish project. The first two tasks are specified by their absolute path, the last task is executed using the name matching mechanism described above.

24.5. Project and task paths

A project path has the following pattern: It starts with an optional colon, which denotes the root project. The root project is the only project in a path that is not specified by its name. The rest of a project path is a colon-separated sequence of project names, where the next project is a subproject of the previous project.

The path of a task is simply its project path plus the task name, like “:bluewhale:hello”. Within a project you can address a task of the same project just by its name. This is interpreted as a relative path.

24.6. Dependencies - Which dependencies?

The examples from the last section were special, as the projects had no Execution Dependencies. They had only Configuration Dependencies. The following sections illustrate the differences between these two types of dependencies.

24.6.1. Execution dependencies

24.6.1.1. Dependencies and execution order

Example 24.14. Dependencies and execution order

Build layout

messages/
  settings.gradle
  consumer/
    build.gradle
  producer/
    build.gradle

Note: The code for this example can be found at samples/userguide/multiproject/dependencies/firstMessages/messages in the ‘-all’ distribution of Gradle.

settings.gradle

include 'consumer', 'producer'

consumer/build.gradle

task action << {
    println("Consuming message: ${rootProject.producerMessage}")
}

producer/build.gradle

task action << {
    println "Producing message:"
    rootProject.producerMessage = 'Watch the order of execution.'
}

Output of gradle -q action

> gradle -q action
Consuming message: null
Producing message:

This didn't quite do what we want. If nothing else is defined, Gradle executes the task in alphanumeric order. Therefore, Gradle will execute “:consumer:action” before “:producer:action”. Let's try to solve this with a hack and rename the producer project to “aProducer”.

Example 24.15. Dependencies and execution order

Build layout

messages/
  settings.gradle
  aProducer/
    build.gradle
  consumer/
    build.gradle

settings.gradle

include 'consumer', 'aProducer'

aProducer/build.gradle

task action << {
    println "Producing message:"
    rootProject.producerMessage = 'Watch the order of execution.'
}

consumer/build.gradle

task action << {
    println("Consuming message: ${rootProject.producerMessage}")
}

Output of gradle -q action

> gradle -q action
Producing message:
Consuming message: Watch the order of execution.

We can show where this hack doesn't work if we now switch to the consumer dir and execute the build.

Example 24.16. Dependencies and execution order

Output of gradle -q action

> gradle -q action
Consuming message: null

The problem is that the two “action” tasks are unrelated. If you execute the build from the “messages” project Gradle executes them both because they have the same name and they are down the hierarchy. In the last example only one “action” task was down the hierarchy and therefore it was the only task that was executed. We need something better than this hack.

24.6.1.2. Declaring dependencies

Example 24.17. Declaring dependencies

Build layout

messages/
  settings.gradle
  consumer/
    build.gradle
  producer/
    build.gradle

Note: The code for this example can be found at samples/userguide/multiproject/dependencies/messagesWithDependencies/messages in the ‘-all’ distribution of Gradle.

settings.gradle

include 'consumer', 'producer'

consumer/build.gradle

task action(dependsOn: ":producer:action") << {
    println("Consuming message: ${rootProject.producerMessage}")
}

producer/build.gradle

task action << {
    println "Producing message:"
    rootProject.producerMessage = 'Watch the order of execution.'
}

Output of gradle -q action

> gradle -q action
Producing message:
Consuming message: Watch the order of execution.

Running this from the consumer directory gives:

Example 24.18. Declaring dependencies

Output of gradle -q action

> gradle -q action
Producing message:
Consuming message: Watch the order of execution.

This is now working better because we have declared that the “action” task in the “consumer” project has an execution dependency on the “action” task in the “producer” project.

24.6.1.3. The nature of cross project task dependencies

Of course, task dependencies across different projects are not limited to tasks with the same name. Let's change the naming of our tasks and execute the build.

Example 24.19. Cross project task dependencies

consumer/build.gradle

task consume(dependsOn: ':producer:produce') << {
    println("Consuming message: ${rootProject.producerMessage}")
}

producer/build.gradle

task produce << {
    println "Producing message:"
    rootProject.producerMessage = 'Watch the order of execution.'
}

Output of gradle -q consume

> gradle -q consume
Producing message:
Consuming message: Watch the order of execution.

24.6.2. Configuration time dependencies

Let's see one more example with our producer-consumer build before we enter Java land. We add a property to the “producer” project and create a configuration time dependency from “consumer” to “producer”.

Example 24.20. Configuration time dependencies

consumer/build.gradle

def message = rootProject.producerMessage

task consume << {
    println("Consuming message: " + message)
}

producer/build.gradle

rootProject.producerMessage = 'Watch the order of evaluation.'

Output of gradle -q consume

> gradle -q consume
Consuming message: null

The default evaluation order of projects is alphanumeric (for the same nesting level). Therefore the “consumer” project is evaluated before the “producer” project and the “producerMessage” value is set after it is read by the “consumer” project. Gradle offers a solution for this.

Example 24.21. Configuration time dependencies - evaluationDependsOn

consumer/build.gradle

evaluationDependsOn(':producer')

def message = rootProject.producerMessage

task consume << {
    println("Consuming message: " + message)
}

Output of gradle -q consume

> gradle -q consume
Consuming message: Watch the order of evaluation.

The use of the “evaluationDependsOn” command results in the evaluation of the “producer” project before the “consumer” project is evaluated. This example is a bit contrived to show the mechanism. In this case there would be an easier solution by reading the key property at execution time.

Example 24.22. Configuration time dependencies

consumer/build.gradle

task consume << {
    println("Consuming message: ${rootProject.producerMessage}")
}

Output of gradle -q consume

> gradle -q consume
Consuming message: Watch the order of evaluation.

Configuration dependencies are very different from execution dependencies. Configuration dependencies are between projects whereas execution dependencies are always resolved to task dependencies. Also note that all projects are always configured, even when you start the build from a subproject. The default configuration order is top down, which is usually what is needed.

To change the default configuration order to “bottom up”, use the “evaluationDependsOnChildren()” method instead.

On the same nesting level the configuration order depends on the alphanumeric position. The most common use case is to have multi-project builds that share a common lifecycle (e.g. all projects use the Java plugin). If you declare with dependsOn a execution dependency between different projects, the default behavior of this method is to also create a configuration dependency between the two projects. Therefore it is likely that you don't have to define configuration dependencies explicitly.

24.6.3. Real life examples

Gradle's multi-project features are driven by real life use cases. One good example consists of two web application projects and a parent project that creates a distribution including the two web applications. [14] For the example we use only one build script and do cross project configuration.

Example 24.23. Dependencies - real life example - crossproject configuration

Build layout

webDist/
  settings.gradle
  build.gradle
  date/
    src/main/java/
      org/gradle/sample/
        DateServlet.java
  hello/
    src/main/java/
      org/gradle/sample/
        HelloServlet.java

Note: The code for this example can be found at samples/userguide/multiproject/dependencies/webDist in the ‘-all’ distribution of Gradle.

settings.gradle

include 'date', 'hello'

build.gradle

allprojects {
    apply plugin: 'java'
    group = 'org.gradle.sample'
    version = '1.0'
}

subprojects {
    apply plugin: 'war'
    repositories {
        mavenCentral()
    }
    dependencies {
        compile "javax.servlet:servlet-api:2.5"
    }
}

task explodedDist(type: Copy) {
    into "$buildDir/explodedDist"
    subprojects {
        from tasks.withType(War)
    }
}

We have an interesting set of dependencies. Obviously the date and hello projects have a configuration dependency on webDist, as all the build logic for the webapp projects is injected by webDist. The execution dependency is in the other direction, as webDist depends on the build artifacts of date and hello. There is even a third dependency. webDist has a configuration dependency on date and hello because it needs to know the archivePath. But it asks for this information at execution time. Therefore we have no circular dependency.

Such dependency patterns are daily bread in the problem space of multi-project builds. If a build system does not support these patterns, you either can't solve your problem or you need to do ugly hacks which are hard to maintain and massively impair your productivity as a build master.

24.7. Project lib dependencies

What if one project needs the jar produced by another project in its compile path, and not just the jar but also the transitive dependencies of this jar? Obviously this is a very common use case for Java multi-project builds. As already mentioned in Section 23.4.3, “Project dependencies”, Gradle offers project lib dependencies for this.

Example 24.24. Project lib dependencies

Build layout

java/
  settings.gradle
  build.gradle
  api/
    src/main/java/
      org/gradle/sample/
        api/
          Person.java
        apiImpl/
          PersonImpl.java
  services/personService/
    src/
      main/java/
        org/gradle/sample/services/
          PersonService.java
      test/java/
        org/gradle/sample/services/
          PersonServiceTest.java
  shared/
    src/main/java/
      org/gradle/sample/shared/
        Helper.java

Note: The code for this example can be found at samples/userguide/multiproject/dependencies/java in the ‘-all’ distribution of Gradle.


We have the projects “shared”, “api” and “personService”. The “personService” project has a lib dependency on the other two projects. The “api” project has a lib dependency on the “shared” project. [15]

Example 24.25. Project lib dependencies

settings.gradle

include 'api', 'shared', 'services:personService'

build.gradle

subprojects {
    apply plugin: 'java'
    group = 'org.gradle.sample'
    version = '1.0'
    repositories {
        mavenCentral()
    }
    dependencies {
        testCompile "junit:junit:4.12"
    }
}

project(':api') {
    dependencies {
        compile project(':shared')
    }
}

project(':services:personService') {
    dependencies {
        compile project(':shared'), project(':api')
    }
}


All the build logic is in the “build.gradle” file of the root project. [16] A “lib” dependency is a special form of an execution dependency. It causes the other project to be built first and adds the jar with the classes of the other project to the classpath. It also adds the dependencies of the other project to the classpath. So you can enter the “api” directory and trigger a “gradle compile”. First the “shared” project is built and then the “api” project is built. Project dependencies enable partial multi-project builds.

If you come from Maven land you might be perfectly happy with this. If you come from Ivy land, you might expect some more fine grained control. Gradle offers this to you:

Example 24.26. Fine grained control over dependencies

build.gradle

subprojects {
    apply plugin: 'java'
    group = 'org.gradle.sample'
    version = '1.0'
}

project(':api') {
    configurations {
        spi
    }
    dependencies {
        compile project(':shared')
    }
    task spiJar(type: Jar) {
        baseName = 'api-spi'
        dependsOn classes
        from sourceSets.main.output
        include('org/gradle/sample/api/**')
    }
    artifacts {
        spi spiJar
    }
}

project(':services:personService') {
    dependencies {
        compile project(':shared')
        compile project(path: ':api', configuration: 'spi')
        testCompile "junit:junit:4.12", project(':api')
    }
}

The Java plugin adds per default a jar to your project libraries which contains all the classes. In this example we create an additional library containing only the interfaces of the “api” project. We assign this library to a new dependency configuration. For the person service we declare that the project should be compiled only against the “api” interfaces but tested with all classes from “api”.

24.7.1. Disabling the build of dependency projects

Sometimes you don't want depended on projects to be built when doing a partial build. To disable the build of the depended on projects you can run Gradle with the -a option.

24.8. Parallel project execution

With more and more CPU cores available on developer desktops and CI servers, it is important that Gradle is able to fully utilise these processing resources. More specifically, the parallel execution attempts to:

  • Reduce total build time for a multi-project build where execution is IO bound or otherwise does not consume all available CPU resources.
  • Provide faster feedback for execution of small projects without awaiting completion of other projects.

Although Gradle already offers parallel test execution via Test.setMaxParallelForks(int) the feature described in this section is parallel execution at a project level. Parallel execution is an incubating feature. Please use it and let us know how it works for you.

Parallel project execution allows the separate projects in a decoupled multi-project build to be executed in parallel (see also: Section 24.9, “Decoupled Projects”). While parallel execution does not strictly require decoupling at configuration time, the long-term goal is to provide a powerful set of features that will be available for fully decoupled projects. Such features include:

How does parallel execution work? First, you need to tell Gradle to use the parallel mode. You can use the command line argument (Appendix D, Gradle Command Line) or configure your build environment (Section 11.1, “Configuring the build environment via gradle.properties”). Unless you provide a specific number of parallel threads Gradle attempts to choose the right number based on available CPU cores. Every parallel worker exclusively owns a given project while executing a task. This means that 2 tasks from the same project are never executed in parallel. Therefore only multi-project builds can take advantage of parallel execution. Task dependencies are fully supported and parallel workers will start executing upstream tasks first. Bear in mind that the alphabetical scheduling of decoupled tasks, known from the sequential execution, does not really work in parallel mode. You need to make sure the task dependencies are declared correctly to avoid ordering issues.

24.9. Decoupled Projects

Gradle allows any project to access any other project during both the configuration and execution phases. While this provides a great deal of power and flexibility to the build author, it also limits the flexibility that Gradle has when building those projects. For instance, this effectively prevents Gradle from correctly building multiple projects in parallel, configuring only a subset of projects, or from substituting a pre-built artifact in place of a project dependency.

Two projects are said to be decoupled if they do not directly access each other's project model. Decoupled projects may only interact in terms of declared dependencies: project dependencies (Section 23.4.3, “Project dependencies”) and/or task dependencies (Section 14.5, “Task dependencies”). Any other form of project interaction (i.e. by modifying another project object or by reading a value from another project object) causes the projects to be coupled. The consequence of coupling during the configuration phase is that if gradle is invoked with the 'configuration on demand' option, the result of the build can be flawed in several ways. The consequence of coupling during execution phase is that if gradle is invoked with the parallel option, one project task runs too late to influence a task of a project building in parallel. Gradle does not attempt to detect coupling and warn the user, as there are too many possibilities to introduce coupling.

A very common way for projects to be coupled is by using configuration injection (Section 24.1, “Cross project configuration”). It may not be immediately apparent, but using key Gradle features like the allprojects and subprojects keywords automatically cause your projects to be coupled. This is because these keywords are used in a build.gradle file, which defines a project. Often this is a “root project” that does nothing more than define common configuration, but as far as Gradle is concerned this root project is still a fully-fledged project, and by using allprojects that project is effectively coupled to all other projects. Coupling of the root project to subprojects does not impact 'configuration on demand', but using the allprojects and subprojects in any subproject's build.gradle file will have an impact.

This means that using any form of shared build script logic or configuration injection (allprojects, subprojects, etc.) will cause your projects to be coupled. As we extend the concept of project decoupling and provide features that take advantage of decoupled projects, we will also introduce new features to help you to solve common use cases (like configuration injection) without causing your projects to be coupled.

In order to make good use of cross project configuration without running into issues for parallel and 'configuration on demand' options, follow these recommendations:

  • Avoid a subproject's build.gradle referencing other subprojects; prefering cross configuration from the root project.
  • Avoid changing the configuration of other projects at execution time.

24.10. Multi-Project Building and Testing

The build task of the Java plugin is typically used to compile, test, and perform code style checks (if the CodeQuality plugin is used) of a single project. In multi-project builds you may often want to do all of these tasks across a range of projects. The buildNeeded and buildDependents tasks can help with this.

Look at Example 24.25, “Project lib dependencies”. In this example, the “:services:personservice” project depends on both the “:api” and “:shared” projects. The “:api” project also depends on the “:shared” project.

Assume you are working on a single project, the “:api” project. You have been making changes, but have not built the entire project since performing a clean. You want to build any necessary supporting jars, but only perform code quality and unit tests on the project you have changed. The build task does this.

Example 24.27. Build and Test Single Project

Output of gradle :api:build

> gradle :api:build
:shared:compileJava
:shared:processResources
:shared:classes
:shared:jar
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build

BUILD SUCCESSFUL

Total time: 1 secs

While you are working in a typical development cycle repeatedly building and testing changes to the “:api” project (knowing that you are only changing files in this one project), you may not want to even suffer the expense of building “:shared:compile” to see what has changed in the “:shared” project. Adding the “-a” option will cause Gradle to use cached jars to resolve any project lib dependencies and not try to re-build the depended on projects.

Example 24.28. Partial Build and Test Single Project

Output of gradle -a :api:build

> gradle -a :api:build
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build

BUILD SUCCESSFUL

Total time: 1 secs

If you have just gotten the latest version of source from your version control system which included changes in other projects that “:api” depends on, you might want to not only build all the projects you depend on, but test them as well. The buildNeeded task also tests all the projects from the project lib dependencies of the testRuntime configuration.

Example 24.29. Build and Test Depended On Projects

Output of gradle :api:buildNeeded

> gradle :api:buildNeeded
:shared:compileJava
:shared:processResources
:shared:classes
:shared:jar
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build
:shared:assemble
:shared:compileTestJava
:shared:processTestResources
:shared:testClasses
:shared:test
:shared:check
:shared:build
:shared:buildNeeded
:api:buildNeeded

BUILD SUCCESSFUL

Total time: 1 secs

You also might want to refactor some part of the “:api” project that is used in other projects. If you make these types of changes, it is not sufficient to test just the “:api” project, you also need to test all projects that depend on the “:api” project. The buildDependents task also tests all the projects that have a project lib dependency (in the testRuntime configuration) on the specified project.

Example 24.30. Build and Test Dependent Projects

Output of gradle :api:buildDependents

> gradle :api:buildDependents
:shared:compileJava
:shared:processResources
:shared:classes
:shared:jar
:api:compileJava
:api:processResources
:api:classes
:api:jar
:api:assemble
:api:compileTestJava
:api:processTestResources
:api:testClasses
:api:test
:api:check
:api:build
:services:personService:compileJava
:services:personService:processResources
:services:personService:classes
:services:personService:jar
:services:personService:assemble
:services:personService:compileTestJava
:services:personService:processTestResources
:services:personService:testClasses
:services:personService:test
:services:personService:check
:services:personService:build
:services:personService:buildDependents
:api:buildDependents

BUILD SUCCESSFUL

Total time: 1 secs

Finally, you may want to build and test everything in all projects. Any task you run in the root project folder will cause that same named task to be run on all the children. So you can just run “gradle build” to build and test all projects.

24.11. Multi Project and buildSrc

Section 41.4, “Build sources in the buildSrc project” tells us that we can place build logic to be compiled and tested in the special buildSrc directory. In a multi project build, there can only be one buildSrc directory which must be located in the root directory.

24.12. Property and method inheritance

Properties and methods declared in a project are inherited to all its subprojects. This is an alternative to configuration injection. But we think that the model of inheritance does not reflect the problem space of multi-project builds very well. In a future edition of this user guide we might write more about this.

Method inheritance might be interesting to use as Gradle's Configuration Injection does not support methods yet (but will in a future release).

You might be wondering why we have implemented a feature we obviously don't like that much. One reason is that it is offered by other tools and we want to have the check mark in a feature comparison :). And we like to offer our users a choice.

24.13. Summary

Writing this chapter was pretty exhausting and reading it might have a similar effect. Our final message for this chapter is that multi-project builds with Gradle are usually not difficult. There are five elements you need to remember: allprojects, subprojects, evaluationDependsOn, evaluationDependsOnChildren and project lib dependencies. [17] With those elements, and keeping in mind that Gradle has a distinct configuration and execution phase, you already have a lot of flexibility. But when you enter steep territory Gradle does not become an obstacle and usually accompanies and carries you to the top of the mountain.



[14] The real use case we had, was using http://lucene.apache.org/solr, where you need a separate war for each index you are accessing. That was one reason why we have created a distribution of webapps. The Resin servlet container allows us, to let such a distribution point to a base installation of the servlet container.

[15] services” is also a project, but we use it just as a container. It has no build script and gets nothing injected by another build script.

[16] We do this here, as it makes the layout a bit easier. We usually put the project specific stuff into the build script of the respective projects.

[17] So we are well in the range of the 7 plus 2 Rule :)

Chapter 25. Gradle Plugins

Gradle at its core intentionally provides very little for real world automation. All of the useful features, like the ability to compile Java code, are added by plugins. Plugins add new tasks (e.g. JavaCompile), domain objects (e.g. SourceSet), conventions (e.g. Java source is located at src/main/java) as well as extending core objects and objects from other plugins.

In this chapter we will discuss how to use plugins and the terminology and concepts surrounding plugins.

25.1. What plugins do

Applying a plugin to a project allows the plugin to extend the project's capabilities. It can do things such as:

  • Extend the Gradle model (e.g. add new DSL elements that can be configured)
  • Configure the project according to conventions (e.g. add new tasks or configure sensible defaults)
  • Apply specific configuration (e.g. add organizational repositories or enforce standards)

By applying plugins, rather than adding logic to the project build script, we can reap a number of benefits. Applying plugins:

  • Promotes reuse and reduces the overhead of maintaining similar logic across multiple projects
  • Allows a higher degree of modularization, enhancing comprehensibility and organization
  • Encapsulates imperative logic and allows build scripts to be as declarative as possible

25.2. Types of plugins

There are two general types of plugins in Gradle, script plugins and binary plugins. Script plugins are additional build scripts that further configure the build and usually implement a declarative approach to manipulating the build. They are typically used within a build although they can be externalized and accessed from a remote location. Binary plugins are classes that implement the Plugin interface and adopt a programmatic approach to manipulating the build. Binary plugins can reside within a build script, within the project hierarchy or externally in a plugin jar.

25.3. Applying plugins

Plugins are said to be applied, which is done via the Project.apply(java.util.Map) method. The application of plugins is idempotent. That is, the same plugin can be applied multiple times. If the plugin has previously been applied, any further applications are safe and will have no effect.

25.3.1. Script plugins

Example 25.1. Applying a script plugin

build.gradle

apply from: 'other.gradle'

Script plugins can be applied from a script on the local filesystem or at a remote location. Filesystem locations are relative to the project directory, while remote script locations are specified with an HTTP URL. Multiple script plugins (of either form) can be applied to a given build.

25.3.2. Binary plugins

Example 25.2. Applying a binary plugin

build.gradle

apply plugin: 'java'

Plugins can be applied using a plugin id. The plugin id serves as a unique identifier for a given plugin. Core plugins register a short name that can be used as the plugin id. In the above case, we are using the short name ‘java’ to apply the JavaPlugin. Community plugins, on the other hand, use a fully qualified form for the plugin id (e.g. com.github.foo.bar), although some legacy plugins may still utilize a short, unqualified form.

Rather than using a plugin id, plugins can also be applied by simply specifying the class of the plugin:

Example 25.3. Applying a binary plugin by type

build.gradle

apply plugin: JavaPlugin

The JavaPlugin symbol in the above sample refers to the the JavaPlugin. This class does not strictly need to be imported as the org.gradle.api.plugins package is automatically imported in all build scripts (see Section 16.8, “Default imports”). Furthermore, it is not necessary to append .class to identify a class literal in Groovy as it is in Java.

25.3.2.1. Locations of binary plugins

A plugin is simply any class that implements the Plugin interface. Gradle provides the core plugins as part of its distribution so simply applying the plugin as above is all you need to do. However, non-core binary plugins need to be available to the build classpath before they can be applied. This can be achieved in a number of ways, including:

For more on defining your own plugins, see Chapter 39, Writing Custom Plugins.

25.4. Applying plugins with the buildscript block

Binary plugins that have been published as external jar files can be added to a project by adding the plugin to the build script classpath and then applying the plugin. External jars can be added to the build script classpath using the buildscript {} block as described in Section 41.6, “External dependencies for the build script”.

Example 25.4. Applying a plugin with the buildscript block

build.gradle

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath "com.jfrog.bintray.gradle:gradle-bintray-plugin:0.4.1"
    }
}

apply plugin: "com.jfrog.bintray"

25.5. Applying plugins with the plugins DSL

The plugins DSL is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The new plugins DSL provides a more succinct and convenient way to declare plugin dependencies. It works with the new Gradle plugin portal to provide easy access to both core and community plugins. The plugins script block configures an instance of PluginDependenciesSpec.

To apply a core plugin, the short name can be used:

Example 25.5. Applying a core plugin

build.gradle

plugins {
    id 'java'
}

To apply a community plugin from the portal, the fully qualified plugin id must be used:

Example 25.6. Applying a community plugin

build.gradle

plugins {
    id "com.jfrog.bintray" version "0.4.1"
}

No further configuration is necessary. Specifically, there is no need to configure the buildscript classpath. Gradle will resolve the plugin in the plugin portal, locate it, and make it available to the build.

See PluginDependenciesSpec for more information on using the Plugin DSL.

25.5.1. Limitations of the plugins DSL

The new way to add plugins to a project is much more than a more convenient syntax. The new DSL is processed very differently to the old one. The new mechanism allows Gradle to determine the plugins in use very early and very quickly. This allows Gradle to do smart things such as:

  • Optimize the loading and reuse of plugin classes.
  • Allow different plugins to use different versions of dependencies.
  • Provide editors detailed information about the potential properties and values in the buildscript for editing assistance.

This requires that plugins be specified in a way that Gradle can easily and quickly extract, before executing the rest of the build script. It also requires that the definition of plugins to use be somewhat static.

There are some key differences between the new plugin mechanism and the “traditional” apply() method mechanism. There are also some constraints, some of which are temporary limitations while the mechanism is still being developed and some are inherent to the new approach.

25.5.1.1. Constrained Syntax

The new plugins {} block does not support arbitrary Groovy code. It is constrained, in order to be idempotent (produce the same result every time) and side effect free (safe for Gradle to execute at any time).

The form is:

plugins {
    id «plugin id» version «plugin version»
}
                

Where «plugin version» and «plugin id» must be constant, literal, strings. No other statements are allowed; their presence will cause a compilation error.

The plugins {} block must also be a top level statement in the buildscript. It cannot be nested inside another construct (e.g. an if-statement or for-loop).

25.5.1.2. Can only be used in build scripts

The plugins {} block can currently only be used in a project's build script. It cannot be used in script plugins, the settings.gradle file or init scripts.

Future versions of Gradle will remove this restriction.

25.5.1.3. Cannot be used in conjunction with subprojects {}, allprojects {}, etc

It is not possible to use the familiar pattern of applying a plugin to multiple projects at once using subprojects {}, etc at the moment. There is currently no mechanism for applying a plugin to multiple projects at once. At the moment, each project that requires a plugin must declare so in the plugins {} block in its buildscript.

Future versions of Gradle will remove this restriction.

If the restrictions of the new syntax are prohibitive, the recommended approach is to apply plugins using the buildscript {} block.

25.6. Custom Plugin Repositories

The pluginRepositories {} DSL is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

By default, the plugins {} DSL resolves plugins from the public Gradle Plugin Portal. Many build authors would also like to resolve plugins from private Maven or Ivy repositories because the plugins contain proprietary implementation details, or just to have more control over what plugins are available to their builds.

To specify custom plugin repositories, add a pluginRepositories {} block to the settings.gradle file:

Example 25.7. Using plugins from custom plugin repositories.

settings.gradle

pluginRepositories {
  maven {
    url 'maven-repo'
  }
  gradlePluginPortal()
  ivy {
    url 'ivy-repo'
  }
}

This tells Gradle to first look in the Maven repository at maven-repo when resolving plugins and then to check the Gradle Plugin Portal if the plugins are not found in the Maven repository. If you don't want the Gradle Plugin Portal to be searched, omit the gradlePluginPortal() line. Finally, the Ivy repository at ivy-repo will be checked.

The pluginRepositories {} block may only appear in the settings.gradle file, and must be the first block in the file. Custom Maven and Ivy plugin repositories must contain plugin marker artifacts in addition to the artifacts which actually implement the plugin. For more information on publishing plugins to custom repositories read Chapter 40, The Java Gradle Plugin Development Plugin.

See PluginRepositoriesSpec for complete documentation for using the pluginRepositories {} block.

25.7. Plugin Marker Artifacts

Since the plugins {} DSL block only allows for declaring plugins by their globally unique plugin id and version properties, Gradle needs a way to look up the coordinates of the plugin implementation artifact. To do so, Gradle will look for a Plugin Marker Artifact with the coordinates plugin.id:plugin.id.gradle.plugin:plugin.version. This marker needs to have a dependency on the actual plugin implementation. Publishing these markers is automated by the java-gradle-plugin.

For example, the following complete sample from the sample-plugins project shows how to publish a org.gradle.sample.hello plugin and a org.gradle.sample.goodbye plugin to both an Ivy and Maven repository using the combination of the java-gradle-plugin, the maven-publish plugin, and the ivy-publish plugin.

Example 25.8. Complete Plugin Publishing Sample

build.gradle

plugins {
  id 'java-gradle-plugin'
  id 'maven-publish'
  id 'ivy-publish'
}

group 'org.gradle.sample'
version '1.0.0'

gradlePlugin {
  plugins {
    hello {
      id = "org.gradle.sample.hello"
      implementationClass = "org.gradle.sample.hello.HelloPlugin"
    }
    goodbye {
      id = "org.gradle.sample.goodbye"
      implementationClass = "org.gradle.sample.goodbye.GoodbyePlugin"
    }
  }
}

publishing {
  repositories {
    maven {
      url "../consuming/maven-repo"
    }
    ivy {
      url "../consuming/ivy-repo"
    }
  }
}

Running gradle publish in the sample directory causes the following repo layouts to exist:

25.8. Finding community plugins

Gradle has a vibrant community of plugin developers who contribute plugins for a wide variety of capabilities. The Gradle plugin portal provides an interface for searching and exploring community plugins.

25.9. More on plugins

This chapter aims to serve as an introduction to plugins and Gradle and the role they play. For more information on the inner workings of plugins, see Chapter 39, Writing Custom Plugins.

Chapter 26. Standard Gradle plugins

There are a number of plugins included in the Gradle distribution. These are listed below.

26.1. Language plugins

These plugins add support for various languages which can be compiled for and executed in the JVM.

Table 26.1. Language plugins

Plugin Id Automatically applies Works with Description
java java-base -

Adds Java compilation, testing and bundling capabilities to a project. It serves as the basis for many of the other Gradle plugins. See also Chapter 44, Java Quickstart.

groovy java, groovy-base -

Adds support for building Groovy projects. See also Chapter 52, Groovy Quickstart.

scala java, scala-base -

Adds support for building Scala projects.

antlr java -

Adds support for generating parsers using Antlr.

26.2. Incubating language plugins

These plugins add support for various languages:

Table 26.2. Language plugins

Plugin Id Automatically applies Works with Description
assembler - -

Adds native assembly language capabilities to a project.

c - -

Adds C source compilation capabilities to a project.

cpp - -

Adds C++ source compilation capabilities to a project.

objective-c - -

Adds Objective-C source compilation capabilities to a project.

objective-cpp - -

Adds Objective-C++ source compilation capabilities to a project.

windows-resources - -

Adds support for including Windows resources in native binaries.

26.3. Integration plugins

These plugins provide some integration with various runtime technologies.

Table 26.3. Integration plugins

Plugin Id Automatically applies Works with Description
application java, distribution -

Adds tasks for running and bundling a Java project as a command-line application.

ear - java

Adds support for building J2EE applications.

jetty war -

Deploys your web application to a Jetty web container embedded in the build. See also Chapter 46, Web Application Quickstart.

maven - java, war

Adds support for publishing artifacts to Maven repositories.

osgi java-base java

Adds support for building OSGi bundles.

war java -

Adds support for assembling web application WAR files. See also Chapter 46, Web Application Quickstart.

26.4. Incubating integration plugins

These plugins provide some integration with various runtime technologies.

Table 26.4. Incubating integration plugins

Plugin Id Automatically applies Works with Description
distribution - -

Adds support for building ZIP and TAR distributions.

java-library-distribution java, distribution -

Adds support for building ZIP and TAR distributions for a Java library.

ivy-publish - java, war

This plugin provides a new DSL to support publishing artifacts to Ivy repositories, which improves on the existing DSL.

maven-publish - java, war

This plugin provides a new DSL to support publishing artifacts to Maven repositories, which improves on the existing DSL.

26.5. Software development plugins

These plugins provide help with your software development process.

Table 26.5. Software development plugins

Plugin Id Automatically applies Works with Description
announce - -

Publish messages to your favourite platforms, such as Twitter or Growl.

build-announcements announce -

Sends local announcements to your desktop about interesting events in the build lifecycle.

checkstyle java-base -

Performs quality checks on your project's Java source files using Checkstyle and generates reports from these checks.

codenarc groovy-base -

Performs quality checks on your project's Groovy source files using CodeNarc and generates reports from these checks.

eclipse - java,groovy, scala

Generates files that are used by Eclipse IDE, thus making it possible to import the project into Eclipse. See also Chapter 44, Java Quickstart.

eclipse-wtp - ear, war

Does the same as the eclipse plugin plus generates eclipse WTP (Web Tools Platform) configuration files. After importing to eclipse your war/ear projects should be configured to work with WTP. See also Chapter 44, Java Quickstart.

findbugs java-base -

Performs quality checks on your project's Java source files using FindBugs and generates reports from these checks.

idea - java

Generates files that are used by Intellij IDEA IDE, thus making it possible to import the project into IDEA.

jdepend java-base -

Performs quality checks on your project's source files using JDepend and generates reports from these checks.

pmd java-base -

Performs quality checks on your project's Java source files using PMD and generates reports from these checks.

project-report reporting-base -

Generates reports containing useful information about your Gradle build.

signing base -

Adds the ability to digitally sign built files and artifacts.

sonar - java-base, java, jacoco

Provides integration with the Sonar code quality platform. Superceeded by the sonar-runner plugin.

26.6. Incubating software development plugins

These plugins provide help with your software development process.

Table 26.6. Software development plugins

Plugin Id Automatically applies Works with Description
build-dashboard reporting-base -

Generates build dashboard report.

build-init wrapper -

Adds support for initializing a new Gradle build. Handles converting a Maven build to a Gradle build.

cunit - -

Adds support for running CUnit tests.

jacoco reporting-base java

Provides integration with the JaCoCo code coverage library for Java.

sonar-runner - java-base, java, jacoco

Provides integration with the Sonar code quality platform. Supersedes the sonar plugin.

visual-studio - native language plugins

Adds integration with Visual Studio.

wrapper - -

Adds a Wrapper task for generating Gradle wrapper files.

java-gradle-plugin java

Assists with development of Gradle plugins by providing standard plugin build configuration and validation.

26.7. Base plugins

These plugins form the basic building blocks which the other plugins are assembled from. They are available for you to use in your build files, and are listed here for completeness. However, be aware that they are not yet considered part of Gradle's public API. As such, these plugins are not documented in the user guide. You might refer to their API documentation to learn more about them.

Table 26.7. Base plugins

Plugin Id Description
base

Adds the standard lifecycle tasks and configures reasonable defaults for the archive tasks:

  • adds build ConfigurationName tasks. Those tasks assemble the artifacts belonging to the specified configuration.
  • adds upload ConfigurationName tasks. Those tasks assemble and upload the artifacts belonging to the specified configuration.
  • configures reasonable default values for all archive tasks (e.g. tasks that inherit from AbstractArchiveTask). For example, the archive tasks are tasks of types: Jar, Tar, Zip. Specifically, destinationDir, baseName and version properties of the archive tasks are preconfigured with defaults. This is extremely useful because it drives consistency across projects; the consistency regarding naming conventions of archives and their location after the build completed.

java-base

Adds the source sets concept to the project. Does not add any particular source sets.

groovy-base

Adds the Groovy source sets concept to the project.

scala-base

Adds the Scala source sets concept to the project.

reporting-base

Adds some shared convention properties to the project, relating to report generation.

26.8. Third party plugins

You can find a list of external plugins at the Gradle Plugins site.

Chapter 27. The Project Report Plugin

The Project report plugin adds some tasks to your project which generate reports containing useful information about your build. These tasks generate the same content that you get by executing the tasks, dependencies, and properties tasks from the command line (see Section 4.7, “Obtaining information about your build”). In contrast to the command line reports, the report plugin generates the reports into a file. There is also an aggregating task that depends on all report tasks added by the plugin.

We plan to add much more to the existing reports and create additional ones in future releases of Gradle.

27.1. Usage

To use the Project report plugin, include the following in your build script:

apply plugin: 'project-report'

27.2. Tasks

The project report plugin defines the following tasks:

Table 27.1. Project report plugin - tasks

Task name Depends on Type Description
dependencyReport - DependencyReportTask Generates the project dependency report.
htmlDependencyReport - HtmlDependencyReportTask Generates an HTML dependency and dependency insight report for the project or a set of projects.
propertyReport - PropertyReportTask Generates the project property report.
taskReport - TaskReportTask Generates the project task report.
projectReport dependencyReport, propertyReport, taskReport, htmlDependencyReport Task Generates all project reports.

27.3. Project layout

The project report plugin does not require any particular project layout.

27.4. Dependency management

The project report plugin does not define any dependency configurations.

27.5. Convention properties

The project report defines the following convention properties:

Table 27.2. Project report plugin - convention properties

Property name Type Default value Description
reportsDirName String reports The name of the directory to generate reports into, relative to the build directory.
reportsDir File (read-only) buildDir/reportsDirName The directory to generate reports into.
projects Set<Project> A one element set with the project the plugin was applied to. The projects to generate the reports for.
projectReportDirName String project The name of the directory to generate the project report into, relative to the reports directory.
projectReportDir File (read-only) reportsDir/projectReportDirName The directory to generate the project report into.

These convention properties are provided by a convention object of type ProjectReportsPluginConvention.

Chapter 28. The Build Dashboard Plugin

The build dashboard plugin is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The Build Dashboard plugin can be used to generate a single HTML dashboard that provides a single point of access to all of the reports generated by a build.

28.1. Usage

To use the Build Dashboard plugin, include the following in your build script:

Example 28.1. Using the Build Dashboard plugin

build.gradle

apply plugin: 'build-dashboard'

Applying the plugin adds the buildDashboard task to your project. The task aggregates the reports for all tasks that implement the Reporting interface from all projects in the build. It is typically only applied to the root project.

The buildDashboard task does not depend on any other tasks. It will only aggregate the reporting tasks that are independently being executed as part of the build run. To generate the build dashboard, simply include this task in the list of tasks to execute. For example, “gradle buildDashboard build” will generate a dashboard for all of the reporting tasks that are dependents of the build task.

28.2. Tasks

The Build Dashboard plugin adds the following task to the project:

Table 28.1. Build Dashboard plugin - tasks

Task name Depends on Type Description
buildDashboard - GenerateBuildDashboard Generates build dashboard report.

28.3. Project layout

The Build Dashboard plugin does not require any particular project layout.

28.4. Dependency management

The Build Dashboard plugin does not define any dependency configurations.

28.5. Configuration

You can influence the location of build dashboard plugin generation via ReportingExtension.

Chapter 29. Comparing Builds

Build comparison support is an incubating feature. This means that it is incomplete and not yet at regular Gradle production quality. This also means that this Gradle User Guide chapter is a work in progress.

Gradle provides support for comparing the outcomes (e.g. the produced binary archives) of two builds. There are several reasons why you may want to compare the outcomes of two builds. You may want to compare:

  • A build with a newer version of Gradle than it's currently using (i.e. upgrading the Gradle version).

  • A Gradle build with a build executed by another tool such as Apache Ant, Apache Maven or something else (i.e. migrating to Gradle).

  • The same Gradle build, with the same version, before and after a change to the build (i.e. testing build changes).

By comparing builds in these scenarios you can make an informed decision about the Gradle upgrade, migration to Gradle or build change by understanding the differences in the outcomes. The comparison process produces a HTML report outlining which outcomes were found to be identical and identifying the differences between non-identical outcomes.

29.1. Definition of terms

The following are the terms used for build comparison and their definitions.

“Build”

In the context of build comparison, a build is not necessarily a Gradle build. It can be any invokable “process” that produces observable “outcomes”. At least one of the builds in a comparison will be a Gradle build.

“Build Outcome”

Something that happens in an observable manner during a build, such as the creation of a zip file or test execution. These are the things that are compared.

“Source Build”

The build that comparisons are being made against, typically the build in its “current” state. In other words, the left hand side of the comparison.

“Target Build”

The build that is being compared to the source build, typically the “proposed” build. In other words, the right hand side of the comparison.

“Host Build”

The Gradle build that executes the comparison process. It may be the same project as either the “target” or “source” build or may be a completely separate project. It does not need to be the same Gradle version as the “source” or “target” builds. The host build must be run with Gradle 1.2 or newer.

“Compared Build Outcome”

Build outcomes that are intended to be logically equivalent in the “source” and “target” builds, and are therefore meaningfully comparable.

“Uncompared Build Outcome”

A build outcome is uncompared if a logical equivalent from the other build cannot be found (e.g. a build produces a zip file that the other build does not).

“Unknown Build Outcome”

A build outcome that cannot be understood by the host build. This can occur when the source or target build is a newer Gradle version than the host build and that Gradle version exposes new outcome types. Unknown build outcomes can be compared in so far as they can be identified to be logically equivalent to an unknown build outcome in the other build, but no meaningful comparison of what the build outcome actually is can be performed. Using the latest Gradle version for the host build will avoid encountering unknown build outcomes.

29.2. Current Capabilities

As this is an incubating feature, a limited set of the eventual functionality has been implemented at this time.

29.2.1. Supported builds

Only support for comparing Gradle builds is available at this time. Both the source and target build must execute with Gradle newer or equal to version 1.0. The host build must be at least version 1.2.

Future versions will provide support for executing builds from other build systems such as Apache Ant or Apache Maven, as well as support for executing arbitrary processes (e.g. shell script based builds)

29.2.2. Supported build outcomes

Only support for comparing build outcomes that are zip archives is supported at this time. This includes jar, war and ear archives.

Future versions will provide support for comparing outcomes such as test execution (i.e. which tests were executed, which tests failed, etc.)

29.3. Comparing Gradle Builds

The compare-gradle-builds plugin can be used to facilitate a comparison between two Gradle builds. The plugin adds a CompareGradleBuilds task named “compareGradleBuilds” to the project. The configuration of this task specifies what is to be compared. By default, it is configured to compare the current build with itself using the current Gradle version by executing the tasks: “clean assemble”.

apply plugin: 'compare-gradle-builds'

This task can be configured to change what is compared.

compareGradleBuilds {
    sourceBuild {
        projectDir "/projects/project-a"
        gradleVersion "1.1"
    }
    targetBuild {
        projectDir "/projects/project-b"
        gradleVersion "1.2"
    }
}
        

The example above specifies a comparison between two different projects using two different Gradle versions.

29.3.1. Trying Gradle upgrades

You can use the build comparison functionality to very quickly try a new Gradle version with your build.

To try your current build with a different Gradle version, simply add the following to the build.gradle of the root project.

apply plugin: 'compare-gradle-builds'

compareGradleBuilds {
    targetBuild.gradleVersion = "«gradle version»"
}
            

Then simply execute the compareGradleBuilds task. You will see the console output of the “source” and “target” builds as they are executing.

29.3.2. The comparison “result”

If there are any differences between the compared outcomes, the task will fail. The location of the HTML report providing insight into the comparison will be given. If all compared outcomes are found to be identical, and there are no uncompared outcomes, and there are no unknown build outcomes, the task will succeed.

You can configure the task to not fail on compared outcome differences by setting the ignoreFailures property to true.

compareGradleBuilds {
    ignoreFailures = true
}
            

29.3.3. Which archives are compared?

For an archive to be a candidate for comparison, it must be added as an artifact of the archives configuration. Take a look at Chapter 30, Publishing artifacts for more information on how to configure and add artifacts.

The archive must also have been produced by a Zip, Jar, War, Ear task. Future versions of Gradle will support increased flexibility in this area.

Chapter 30. Publishing artifacts

This chapter describes the original publishing mechanism available in Gradle 1.0: in Gradle 1.3 a new mechanism for publishing was introduced. While this new mechanism is incubating and not yet complete, it introduces some new concepts and features that do (and will) make Gradle publishing even more powerful.

You can read about the new publishing plugins in Chapter 33, Ivy Publishing (new) and Chapter 34, Maven Publishing (new). Please try them out and give us feedback.

30.1. Introduction

This chapter is about how you declare the outgoing artifacts of your project, and how to work with them (e.g. upload them). We define the artifacts of the projects as the files the project provides to the outside world. This might be a library or a ZIP distribution or any other file. A project can publish as many artifacts as it wants.

30.2. Artifacts and configurations

Like dependencies, artifacts are grouped by configurations. In fact, a configuration can contain both artifacts and dependencies at the same time.

For each configuration in your project, Gradle provides the tasks uploadConfigurationName and buildConfigurationName. [18] Execution of these tasks will build or upload the artifacts belonging to the respective configuration.

Table 45.5, “Java plugin - dependency configurations” shows the configurations added by the Java plugin. Two of the configurations are relevant for the usage with artifacts. The archives configuration is the standard configuration to assign your artifacts to. The Java plugin automatically assigns the default jar to this configuration. We will talk more about the runtime configuration in Section 30.5, “More about project libraries”. As with dependencies, you can declare as many custom configurations as you like and assign artifacts to them.

30.3. Declaring artifacts

30.3.1. Archive task artifacts

You can use an archive task to define an artifact:

Example 30.1. Defining an artifact using an archive task

build.gradle

task myJar(type: Jar)

artifacts {
    archives myJar
}

It is important to note that the custom archives you are creating as part of your build are not automatically assigned to any configuration. You have to explicitly do this assignment.

30.3.2. File artifacts

You can also use a file to define an artifact:

Example 30.2. Defining an artifact using a file

build.gradle

def someFile = file('build/somefile.txt')

artifacts {
    archives someFile
}

Gradle will figure out the properties of the artifact based on the name of the file. You can customize these properties:

Example 30.3. Customizing an artifact

build.gradle

task myTask(type:  MyTaskType) {
    destFile = file('build/somefile.txt')
}

artifacts {
    archives(myTask.destFile) {
        name 'my-artifact'
        type 'text'
        builtBy myTask
    }
}

There is a map-based syntax for defining an artifact using a file. The map must include a file entry that defines the file. The map may include other artifact properties:

Example 30.4. Map syntax for defining an artifact using a file

build.gradle

task generate(type:  MyTaskType) {
    destFile = file('build/somefile.txt')
}

artifacts {
    archives file: generate.destFile, name: 'my-artifact', type: 'text', builtBy: generate
}

30.4. Publishing artifacts

We have said that there is a specific upload task for each configuration. Before you can do an upload, you have to configure the upload task and define where to publish the artifacts to. The repositories you have defined (as described in Section 23.6, “Repositories”) are not automatically used for uploading. In fact, some of those repositories only allow downloading artifacts, not uploading. Here is an example of how you can configure the upload task of a configuration:

Example 30.5. Configuration of the upload task

build.gradle

repositories {
    flatDir {
        name "fileRepo"
        dirs "repo"
    }
}

uploadArchives {
    repositories {
        add project.repositories.fileRepo
        ivy {
            credentials {
                username "username"
                password "pw"
            }
            url "http://repo.mycompany.com"
        }
    }
}

As you can see, you can either use a reference to an existing repository or create a new repository. As described in Section 23.6.9, “More about Ivy resolvers”, you can use all the Ivy resolvers suitable for the purpose of uploading.

If an upload repository is defined with multiple patterns, Gradle must choose a pattern to use for uploading each file. By default, Gradle will upload to the pattern defined by the url parameter, combined with the optional layout parameter. If no url parameter is supplied, then Gradle will use the first defined artifactPattern for uploading, or the first defined ivyPattern for uploading Ivy files, if this is set.

Uploading to a Maven repository is described in Section 31.6, “Interacting with Maven repositories”.

30.5. More about project libraries

If your project is supposed to be used as a library, you need to define what are the artifacts of this library and what are the dependencies of these artifacts. The Java plugin adds a runtime configuration for this purpose, with the implicit assumption that the runtime dependencies are the dependencies of the artifact you want to publish. Of course this is fully customizable. You can add your own custom configuration or let the existing configurations extend from other configurations. You might have a different group of artifacts which have a different set of dependencies. This mechanism is very powerful and flexible.

If someone wants to use your project as a library, she simply needs to declare which configuration of the dependency to depend on. A Gradle dependency offers the configuration property to declare this. If this is not specified, the default configuration is used (see Section 23.4.9, “Dependency configurations”). Using your project as a library can either happen from within a multi-project build or by retrieving your project from a repository. In the latter case, an ivy.xml descriptor in the repository is supposed to contain all the necessary information. If you work with Maven repositories you don't have the flexibility as described above. For how to publish to a Maven repository, see the section Section 31.6, “Interacting with Maven repositories”.



[18] To be exact, the Base plugin provides those tasks. This plugin is automatically applied if you use the Java plugin.

Chapter 31. The Maven Plugin

This chapter is a work in progress

The Maven plugin adds support for deploying artifacts to Maven repositories.

31.1. Usage

To use the Maven plugin, include the following in your build script:

Example 31.1. Using the Maven plugin

build.gradle

apply plugin: 'maven'

31.2. Tasks

The Maven plugin defines the following tasks:

Table 31.1. Maven plugin - tasks

Task name Depends on Type Description
install All tasks that build the associated archives. Upload Installs the associated artifacts to the local Maven cache, including Maven metadata generation. By default the install task is associated with the archives configuration. This configuration has by default only the default jar as an element. To learn more about installing to the local repository, see: Section 31.6.3, “Installing to the local repository”

31.3. Dependency management

The Maven plugin does not define any dependency configurations.

31.4. Convention properties

The Maven plugin defines the following convention properties:

Table 31.2. Maven plugin - properties

Property name Type Default value Description
mavenPomDir File ${project.buildDir}/poms The directory where the generated POMs are written to.
conf2ScopeMappings Conf2ScopeMappingContainer n/a Instructions for mapping Gradle configurations to Maven scopes. See Section 31.6.4.2, “Dependency mapping”.

These properties are provided by a MavenPluginConvention convention object.

31.5. Convention methods

The maven plugin provides a factory method for creating a POM. This is useful if you need a POM without the context of uploading to a Maven repo.

Example 31.2. Creating a stand alone pom.

build.gradle

task writeNewPom << {
    pom {
        project {
            inceptionYear '2008'
            licenses {
                license {
                    name 'The Apache Software License, Version 2.0'
                    url 'http://www.apache.org/licenses/LICENSE-2.0.txt'
                    distribution 'repo'
                }
            }
        }
    }.writeTo("$buildDir/newpom.xml")
}

Amongst other things, Gradle supports the same builder syntax as polyglot Maven. To learn more about the Gradle Maven POM object, see MavenPom. See also: MavenPluginConvention

31.6. Interacting with Maven repositories

31.6.1. Introduction

With Gradle you can deploy to remote Maven repositories or install to your local Maven repository. This includes all Maven metadata manipulation and works also for Maven snapshots. In fact, Gradle's deployment is 100 percent Maven compatible as we use the native Maven Ant tasks under the hood.

Deploying to a Maven repository is only half the fun if you don't have a POM. Fortunately Gradle can generate this POM for you using the dependency information it has.

31.6.2. Deploying to a Maven repository

Let's assume your project produces just the default jar file. Now you want to deploy this jar file to a remote Maven repository.

Example 31.3. Upload of file to remote Maven repository

build.gradle

apply plugin: 'maven'

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://localhost/tmp/myRepo/")
        }
    }
}

That is all. Calling the uploadArchives task will generate the POM and deploys the artifact and the POM to the specified repository.

There is more work to do if you need support for protocols other than file. In this case the native Maven code we delegate to needs additional libraries. Which libraries are needed depends on what protocol you plan to use. The available protocols and the corresponding libraries are listed in Table 31.3, “Protocol jars for Maven deployment” (those libraries have transitive dependencies which have transitive dependencies). [19] For example, to use the ssh protocol you can do:

Example 31.4. Upload of file via SSH

build.gradle

configurations {
    deployerJars
}

repositories {
    mavenCentral()
}

dependencies {
    deployerJars "org.apache.maven.wagon:wagon-ssh:2.2"
}

uploadArchives {
    repositories.mavenDeployer {
        configuration = configurations.deployerJars
        repository(url: "scp://repos.mycompany.com/releases") {
            authentication(userName: "me", password: "myPassword")
        }
    }
}

There are many configuration options for the Maven deployer. The configuration is done via a Groovy builder. All the elements of this tree are Java beans. To configure the simple attributes you pass a map to the bean elements. To add bean elements to its parent, you use a closure. In the example above repository and authentication are such bean elements. Table 31.4, “Configuration elements of the MavenDeployer” lists the available bean elements and a link to the Javadoc of the corresponding class. In the Javadoc you can see the possible attributes you can set for a particular element.

In Maven you can define repositories and optionally snapshot repositories. If no snapshot repository is defined, releases and snapshots are both deployed to the repository element. Otherwise snapshots are deployed to the snapshotRepository element.

Table 31.3. Protocol jars for Maven deployment

Protocol Library
http org.apache.maven.wagon:wagon-http:2.2
ssh org.apache.maven.wagon:wagon-ssh:2.2
ssh-external org.apache.maven.wagon:wagon-ssh-external:2.2
ftp org.apache.maven.wagon:wagon-ftp:2.2
webdav org.apache.maven.wagon:wagon-webdav:1.0-beta-2
file -

31.6.3. Installing to the local repository

The Maven plugin adds an install task to your project. This task depends on all the archives task of the archives configuration. It installs those archives to your local Maven repository. If the default location for the local repository is redefined in a Maven settings.xml, this is considered by this task.

31.6.4. Maven POM generation

When deploying an artifact to a Maven repository, Gradle automatically generates a POM for it. The groupId, artifactId, version and packaging elements used for the POM default to the values shown in the table below. The dependency elements are created from the project's dependency declarations.

Table 31.5. Default Values for Maven POM generation

Maven Element Default Value
groupId project.group
artifactId uploadTask.repositories.mavenDeployer.pom.artifactId (if set) or archiveTask.baseName.
version project.version
packaging archiveTask.extension

Here, uploadTask and archiveTask refer to the tasks used for uploading and generating the archive, respectively (for example uploadArchives and jar). archiveTask.baseName defaults to project.archivesBaseName which in turn defaults to project.name.

When you set the “archiveTask.baseName” property to a value other than the default, you'll also have to set uploadTask.repositories.mavenDeployer.pom.artifactId to the same value. Otherwise, the project at hand may be referenced with the wrong artifact ID from generated POMs for other projects in the same build.

Generated POMs can be found in <buildDir>/poms. They can be further customized via the MavenPom API. For example, you might want the artifact deployed to the Maven repository to have a different version or name than the artifact generated by Gradle. To customize these you can do:

Example 31.5. Customization of pom

build.gradle

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://localhost/tmp/myRepo/")
            pom.version = '1.0Maven'
            pom.artifactId = 'myMavenName'
        }
    }
}

To add additional content to the POM, the pom.project builder can be used. With this builder, any element listed in the Maven POM reference can be added.

Example 31.6. Builder style customization of pom

build.gradle

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://localhost/tmp/myRepo/")
            pom.project {
                licenses {
                    license {
                        name 'The Apache Software License, Version 2.0'
                        url 'http://www.apache.org/licenses/LICENSE-2.0.txt'
                        distribution 'repo'
                    }
                }
            }
        }
    }
}

Note: groupId, artifactId, version, and packaging should always be set directly on the pom object.

Example 31.7. Modifying auto-generated content

build.gradle

def installer = install.repositories.mavenInstaller
def deployer = uploadArchives.repositories.mavenDeployer

[installer, deployer]*.pom*.whenConfigured {pom ->
    pom.dependencies.find {dep -> dep.groupId == 'group3' && dep.artifactId == 'runtime' }.optional = true
}

If you have more than one artifact to publish, things work a little bit differently. See Section 31.6.4.1, “Multiple artifacts per project”.

To customize the settings for the Maven installer (see Section 31.6.3, “Installing to the local repository”), you can do:

Example 31.8. Customization of Maven installer

build.gradle

install {
    repositories.mavenInstaller {
        pom.version = '1.0Maven'
        pom.artifactId = 'myName'
    }
}

31.6.4.1. Multiple artifacts per project

Maven can only deal with one artifact per project. This is reflected in the structure of the Maven POM. We think there are many situations where it makes sense to have more than one artifact per project. In such a case you need to generate multiple POMs. In such a case you have to explicitly declare each artifact you want to publish to a Maven repository. The MavenDeployer and the MavenInstaller both provide an API for this:

Example 31.9. Generation of multiple poms

build.gradle

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://localhost/tmp/myRepo/")
            addFilter('api') {artifact, file ->
                artifact.name == 'api'
            }
            addFilter('service') {artifact, file ->
                artifact.name == 'service'
            }
            pom('api').version = 'mySpecialMavenVersion'
        }
    }
}

You need to declare a filter for each artifact you want to publish. This filter defines a boolean expression for which Gradle artifact it accepts. Each filter has a POM associated with it which you can configure. To learn more about this have a look at PomFilterContainer and its associated classes.

31.6.4.2. Dependency mapping

The Maven plugin configures the default mapping between the Gradle configurations added by the Java and War plugin and the Maven scopes. Most of the time you don't need to touch this and you can safely skip this section. The mapping works like the following. You can map a configuration to one and only one scope. Different configurations can be mapped to one or different scopes. You can also assign a priority to a particular configuration-to-scope mapping. Have a look at Conf2ScopeMappingContainer to learn more. To access the mapping configuration you can say:

Example 31.10. Accessing a mapping configuration

build.gradle

task mappings << {
    println conf2ScopeMappings.mappings
}

Gradle exclude rules are converted to Maven excludes if possible. Such a conversion is possible if in the Gradle exclude rule the group as well as the module name is specified (as Maven needs both in contrast to Ivy). Per-configuration excludes are also included in the Maven POM, if they are convertible.



[19] It is planned for a future release to provide out-of-the-box support for this

Chapter 32. The Signing Plugin

The signing plugin adds the ability to digitally sign built files and artifacts. These digital signatures can then be used to prove who built the artifact the signature is attached to as well as other information such as when the signature was generated.

The signing plugin currently only provides support for generating OpenPGP signatures (which is the signature format required for publication to the Maven Central Repository).

32.1. Usage

To use the Signing plugin, include the following in your build script:

Example 32.1. Using the Signing plugin

build.gradle

apply plugin: 'signing'

32.2. Signatory credentials

In order to create OpenPGP signatures, you will need a key pair (instructions on creating a key pair using the GnuPG tools can be found in the GnuPG HOWTOs). You need to provide the signing plugin with your key information, which means three things:

  • The public key ID (an 8 character hexadecimal string).

  • The absolute path to the secret key ring file containing your private key.

  • The passphrase used to protect your private key.

These items must be supplied as the values of properties signing.keyId, signing.secretKeyRingFile, and signing.password respectively. Given the personal and private nature of these values, a good practice is to store them in the user gradle.properties file (described in Section 11.2, “Gradle properties and system properties”).

signing.keyId=24875D73
signing.password=secret
signing.secretKeyRingFile=/Users/me/.gnupg/secring.gpg
        

If specifying this information (especially signing.password) in the user gradle.properties file is not feasible for your environment, you can source the information however you need to and set the project properties manually.

import org.gradle.plugins.signing.Sign

gradle.taskGraph.whenReady { taskGraph ->
    if (taskGraph.allTasks.any { it instanceof Sign }) {
        // Use Java 6's console to read from the console (no good for
        // a CI environment)
        Console console = System.console()
        console.printf "\n\nWe have to sign some things in this build." +
                       "\n\nPlease enter your signing details.\n\n"

        def id = console.readLine("PGP Key Id: ")
        def file = console.readLine("PGP Secret Key Ring File (absolute path): ")
        def password = console.readPassword("PGP Private Key Password: ")

        allprojects { ext."signing.keyId" = id }
        allprojects { ext."signing.secretKeyRingFile" = file }
        allprojects { ext."signing.password" = password }

        console.printf "\nThanks.\n\n"
    }
}
        

32.2.1. Using OpenPGP subkeys

OpenPGP supports subkeys, which are like the normal keys, except they're bound to a master key pair. One feature of OpenPGP subkeys is that they can be revoked independently of the master keys which makes key management easier. A practical case study of how subkeys can be leveraged in software development can be read on the Debian wiki.

The signing plugin supports OpenPGP subkeys out of the box. Just specify a subkey ID as the value in the signing.keyId property.

32.3. Specifying what to sign

As well as configuring how things are to be signed (i.e. the signatory configuration), you must also specify what is to be signed. The Signing plugin provides a DSL that allows you to specify the tasks and/or configurations that should be signed.

32.3.1. Signing Configurations

It is common to want to sign the artifacts of a configuration. For example, the Java plugin configures a jar to build and this jar artifact is added to the archives configuration. Using the Signing DSL, you can specify that all of the artifacts of this configuration should be signed.

Example 32.2. Signing a configuration

build.gradle

signing {
    sign configurations.archives
}

This will create a task (of type Sign) in your project named “signArchives”, that will build any archives artifacts (if needed) and then generate signatures for them. The signature files will be placed alongside the artifacts being signed.

Example 32.3. Signing a configuration output

Output of gradle signArchives

> gradle signArchives
:compileJava
:processResources
:classes
:jar
:signArchives

BUILD SUCCESSFUL

Total time: 1 secs

32.3.2. Signing Tasks

In some cases the artifact that you need to sign may not be part of a configuration. In this case you can directly sign the task that produces the artifact to sign.

Example 32.4. Signing a task

build.gradle

task stuffZip (type: Zip) {
    baseName = "stuff"
    from "src/stuff"
}

signing {
    sign stuffZip
}

This will create a task (of type Sign) in your project named “signStuffZip”, that will build the input task's archive (if needed) and then sign it. The signature file will be placed alongside the artifact being signed.

Example 32.5. Signing a task output

Output of gradle signStuffZip

> gradle signStuffZip
:stuffZip
:signStuffZip

BUILD SUCCESSFUL

Total time: 1 secs

For a task to be “signable”, it must produce an archive of some type. Tasks that do this are the Tar, Zip, Jar, War and Ear tasks.

32.3.3. Conditional Signing

A common usage pattern is to only sign build artifacts under certain conditions. For example, you may not wish to sign artifacts for non release versions. To achieve this, you can specify that signing is only required under certain conditions.

Example 32.6. Conditional signing

build.gradle

version = '1.0-SNAPSHOT'
ext.isReleaseVersion = !version.endsWith("SNAPSHOT")

signing {
    required { isReleaseVersion && gradle.taskGraph.hasTask("uploadArchives") }
    sign configurations.archives
}

In this example, we only want to require signing if we are building a release version and we are going to publish it. Because we are inspecting the task graph to determine if we are going to be publishing, we must set the signing.required property to a closure to defer the evaluation. See SigningExtension.setRequired(java.lang.Object) for more information.

32.4. Publishing the signatures

When specifying what is to be signed via the Signing DSL, the resultant signature artifacts are automatically added to the signatures and archives dependency configurations. This means that if you want to upload your signatures to your distribution repository along with the artifacts you simply execute the uploadArchives task as normal.

32.5. Signing POM files

When deploying signatures for your artifacts to a Maven repository, you will also want to sign the published POM file. The signing plugin adds a signing.signPom() (see: SigningExtension.signPom(org.gradle.api.artifacts.maven.MavenDeployment, groovy.lang.Closure)) method that can be used in the beforeDeployment() block in your upload task configuration.

Example 32.7. Signing a POM for deployment

build.gradle

uploadArchives {
    repositories {
        mavenDeployer {
            beforeDeployment { MavenDeployment deployment -> signing.signPom(deployment) }
        }
    }
}

When signing is not required and the POM cannot be signed due to insufficient configuration (i.e. no credentials for signing) then the signPom() method will silently do nothing.

Chapter 33. Ivy Publishing (new)

This chapter describes the new incubating Ivy publishing support provided by the “ivy-publish” plugin. Eventually this new publishing support will replace publishing via the Upload task.

If you are looking for documentation on the original Ivy publishing support using the Upload task please see Chapter 30, Publishing artifacts.

This chapter describes how to publish build artifacts in the Apache Ivy format, usually to a repository for consumption by other builds or projects. What is published is one or more artifacts created by the build, and an Ivy module descriptor (normally ivy.xml) that describes the artifacts and the dependencies of the artifacts, if any.

A published Ivy module can be consumed by Gradle (see Chapter 23, Dependency Management) and other tools that understand the Ivy format.

33.1. The “ivy-publish” Plugin

The ability to publish in the Ivy format is provided by the “ivy-publish” plugin.

The “publishing” plugin creates an extension on the project named “publishing” of type PublishingExtension. This extension provides a container of named publications and a container of named repositories. The “ivy-publish” plugin works with IvyPublication publications and IvyArtifactRepository repositories.

Example 33.1. Applying the “ivy-publish” plugin

build.gradle

apply plugin: 'ivy-publish'

Applying the “ivy-publish” plugin does the following:

33.2. Publications

If you are not familiar with project artifacts and configurations, you should read Chapter 30, Publishing artifacts, which introduces these concepts. This chapter also describes “publishing artifacts” using a different mechanism than what is described in this chapter. The publishing functionality described here will eventually supersede that functionality.

Publication objects describe the structure/configuration of a publication to be created. Publications are published to repositories via tasks, and the configuration of the publication object determines exactly what is published. All of the publications of a project are defined in the PublishingExtension.getPublications() container. Each publication has a unique name within the project.

For the “ivy-publish” plugin to have any effect, an IvyPublication must be added to the set of publications. This publication determines which artifacts are actually published as well as the details included in the associated Ivy module descriptor file. A publication can be configured by adding components, customizing artifacts, and by modifying the generated module descriptor file directly.

33.2.1. Publishing a Software Component

The simplest way to publish a Gradle project to an Ivy repository is to specify a SoftwareComponent to publish. The components presently available for publication are:

Table 33.1. Software Components

Name Provided By Artifacts Dependencies
java Java Plugin Generated jar file Dependencies from 'runtime' configuration
web War Plugin Generated war file No dependencies

In the following example, artifacts and runtime dependencies are taken from the `java` component, which is added by the Java Plugin.

Example 33.2. Publishing a Java module to Ivy

build.gradle

publications {
    ivyJava(IvyPublication) {
        from components.java
    }
}

33.2.2. Publishing custom artifacts

It is also possible to explicitly configure artifacts to be included in the publication. Artifacts are commonly supplied as raw files, or as instances of AbstractArchiveTask (e.g. Jar, Zip).

For each custom artifact, it is possible to specify the name, extension, type, classifier and conf values to use for publication. Note that each artifacts must have a unique name/classifier/extension combination.

Configure custom artifacts as follows:

Example 33.3. Publishing additional artifact to Ivy

build.gradle

task sourceJar(type: Jar) {
    from sourceSets.main.java
    classifier "source"
}
publishing {
    publications {
        ivy(IvyPublication) {
            from components.java
            artifact(sourceJar) {
                type "source"
                conf "runtime"
            }
        }
    }
}

See the IvyPublication class in the API documentation for more detailed information on how artifacts can be customized.

33.2.3. Identity values for the published project

The generated Ivy module descriptor file contains an <info> element that identifies the module. The default identity values are derived from the following:

Overriding the default identity values is easy: simply specify the organisation, module or revision attributes when configuring the IvyPublication. The status and branch attributes can be set via the descriptor property (see IvyModuleDescriptorSpec). The descriptor property can also be used to add additional custom elements as children of the <info> element.

Example 33.4. customizing the publication identity

build.gradle

publishing {
    publications {
        ivy(IvyPublication) {
            organisation 'org.gradle.sample'
            module 'project1-sample'
            revision '1.1'
            descriptor.status = 'milestone'
            descriptor.branch = 'testing'
            descriptor.extraInfo 'http://my.namespace', 'myElement', 'Some value'

            from components.java
        }
    }
}

Certain repositories are not able to handle all supported characters. For example, the ':' character cannot be used as an identifier when publishing to a filesystem-backed repository on Windows.

Gradle will handle any valid Unicode character for organisation, module and revision (as well as artifact name, extension and classifier). The only values that are explicitly prohibited are '\', '/' and any ISO control character. The supplied values are validated early during publication.

33.2.4. Modifying the generated module descriptor

At times, the module descriptor file generated from the project information will need to be tweaked before publishing. The “ivy-publish” plugin provides a hook to allow such modification.

Example 33.5. Customizing the module descriptor file

build.gradle

publications {
    ivyCustom(IvyPublication) {
        descriptor.withXml {
            asNode().info[0].appendNode('description',
                                        'A demonstration of ivy descriptor customization')
        }
    }
}

In this example we are simply adding a 'description' element to the generated Ivy dependency descriptor, but this hook allows you to modify any aspect of the generated descriptor. For example, you could replace the version range for a dependency with the actual version used to produce the build.

See IvyModuleDescriptorSpec.withXml(org.gradle.api.Action) in the API documentation for more information.

It is possible to modify virtually any aspect of the created descriptor should you need to. This means that it is also possible to modify the descriptor in such a way that it is no longer a valid Ivy module descriptor, so care must be taken when using this feature.

The identifier (organisation, module, revision) of the published module is an exception; these values cannot be modified in the descriptor using the `withXML` hook.

33.2.5. Publishing multiple modules

Sometimes it's useful to publish multiple modules from your Gradle build, without creating a separate Gradle subproject. An example is publishing a separate API and implementation jar for your library. With Gradle this is simple:

Example 33.6. Publishing multiple modules from a single project

build.gradle

task apiJar(type: Jar) {
    baseName "publishing-api"
    from sourceSets.main.output
    exclude '**/impl/**'
}
publishing {
    publications {
        impl(IvyPublication) {
            organisation 'org.gradle.sample.impl'
            module 'project2-impl'
            revision '2.3'

            from components.java
        }
        api(IvyPublication) {
            organisation 'org.gradle.sample'
            module 'project2-api'
            revision '2'
        }
    }
}

If a project defines multiple publications then Gradle will publish each of these to the defined repositories. Each publication must be given a unique identity as described above.

33.3. Repositories

Publications are published to repositories. The repositories to publish to are defined by the PublishingExtension.getRepositories() container.

Example 33.7. Declaring repositories to publish to

build.gradle

repositories {
    ivy {
        // change to point to your repo, e.g. http://my.org/repo
        url "$buildDir/repo"
    }
}

The DSL used to declare repositories for publishing is the same DSL that is used to declare repositories for dependencies (RepositoryHandler). However, in the context of Ivy publication only the repositories created by the ivy() methods can be used as publication destinations. You cannot publish an IvyPublication to a Maven repository for example.

33.4. Performing a publish

The “ivy-publish” plugin automatically creates a PublishToIvyRepository task for each IvyPublication and IvyArtifactRepository combination in the publishing.publications and publishing.repositories containers respectively.

The created task is named “publish«PUBNAME»PublicationTo«REPONAME»Repository”, which is “publishIvyJavaPublicationToIvyRepository” for this example. This task is of type PublishToIvyRepository.

Example 33.8. Choosing a particular publication to publish

build.gradle

apply plugin: 'java'
apply plugin: 'ivy-publish'

group = 'org.gradle.sample'
version = '1.0'

publishing {
    publications {
        ivyJava(IvyPublication) {
            from components.java
        }
    }
    repositories {
        ivy {
            // change to point to your repo, e.g. http://my.org/repo
            url "$buildDir/repo"
        }
    }
}

Output of gradle publishIvyJavaPublicationToIvyRepository

> gradle publishIvyJavaPublicationToIvyRepository
:generateDescriptorFileForIvyJavaPublication
:compileJava UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:jar
:publishIvyJavaPublicationToIvyRepository

BUILD SUCCESSFUL

Total time: 1 secs

33.4.1. The “publish” lifecycle task

The “publish” plugin (that the “ivy-publish” plugin implicitly applies) adds a lifecycle task that can be used to publish all publications to all applicable repositories named “publish”.

In more concrete terms, executing this task will execute all PublishToIvyRepository tasks in the project. This is usually the most convenient way to perform a publish.

Example 33.9. Publishing all publications via the “publish” lifecycle task

Output of gradle publish

> gradle publish
:generateDescriptorFileForIvyJavaPublication
:compileJava UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:jar
:publishIvyJavaPublicationToIvyRepository
:publish

BUILD SUCCESSFUL

Total time: 1 secs

33.5. Generating the Ivy module descriptor file without publishing

At times it is useful to generate the Ivy module descriptor file (normally ivy.xml) without publishing your module to an Ivy repository. Since descriptor file generation is performed by a separate task, this is very easy to do.

The “ivy-publish” plugin creates one GenerateIvyDescriptor task for each registered IvyPublication, named “generateDescriptorFileFor«PUBNAME»Publication”, which will be “generateDescriptorFileForIvyJavaPublication” for the previous example of the “ivyJava” publication.

You can specify where the generated Ivy file will be located by setting the destination property on the generated task. By default this file is written to “build/publications/«PUBNAME»/ivy.xml”.

Example 33.10. Generating the Ivy module descriptor file

build.gradle

model {
    tasks.generateDescriptorFileForIvyCustomPublication {
        destination = file("$buildDir/generated-ivy.xml")
    }
}

Output of gradle generateDescriptorFileForIvyCustomPublication

> gradle generateDescriptorFileForIvyCustomPublication
:generateDescriptorFileForIvyCustomPublication

BUILD SUCCESSFUL

Total time: 1 secs

The “ivy-publish” plugin leverages some experimental support for late plugin configuration, and the GenerateIvyDescriptor task will not be constructed until the publishing extension is configured. The simplest way to ensure that the publishing plugin is configured when you attempt to access the GenerateIvyDescriptor task is to place the access inside a model block, as the example above demonstrates.

The same applies to any attempt to access publication-specific tasks like PublishToIvyRepository. These tasks should be referenced from within a model block.

33.6. Complete example

The following example demonstrates publishing with a multi-project build. Each project publishes a Java component and a configured additional source artifact. The descriptor file is customized to include the project description for each project.

Example 33.11. Publishing a Java module

build.gradle

subprojects {
    apply plugin: 'java'
    apply plugin: 'ivy-publish'

    version = '1.0'
    group = 'org.gradle.sample'

    repositories {
        mavenCentral()
    }
    task sourceJar(type: Jar) {
        from sourceSets.main.java
        classifier "source"
    }
}

project(":project1") {
    description = "The first project"

    dependencies {
       compile 'junit:junit:4.12', project(':project2')
    }
}

project(":project2") {
    description = "The second project"

    dependencies {
       compile 'commons-collections:commons-collections:3.2.2'
    }
}

subprojects {
    publishing {
        repositories {
            ivy {
                // change to point to your repo, e.g. http://my.org/repo
                url "${rootProject.buildDir}/repo"
            }
        }
        publications {
            ivy(IvyPublication) {
                from components.java
                artifact(sourceJar) {
                    type "source"
                    conf "runtime"
                }
                descriptor.withXml {
                    asNode().info[0].appendNode('description', description)
                }
            }
        }
    }
}

The result is that the following artifacts will be published for each project:

  • The Ivy module descriptor file: “ivy-1.0.xml”.
  • The primary “jar” artifact for the Java component: “project1-1.0.jar”.
  • The source “jar” artifact that has been explicitly configured: “project1-1.0-source.jar”.

When project1 is published, the module descriptor (i.e. the ivy.xml file) that is produced will look like:

Note that «PUBLICATION-TIME-STAMP» in this example Ivy module descriptor will be the timestamp of when the descriptor was generated.

Example 33.12. Example generated ivy.xml

output-ivy.xml

<?xml version="1.0" encoding="UTF-8"?>
<ivy-module version="2.0">
  <info organisation="org.gradle.sample" module="project1" revision="1.0" status="integration" publication="«PUBLICATION-TIME-STAMP»">
    <description>The first project</description>
  </info>
  <configurations>
    <conf name="default" visibility="public" extends="runtime"/>
    <conf name="runtime" visibility="public"/>
  </configurations>
  <publications>
    <artifact name="project1" type="jar" ext="jar" conf="runtime"/>
    <artifact name="project1" type="source" ext="jar" conf="runtime" m:classifier="source" xmlns:m="http://ant.apache.org/ivy/maven"/>
  </publications>
  <dependencies>
    <dependency org="junit" name="junit" rev="4.12" conf="runtime-&gt;default"/>
    <dependency org="org.gradle.sample" name="project2" rev="1.0" conf="runtime-&gt;default"/>
  </dependencies>
</ivy-module>

33.7. Future features

The “ivy-publish” plugin functionality as described above is incomplete, as the feature is still incubating. In upcoming Gradle releases, the functionality will be expanded to include (but not limited to):

  • Convenient customization of module attributes (module, organisation etc.)
  • Convenient customization of dependencies reported in module descriptor.
  • Multiple discrete publications per project

Chapter 34. Maven Publishing (new)

This chapter describes the new incubating Maven publishing support provided by the “maven-publish” plugin. Eventually this new publishing support will replace publishing via the Upload task.

If you are looking for documentation on the original Maven publishing support using the Upload task please see Chapter 30, Publishing artifacts.

This chapter describes how to publish build artifacts to an Apache Maven Repository. A module published to a Maven repository can be consumed by Maven, Gradle (see Chapter 23, Dependency Management) and other tools that understand the Maven repository format.

34.1. The “maven-publish” Plugin

The ability to publish in the Maven format is provided by the “maven-publish” plugin.

The “publishing” plugin creates an extension on the project named “publishing” of type PublishingExtension. This extension provides a container of named publications and a container of named repositories. The “maven-publish” plugin works with MavenPublication publications and MavenArtifactRepository repositories.

Example 34.1. Applying the 'maven-publish' plugin

build.gradle

apply plugin: 'maven-publish'

Applying the “maven-publish” plugin does the following:

34.2. Publications

If you are not familiar with project artifacts and configurations, you should read the Chapter 30, Publishing artifacts that introduces these concepts. This chapter also describes “publishing artifacts” using a different mechanism than what is described in this chapter. The publishing functionality described here will eventually supersede that functionality.

Publication objects describe the structure/configuration of a publication to be created. Publications are published to repositories via tasks, and the configuration of the publication object determines exactly what is published. All of the publications of a project are defined in the PublishingExtension.getPublications() container. Each publication has a unique name within the project.

For the “maven-publish” plugin to have any effect, a MavenPublication must be added to the set of publications. This publication determines which artifacts are actually published as well as the details included in the associated POM file. A publication can be configured by adding components, customizing artifacts, and by modifying the generated POM file directly.

34.2.1. Publishing a Software Component

The simplest way to publish a Gradle project to a Maven repository is to specify a SoftwareComponent to publish. The components presently available for publication are:

Table 34.1. Software Components

Name Provided By Artifacts Dependencies
java Chapter 45, The Java Plugin Generated jar file Dependencies from 'runtime' configuration
web Chapter 47, The War Plugin Generated war file No dependencies

In the following example, artifacts and runtime dependencies are taken from the `java` component, which is added by the Java Plugin.

Example 34.2. Adding a MavenPublication for a Java component

build.gradle

publishing {
    publications {
        mavenJava(MavenPublication) {
            from components.java
        }
    }
}

34.2.2. Publishing custom artifacts

It is also possible to explicitly configure artifacts to be included in the publication. Artifacts are commonly supplied as raw files, or as instances of AbstractArchiveTask (e.g. Jar, Zip).

For each custom artifact, it is possible to specify the extension and classifier values to use for publication. Note that only one of the published artifacts can have an empty classifier, and all other artifacts must have a unique classifier/extension combination.

Configure custom artifacts as follows:

Example 34.3. Adding additional artifact to a MavenPublication

build.gradle

task sourceJar(type: Jar) {
    from sourceSets.main.allJava
}

publishing {
    publications {
        mavenJava(MavenPublication) {
            from components.java

            artifact sourceJar {
                classifier "sources"
            }
        }
    }
}

See the MavenPublication class in the API documentation for more information about how artifacts can be customized.

34.2.3. Identity values in the generated POM

The attributes of the generated POM file will contain identity values derived from the following project properties:

Overriding the default identity values is easy: simply specify the groupId, artifactId or version attributes when configuring the MavenPublication.

Example 34.4. customizing the publication identity

build.gradle

publishing {
    publications {
        maven(MavenPublication) {
            groupId 'org.gradle.sample'
            artifactId 'project1-sample'
            version '1.1'

            from components.java
        }
    }
}

Certain repositories will not be able to handle all supported characters. For example, the ':' character cannot be used as an identifier when publishing to a filesystem-backed repository on Windows.

Maven restricts 'groupId' and 'artifactId' to a limited character set ([A-Za-z0-9_\\-.]+) and Gradle enforces this restriction. For 'version' (as well as artifact 'extension' and 'classifier'), Gradle will handle any valid Unicode character.

The only Unicode values that are explicitly prohibited are '\', '/' and any ISO control character. Supplied values are validated early in publication.

34.2.4. Modifying the generated POM

The generated POM file may need to be tweaked before publishing. The “maven-publish” plugin provides a hook to allow such modification.

Example 34.5. Modifying the POM file

build.gradle

publications {
    mavenCustom(MavenPublication) {
        pom.withXml {
            asNode().appendNode('description',
                                'A demonstration of maven POM customization')
        }
    }
}

In this example we are adding a 'description' element for the generated POM. With this hook, you can modify any aspect of the POM. For example, you could replace the version range for a dependency with the actual version used to produce the build.

See MavenPom.withXml(org.gradle.api.Action) in the API documentation for more information.

It is possible to modify virtually any aspect of the created POM should you need to. This means that it is also possible to modify the POM in such a way that it is no longer a valid Maven Pom, so care must be taken when using this feature.

The identifier (groupId, artifactId, version) of the published module is an exception; these values cannot be modified in the POM using the `withXML` hook.

34.2.5. Publishing multiple modules

Sometimes it's useful to publish multiple modules from your Gradle build, without creating a separate Gradle subproject. An example is publishing a separate API and implementation jar for your library. With Gradle this is simple:

Example 34.6. Publishing multiple modules from a single project

build.gradle

task apiJar(type: Jar) {
    baseName "publishing-api"
    from sourceSets.main.output
    exclude '**/impl/**'
}

publishing {
    publications {
        impl(MavenPublication) {
            groupId 'org.gradle.sample.impl'
            artifactId 'project2-impl'
            version '2.3'

            from components.java
        }
        api(MavenPublication) {
            groupId 'org.gradle.sample'
            artifactId 'project2-api'
            version '2'

            artifact apiJar
        }
    }
}

If a project defines multiple publications then Gradle will publish each of these to the defined repositories. Each publication must be given a unique identity as described above.

34.3. Repositories

Publications are published to repositories. The repositories to publish to are defined by the PublishingExtension.getRepositories() container.

Example 34.7. Declaring repositories to publish to

build.gradle

publishing {
    repositories {
        maven {
            // change to point to your repo, e.g. http://my.org/repo
            url "$buildDir/repo"
        }
    }
}

The DSL used to declare repositories for publication is the same DSL that is used to declare repositories to consume dependencies from, RepositoryHandler. However, in the context of Maven publication only MavenArtifactRepository repositories can be used for publication.

34.4. Performing a publish

The “maven-publish” plugin automatically creates a PublishToMavenRepository task for each MavenPublication and MavenArtifactRepository combination in the publishing.publications and publishing.repositories containers respectively.

The created task is named “publish«PUBNAME»PublicationTo«REPONAME»Repository”.

Example 34.8. Publishing a project to a Maven repository

build.gradle

apply plugin: 'java'
apply plugin: 'maven-publish'

group = 'org.gradle.sample'
version = '1.0'

publishing {
    publications {
        mavenJava(MavenPublication) {
            from components.java
        }
    }
}
publishing {
    repositories {
        maven {
            // change to point to your repo, e.g. http://my.org/repo
            url "$buildDir/repo"
        }
    }
}

Output of gradle publish

> gradle publish
:generatePomFileForMavenJavaPublication
:compileJava
:processResources UP-TO-DATE
:classes
:jar
:publishMavenJavaPublicationToMavenRepository
:publish

BUILD SUCCESSFUL

Total time: 1 secs

In this example, a task named “publishMavenJavaPublicationToMavenRepository” is created, which is of type PublishToMavenRepository. This task is wired into the publish lifecycle task. Executing “gradle publish” builds the POM file and all of the artifacts to be published, and transfers them to the repository.

34.5. Publishing to Maven Local

For integration with a local Maven installation, it is sometimes useful to publish the module into the local .m2 repository. In Maven parlance, this is referred to as 'installing' the module. The “maven-publish” plugin makes this easy to do by automatically creating a PublishToMavenLocal task for each MavenPublication in the publishing.publications container. Each of these tasks is wired into the publishToMavenLocal lifecycle task. You do not need to have `mavenLocal` in your `publishing.repositories` section.

The created task is named “publish«PUBNAME»PublicationToMavenLocal”.

Example 34.9. Publish a project to the Maven local repository

Output of gradle publishToMavenLocal

> gradle publishToMavenLocal
:generatePomFileForMavenJavaPublication
:compileJava
:processResources UP-TO-DATE
:classes
:jar
:publishMavenJavaPublicationToMavenLocal
:publishToMavenLocal

BUILD SUCCESSFUL

Total time: 1 secs

The resulting task in this example is named “publishMavenJavaPublicationToMavenLocal”. This task is wired into the publishToMavenLocal lifecycle task. Executing “gradle publishToMavenLocal” builds the POM file and all of the artifacts to be published, and “installs” them into the local Maven repository.

34.6. Generating the POM file without publishing

At times it is useful to generate a Maven POM file for a module without actually publishing. Since POM generation is performed by a separate task, it is very easy to do so.

The task for generating the POM file is of type GenerateMavenPom, and it is given a name based on the name of the publication: “generatePomFileFor«PUBNAME»Publication”. So in the example below, where the publication is named “mavenCustom”, the task will be named “generatePomFileForMavenCustomPublication”.

Example 34.10. Generate a POM file without publishing

build.gradle

model {
    tasks.generatePomFileForMavenCustomPublication {
        destination = file("$buildDir/generated-pom.xml")
    }
}

Output of gradle generatePomFileForMavenCustomPublication

> gradle generatePomFileForMavenCustomPublication
:generatePomFileForMavenCustomPublication

BUILD SUCCESSFUL

Total time: 1 secs

All details of the publishing model are still considered in POM generation, including components`, custom artifacts, and any modifications made via pom.withXml.

The “maven-publish” plugin leverages some experimental support for late plugin configuration, and any GenerateMavenPom tasks will not be constructed until the publishing extension is configured. The simplest way to ensure that the publishing plugin is configured when you attempt to access the GenerateMavenPom task is to place the access inside a model block, as the example above demonstrates.

The same applies to any attempt to access publication-specific tasks like PublishToMavenRepository. These tasks should be referenced from within a model block.

Chapter 35. The Distribution Plugin

The distribution plugin is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The distribution plugin facilitates building archives that serve as distributions of the project. Distribution archives typically contain the executable application and other supporting files, such as documentation.

35.1. Usage

To use the distribution plugin, include the following in your build script:

Example 35.1. Using the distribution plugin

build.gradle

apply plugin: 'distribution'

The plugin adds an extension named “distributions” of type DistributionContainer to the project. It also creates a single distribution in the distributions container extension named “main”. If your build only produces one distribution you only need to configure this distribution (or use the defaults).

You can run “gradle distZip” to package the main distribution as a ZIP, or “gradle distTar” to create a TAR file. To build both types of archives just run gradle assembleDist. The files will be created at “$buildDir/distributions/$project.name-$project.version.«ext»”.

You can run “gradle installDist” to assemble the uncompressed distribution into “$buildDir/install/main”.

35.2. Tasks

The Distribution plugin adds the following tasks to the project:

Table 35.1. Distribution plugin - tasks

Task name Depends on Type Description
distZip - Zip Creates a ZIP archive of the distribution contents
distTar - Tar Creates a TAR archive of the distribution contents
assembleDist distTar, distZip Task Creates ZIP and TAR archives with the distribution contents
installDist - Sync Assembles the distribution content and installs it on the current machine

For each extra distribution set you add to the project, the distribution plugin adds the following tasks:

Table 35.2. Multiple distributions - tasks

Task name Depends on Type Description
${distribution.name}DistZip - Zip Creates a ZIP archive of the distribution contents
${distribution.name}DistTar - Tar Creates a TAR archive of the distribution contents
assemble${distribution.name.capitalize()}Dist ${distribution.name}DistTar, ${distribution.name}DistZip Task Assembles all distribution archives
install${distribution.name.capitalize()}Dist - Sync Assembles the distribution content and installs it on the current machine

Example 35.2. Adding extra distributions

build.gradle

apply plugin: 'distribution'

version = '1.2'
distributions {
    custom {}
}

This will add following tasks to the project:

  • customDistZip
  • customDistTar
  • assembleCustomDist
  • installCustomDist

Given that the project name is “myproject” and version “1.2”, running “gradle customDistZip” will produce a ZIP file named “myproject-custom-1.2.zip”.

Running “gradle installCustomDist” will install the distribution contents into “$buildDir/install/custom”.

35.3. Distribution contents

All of the files in the “src/$distribution.name/dist” directory will automatically be included in the distribution. You can add additional files by configuring the Distribution object that is part of the container.

Example 35.3. Configuring the main distribution

build.gradle

apply plugin: 'distribution'

distributions {
    main {
        baseName = 'someName'
        contents {
            from { 'src/readme' }
        }
    }
}

apply plugin:'maven'

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://some/repo")
        }
    }
}


In the example above, the content of the “src/readme” directory will be included in the distribution (along with the files in the “src/main/dist” directory which are added by default).

The “baseName” property has also been changed. This will cause the distribution archives to be created with a different name.

35.4. Publishing distributions

The distribution plugin adds the distribution archives as candidate for default publishing artifacts. With the maven plugin applied the distribution zip file will be published when running uploadArchives if no other default artifact is configured

Example 35.4. publish main distribution

build.gradle

apply plugin:'maven'

uploadArchives {
    repositories {
        mavenDeployer {
            repository(url: "file://some/repo")
        }
    }
}

Chapter 36. The Announce Plugin

The Gradle announce plugin allows you to send custom announcements during a build. The following notification systems are supported:

36.1. Usage

To use the announce plugin, apply it to your build script:

Example 36.1. Using the announce plugin

build.gradle

apply plugin: 'announce'

Next, configure your notification service(s) of choice (see table below for which configuration properties are available):

Example 36.2. Configure the announce plugin

build.gradle

announce {  
  username = 'myId'
  password = 'myPassword'
}

Finally, send announcements with the announce method:

Example 36.3. Using the announce plugin

build.gradle

task helloWorld << {  
    println "Hello, world!"
}  

helloWorld.doLast {  
    announce.announce("helloWorld completed!", "twitter")
    announce.announce("helloWorld completed!", "local")
}

The announce method takes two String arguments: The message to be sent, and the notification service to be used. The following table lists supported notification services and their configuration properties.

Table 36.1. Announce Plugin Notification Services

Notification Service Operating System Configuration Properties Further Information
twitter Any username, password
snarl Windows
growl Mac OS X
notify-send Ubuntu Requires the notify-send package to be installed. Use sudo apt-get install libnotify-bin to install it.
local Windows, Mac OS X, Ubuntu Automatically chooses between snarl, growl, and notify-send depending on the current operating system.

36.2. Configuration

See the AnnouncePluginExtension class in the API documentation.

Chapter 37. The Build Announcements Plugin

The build announcements plugin is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The build announcements plugin uses the announce plugin to send local announcements on important events in the build.

37.1. Usage

To use the build announcements plugin, include the following in your build script:

Example 37.1. Using the build announcements plugin

build.gradle

apply plugin: 'build-announcements'

That's it. If you want to tweak where the announcements go, you can configure the announce plugin to change the local announcer.

You can also apply the plugin from an init script:

Example 37.2. Using the build announcements plugin from an init script

init.gradle

rootProject {
    apply plugin: 'build-announcements'
}

Part IV. Extending the build

Chapter 38. Writing Custom Task Classes

Gradle supports two types of task. One such type is the simple task, where you define the task with an action closure. We have seen these in Chapter 14, Build Script Basics. For this type of task, the action closure determines the behaviour of the task. This type of task is good for implementing one-off tasks in your build script.

The other type of task is the enhanced task, where the behaviour is built into the task, and the task provides some properties which you can use to configure the behaviour. We have seen these in Chapter 17, More about Tasks. Most Gradle plugins use enhanced tasks. With enhanced tasks, you don't need to implement the task behaviour as you do with simple tasks. You simply declare the task and configure the task using its properties. In this way, enhanced tasks let you reuse a piece of behaviour in many different places, possibly across different builds.

The behaviour and properties of an enhanced task is defined by the task's class. When you declare an enhanced task, you specify the type, or class of the task.

Implementing your own custom task class in Gradle is easy. You can implement a custom task class in pretty much any language you like, provided it ends up compiled to bytecode. In our examples, we are going to use Groovy as the implementation language, but you could use, for example, Java or Scala. In general, using Groovy is the easiest option, because the Gradle API is designed to work well with Groovy.

38.1. Packaging a task class

There are several places where you can put the source for the task class.

Build script

You can include the task class directly in the build script. This has the benefit that the task class is automatically compiled and included in the classpath of the build script without you having to do anything. However, the task class is not visible outside the build script, and so you cannot reuse the task class outside the build script it is defined in.

buildSrc project

You can put the source for the task class in the rootProjectDir/buildSrc/src/main/groovy directory. Gradle will take care of compiling and testing the task class and making it available on the classpath of the build script. The task class is visible to every build script used by the build. However, it is not visible outside the build, and so you cannot reuse the task class outside the build it is defined in. Using the buildSrc project approach separates the task declaration - that is, what the task should do - from the task implementation - that is, how the task does it.

See Chapter 41, Organizing Build Logic for more details about the buildSrc project.

Standalone project

You can create a separate project for your task class. This project produces and publishes a JAR which you can then use in multiple builds and share with others. Generally, this JAR might include some custom plugins, or bundle several related task classes into a single library. Or some combination of the two.

In our examples, we will start with the task class in the build script, to keep things simple. Then we will look at creating a standalone project.

38.2. Writing a simple task class

To implement a custom task class, you extend DefaultTask.

Example 38.1. Defining a custom task

build.gradle

class GreetingTask extends DefaultTask {
}

This task doesn't do anything useful, so let's add some behaviour. To do so, we add a method to the task and mark it with the TaskAction annotation. Gradle will call the method when the task executes. You don't have to use a method to define the behaviour for the task. You could, for instance, call doFirst() or doLast() with a closure in the task constructor to add behaviour.

Example 38.2. A hello world task

build.gradle

task hello(type: GreetingTask)

class GreetingTask extends DefaultTask {
    @TaskAction
    def greet() {
        println 'hello from GreetingTask'
    }
}

Output of gradle -q hello

> gradle -q hello
hello from GreetingTask

Let's add a property to the task, so we can customize it. Tasks are simply POGOs, and when you declare a task, you can set the properties or call methods on the task object. Here we add a greeting property, and set the value when we declare the greeting task.

Example 38.3. A customizable hello world task

build.gradle

// Use the default greeting
task hello(type: GreetingTask)

// Customize the greeting
task greeting(type: GreetingTask) {
    greeting = 'greetings from GreetingTask'
}

class GreetingTask extends DefaultTask {
    String greeting = 'hello from GreetingTask'

    @TaskAction
    def greet() {
        println greeting
    }
}

Output of gradle -q hello greeting

> gradle -q hello greeting
hello from GreetingTask
greetings from GreetingTask

38.3. A standalone project

Now we will move our task to a standalone project, so we can publish it and share it with others. This project is simply a Groovy project that produces a JAR containing the task class. Here is a simple build script for the project. It applies the Groovy plugin, and adds the Gradle API as a compile-time dependency.

Example 38.4. A build for a custom task

build.gradle

apply plugin: 'groovy'

dependencies {
    compile gradleApi()
    compile localGroovy()
}

Note: The code for this example can be found at samples/customPlugin/plugin in the ‘-all’ distribution of Gradle.


We just follow the convention for where the source for the task class should go.

Example 38.5. A custom task

src/main/groovy/org/gradle/GreetingTask.groovy

package org.gradle

import org.gradle.api.DefaultTask
import org.gradle.api.tasks.TaskAction

class GreetingTask extends DefaultTask {
    String greeting = 'hello from GreetingTask'

    @TaskAction
    def greet() {
        println greeting
    }
}

38.3.1. Using your task class in another project

To use a task class in a build script, you need to add the class to the build script's classpath. To do this, you use a buildscript { } block, as described in Section 41.6, “External dependencies for the build script”. The following example shows how you might do this when the JAR containing the task class has been published to a local repository:

Example 38.6. Using a custom task in another project

build.gradle

buildscript {
    repositories {
        maven {
            url uri('../repo')
        }
    }
    dependencies {
        classpath group: 'org.gradle', name: 'customPlugin',
                  version: '1.0-SNAPSHOT'
    }
}

task greeting(type: org.gradle.GreetingTask) {
    greeting = 'howdy!'
}

38.3.2. Writing tests for your task class

You can use the ProjectBuilder class to create Project instances to use when you test your task class.

Example 38.7. Testing a custom task

src/test/groovy/org/gradle/GreetingTaskTest.groovy

class GreetingTaskTest {
    @Test
    public void canAddTaskToProject() {
        Project project = ProjectBuilder.builder().build()
        def task = project.task('greeting', type: GreetingTask)
        assertTrue(task instanceof GreetingTask)
    }
}

38.4. Incremental tasks

Incremental tasks are an incubating feature.

Since the introduction of the implementation described above (early in the Gradle 1.6 release cycle), discussions within the Gradle community have produced superior ideas for exposing the information about changes to task implementors to what is described below. As such, the API for this feature will almost certainly change in upcoming releases. However, please do experiment with the current implementation and share your experiences with the Gradle community.

The feature incubation process, which is part of the Gradle feature lifecycle (see Appendix C, The Feature Lifecycle), exists for this purpose of ensuring high quality final implementations through incorporation of early user feedback.

With Gradle, it's very simple to implement a task that gets skipped when all of it's inputs and outputs are up to date (see Section 17.9, “Skipping tasks that are up-to-date”). However, there are times when only a few input files have changed since the last execution, and you'd like to avoid reprocessing all of the unchanged inputs. This can be particularly useful for a transformer task, that converts input files to output files on a 1:1 basis.

If you'd like to optimise your build so that only out-of-date inputs are processed, you can do so with an incremental task.

38.4.1. Implementing an incremental task

For a task to process inputs incrementally, that task must contain an incremental task action. This is a task action method that contains a single IncrementalTaskInputs parameter, which indicates to Gradle that the action will process the changed inputs only.

The incremental task action may supply an IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action for processing any input file that is out-of-date, and a IncrementalTaskInputs.removed(org.gradle.api.Action) action that executes for any input file that has been removed since the previous execution.

Example 38.8. Defining an incremental task action

build.gradle

class IncrementalReverseTask extends DefaultTask {
    @InputDirectory
    def File inputDir

    @OutputDirectory
    def File outputDir

    @Input
    def inputProperty

    @TaskAction
    void execute(IncrementalTaskInputs inputs) {
        println inputs.incremental ? "CHANGED inputs considered out of date"
                                   : "ALL inputs considered out of date"
        if (!inputs.incremental)
            project.delete(outputDir.listFiles())

        inputs.outOfDate { change ->
            println "out of date: ${change.file.name}"
            def targetFile = new File(outputDir, change.file.name)
            targetFile.text = change.file.text.reverse()
        }

        inputs.removed { change ->
            println "removed: ${change.file.name}"
            def targetFile = new File(outputDir, change.file.name)
            targetFile.delete()
        }
    }
}

Note: The code for this example can be found at samples/userguide/tasks/incrementalTask in the ‘-all’ distribution of Gradle.


If for some reason the task is not run incremental, e.g. by running with --rerun-tasks, only the outOfDate action is executed, even if there where deleted input files. You should consider handling this case at the beginning, as is done in the example above.

For a simple transformer task like this, the task action simply needs to generate output files for any out-of-date inputs, and delete output files for any removed inputs.

A task may only contain a single incremental task action.

38.4.2. Which inputs are considered out of date?

When Gradle has history of a previous task execution, and the only changes to the task execution context since that execution are to input files, then Gradle is able to determine which input files need to be reprocessed by the task. In this case, the IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action will be executed for any input file that was added or modified, and the IncrementalTaskInputs.removed(org.gradle.api.Action) action will be executed for any removed input file.

However, there are many cases where Gradle is unable to determine which input files need to be reprocessed. Examples include:

  • There is no history available from a previous execution.
  • You are building with a different version of Gradle. Currently, Gradle does not use task history from a different version.
  • An upToDateWhen criteria added to the task returns false.
  • An input property has changed since the previous execution.
  • One or more output files have changed since the previous execution.

In any of these cases, Gradle will consider all of the input files to be outOfDate. The IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action will be executed for every input file, and the IncrementalTaskInputs.removed(org.gradle.api.Action) action will not be executed at all.

You can check if Gradle was able to determine the incremental changes to input files with IncrementalTaskInputs.isIncremental().

38.4.3. An incremental task in action

Given the incremental task implementation above, we can explore the various change scenarios by example. Note that the various mutation tasks ('updateInputs', 'removeInput', etc) are only present for demonstration purposes: these would not normally be part of your build script.

First, consider the IncrementalReverseTask executed against a set of inputs for the first time. In this case, all inputs will be considered “out of date”:

Example 38.9. Running the incremental task for the first time

build.gradle

task incrementalReverse(type: IncrementalReverseTask) {
    inputDir = file('inputs')
    outputDir = file("$buildDir/outputs")
    inputProperty = project.properties['taskInputProperty'] ?: "original"
}

Build layout

incrementalTask/
  build.gradle
  inputs/
    1.txt
    2.txt
    3.txt

Output of gradle -q incrementalReverse

> gradle -q incrementalReverse
ALL inputs considered out of date
out of date: 1.txt
out of date: 2.txt
out of date: 3.txt

Naturally when the task is executed again with no changes, then the entire task is up to date and no files are reported to the task action:

Example 38.10. Running the incremental task with unchanged inputs

Output of gradle -q incrementalReverse

> gradle -q incrementalReverse

When an input file is modified in some way or a new input file is added, then re-executing the task results in those files being reported to IncrementalTaskInputs.outOfDate(org.gradle.api.Action):

Example 38.11. Running the incremental task with updated input files

build.gradle

task updateInputs() << {
    file('inputs/1.txt').text = "Changed content for existing file 1."
    file('inputs/4.txt').text = "Content for new file 4."
}

Output of gradle -q updateInputs incrementalReverse

> gradle -q updateInputs incrementalReverse
CHANGED inputs considered out of date
out of date: 1.txt
out of date: 4.txt

When an existing input file is removed, then re-executing the task results in that file being reported to IncrementalTaskInputs.removed(org.gradle.api.Action):

Example 38.12. Running the incremental task with an input file removed

build.gradle

task removeInput() << {
    file('inputs/3.txt').delete()
}

Output of gradle -q removeInput incrementalReverse

> gradle -q removeInput incrementalReverse
CHANGED inputs considered out of date
removed: 3.txt

When an output file is deleted (or modified), then Gradle is unable to determine which input files are out of date. In this case, all input files are reported to the IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action, and no input files are reported to the IncrementalTaskInputs.removed(org.gradle.api.Action) action:

Example 38.13. Running the incremental task with an output file removed

build.gradle

task removeOutput() << {
    file("$buildDir/outputs/1.txt").delete()
}

Output of gradle -q removeOutput incrementalReverse

> gradle -q removeOutput incrementalReverse
ALL inputs considered out of date
out of date: 1.txt
out of date: 2.txt
out of date: 3.txt

When a task input property is modified, Gradle is unable to determine how this property impacted the task outputs, so all input files are assumed to be out of date. So similar to the changed output file example, all input files are reported to the IncrementalTaskInputs.outOfDate(org.gradle.api.Action) action, and no input files are reported to the IncrementalTaskInputs.removed(org.gradle.api.Action) action:

Example 38.14. Running the incremental task with an input property changed

Output of gradle -q -PtaskInputProperty=changed incrementalReverse

> gradle -q -PtaskInputProperty=changed incrementalReverse
ALL inputs considered out of date
out of date: 1.txt
out of date: 2.txt
out of date: 3.txt

Chapter 39. Writing Custom Plugins

A Gradle plugin packages up reusable pieces of build logic, which can be used across many different projects and builds. Gradle allows you to implement your own custom plugins, so you can reuse your build logic, and share it with others.

You can implement a custom plugin in any language you like, provided the implementation ends up compiled as bytecode. For the examples here, we are going to use Groovy as the implementation language. You could use Java or Scala instead, if you want.

39.1. Packaging a plugin

There are several places where you can put the source for the plugin.

Build script

You can include the source for the plugin directly in the build script. This has the benefit that the plugin is automatically compiled and included in the classpath of the build script without you having to do anything. However, the plugin is not visible outside the build script, and so you cannot reuse the plugin outside the build script it is defined in.

buildSrc project

You can put the source for the plugin in the rootProjectDir/buildSrc/src/main/groovy directory. Gradle will take care of compiling and testing the plugin and making it available on the classpath of the build script. The plugin is visible to every build script used by the build. However, it is not visible outside the build, and so you cannot reuse the plugin outside the build it is defined in.

See Chapter 41, Organizing Build Logic for more details about the buildSrc project.

Standalone project

You can create a separate project for your plugin. This project produces and publishes a JAR which you can then use in multiple builds and share with others. Generally, this JAR might include some custom plugins, or bundle several related task classes into a single library. Or some combination of the two.

In our examples, we will start with the plugin in the build script, to keep things simple. Then we will look at creating a standalone project.

39.2. Writing a simple plugin

To create a custom plugin, you need to write an implementation of Plugin. Gradle instantiates the plugin and calls the plugin instance's Plugin.apply(T) method when the plugin is used with a project. The project object is passed as a parameter, which the plugin can use to configure the project however it needs to. The following sample contains a greeting plugin, which adds a hello task to the project.

Example 39.1. A custom plugin

build.gradle

apply plugin: GreetingPlugin

class GreetingPlugin implements Plugin<Project> {
    void apply(Project project) {
        project.task('hello') << {
            println "Hello from the GreetingPlugin"
        }
    }
}

Output of gradle -q hello

> gradle -q hello
Hello from the GreetingPlugin

One thing to note is that a new instance of a given plugin is created for each project it is applied to. Also note that the Plugin class is a generic type. This example has it receiving the Project type as a type parameter. It's possible to write unusual custom plugins that take different type parameters, but this will be unlikely (until someone figures out more creative things to do here).

39.3. Getting input from the build

Most plugins need to obtain some configuration from the build script. One method for doing this is to use extension objects. The Gradle Project has an associated ExtensionContainer object that helps keep track of all the settings and properties being passed to plugins. You can capture user input by telling the extension container about your plugin. To capture input, simply add a Java Bean compliant class into the extension container's list of extensions. Groovy is a good language choice for a plugin because plain old Groovy objects contain all the getter and setter methods that a Java Bean requires.

Let's add a simple extension object to the project. Here we add a greeting extension object to the project, which allows you to configure the greeting.

Example 39.2. A custom plugin extension

build.gradle

apply plugin: GreetingPlugin

greeting.message = 'Hi from Gradle'

class GreetingPlugin implements Plugin<Project> {
    void apply(Project project) {
        // Add the 'greeting' extension object
        project.extensions.create("greeting", GreetingPluginExtension)
        // Add a task that uses the configuration
        project.task('hello') << {
            println project.greeting.message
        }
    }
}

class GreetingPluginExtension {
    def String message = 'Hello from GreetingPlugin'
}

Output of gradle -q hello

> gradle -q hello
Hi from Gradle

In this example, GreetingPluginExtension is a plain old Groovy object with a field called message. The extension object is added to the plugin list with the name greeting. This object then becomes available as a project property with the same name as the extension object.

Oftentimes, you have several related properties you need to specify on a single plugin. Gradle adds a configuration closure block for each extension object, so you can group settings together. The following example shows you how this works.

Example 39.3. A custom plugin with configuration closure

build.gradle

apply plugin: GreetingPlugin

greeting {
    message = 'Hi'
    greeter = 'Gradle'
}

class GreetingPlugin implements Plugin<Project> {
    void apply(Project project) {
        project.extensions.create("greeting", GreetingPluginExtension)
        project.task('hello') << {
            println "${project.greeting.message} from ${project.greeting.greeter}"
        }
    }
}

class GreetingPluginExtension {
    String message
    String greeter
}

Output of gradle -q hello

> gradle -q hello
Hi from Gradle

In this example, several settings can be grouped together within the greeting closure. The name of the closure block in the build script (greeting) needs to match the extension object name. Then, when the closure is executed, the fields on the extension object will be mapped to the variables within the closure based on the standard Groovy closure delegate feature.

39.4. Working with files in custom tasks and plugins

When developing custom tasks and plugins, it's a good idea to be very flexible when accepting input configuration for file locations. To do this, you can leverage the Project.file(java.lang.Object) method to resolve values to files as late as possible.

Example 39.4. Evaluating file properties lazily

build.gradle

class GreetingToFileTask extends DefaultTask {

    def destination

    File getDestination() {
        project.file(destination)
    }

    @TaskAction
    def greet() {
        def file = getDestination()
        file.parentFile.mkdirs()
        file.write "Hello!"
    }
}

task greet(type: GreetingToFileTask) {
    destination = { project.greetingFile }
}

task sayGreeting(dependsOn: greet) << {
    println file(greetingFile).text
}

ext.greetingFile = "$buildDir/hello.txt"

Output of gradle -q sayGreeting

> gradle -q sayGreeting
Hello!

In this example, we configure the greet task destination property as a closure, which is evaluated with the Project.file(java.lang.Object) method to turn the return value of the closure into a file object at the last minute. You will notice that in the example above we specify the greetingFile property value after we have configured to use it for the task. This kind of lazy evaluation is a key benefit of accepting any value when setting a file property, then resolving that value when reading the property.

39.5. A standalone project

Now we will move our plugin to a standalone project, so we can publish it and share it with others. This project is simply a Groovy project that produces a JAR containing the plugin classes. Here is a simple build script for the project. It applies the Groovy plugin, and adds the Gradle API as a compile-time dependency.

Example 39.5. A build for a custom plugin

build.gradle

apply plugin: 'groovy'

dependencies {
    compile gradleApi()
    compile localGroovy()
}

Note: The code for this example can be found at samples/customPlugin/plugin in the ‘-all’ distribution of Gradle.


So how does Gradle find the Plugin implementation? The answer is you need to provide a properties file in the jar's META-INF/gradle-plugins directory that matches the id of your plugin.

Example 39.6. Wiring for a custom plugin

src/main/resources/META-INF/gradle-plugins/org.samples.greeting.properties

implementation-class=org.gradle.GreetingPlugin

Notice that the properties filename matches the plugin id and is placed in the resources folder, and that the implementation-class property identifies the Plugin implementation class.

39.5.1. Creating a plugin id

Plugin ids are fully qualified in a manner similar to Java packages (i.e. a reverse domain name). This helps to avoid collisions and provides a way to group plugins with similar ownership.

Your plugin id should be a combination of components that reflect namespace (a reasonable pointer to you or your organization) and the name of the plugin it provides. For example if you had a Github account named “foo” and your plugin was named “bar”, a suitable plugin id might be com.github.foo.bar. Similarly, if the plugin was developed at the baz organization, the plugin id might be org.baz.bar.

Plugin ids should conform to the following:

  • May contain any alphanumeric character, '.', and '-'.
  • Must contain at least one '.' character separating the namespace from the name of the plugin.
  • Conventionally use a lowercase reverse domain name convention for the namespace.
  • Conventionally use only lowercase characters in the name.
  • org.gradle and com.gradleware namespaces may not be used.
  • Cannot start or end with a '.' character.
  • Cannot contain consecutive '.' characters (i.e. '..').

Although there are conventional similarities between plugin ids and package names, package names are generally more detailed than is necessary for a plugin id. For instance, it might seem reasonable to add “gradle” as a component of your plugin id, but since plugin ids are only used for Gradle plugins, this would be superfluous. Generally, a namespace that identifies ownership and a name are all that are needed for a good plugin id.

39.5.2. Publishing your plugin

If you are publishing your plugin internally for use within your organization, you can publish it like any other code artifact. See the ivy and maven chapters on publishing artifacts.

If you are interested in publishing your plugin to be used by the wider Gradle community, you can publish it to the Gradle plugin portal. This site provides the ability to search for and gather information about plugins contributed by the Gradle community. See the instructions here on how to make your plugin available on this site.

39.5.3. Using your plugin in another project

To use a plugin in a build script, you need to add the plugin classes to the build script's classpath. To do this, you use a “buildscript { }” block, as described in Section 25.4, “Applying plugins with the buildscript block”. The following example shows how you might do this when the JAR containing the plugin has been published to a local repository:

Example 39.7. Using a custom plugin in another project

build.gradle

buildscript {
    repositories {
        maven {
            url uri('../repo')
        }
    }
    dependencies {
        classpath group: 'org.gradle', name: 'customPlugin',
                  version: '1.0-SNAPSHOT'
    }
}
apply plugin: 'org.samples.greeting'

Alternatively, if your plugin is published to the plugin portal, you can use the incubating plugins DSL (see Section 25.5, “Applying plugins with the plugins DSL”) to apply the plugin:

Example 39.8. Applying a community plugin with the plugins DSL

build.gradle

plugins {
    id "com.jfrog.bintray" version "0.4.1"
}

39.5.4. Writing tests for your plugin

You can use the ProjectBuilder class to create Project instances to use when you test your plugin implementation.

Example 39.9. Testing a custom plugin

src/test/groovy/org/gradle/GreetingPluginTest.groovy

class GreetingPluginTest {
    @Test
    public void greeterPluginAddsGreetingTaskToProject() {
        Project project = ProjectBuilder.builder().build()
        project.pluginManager.apply 'org.samples.greeting'

        assertTrue(project.tasks.hello instanceof GreetingTask)
    }
}

39.5.5. Using the Java Gradle Plugin development plugin

You can use the incubating Java Gradle Plugin development plugin to eliminate some of the boilerplate declarations in your build script and provide some basic validations of plugin metadata. This plugin will automatically apply the Java plugin, add the gradleApi() dependency to the compile configuration, and perform plugin metadata validations as part of the jar task execution.

Example 39.10. Using the Java Gradle Plugin Development plugin

build.gradle

plugins {
    id "java-gradle-plugin"
}

When publishing plugins to custom plugin repositories using the ivy or maven publish plugins, the Java Gradle Plugin development plugin will also generate plugin marker artifacts named based on the plugin id which depend on the plugin's implementation artifact.

39.6. Maintaining multiple domain objects

Gradle provides some utility classes for maintaining collections of objects, which work well with the Gradle build language.

Example 39.11. Managing domain objects

build.gradle

apply plugin: DocumentationPlugin

books {
    quickStart {
        sourceFile = file('src/docs/quick-start')
    }
    userGuide {

    }
    developerGuide {

    }
}

task books << {
    books.each { book ->
        println "$book.name -> $book.sourceFile"
    }
}

class DocumentationPlugin implements Plugin<Project> {
    void apply(Project project) {
        def books = project.container(Book)
        books.all {
            sourceFile = project.file("src/docs/$name")
        }
        project.extensions.books = books
    }
}

class Book {
    final String name
    File sourceFile

    Book(String name) {
        this.name = name
    }
}

Output of gradle -q books

> gradle -q books
developerGuide -> /home/user/gradle/samples/userguide/organizeBuildLogic/customPluginWithDomainObjectContainer/src/docs/developerGuide
quickStart -> /home/user/gradle/samples/userguide/organizeBuildLogic/customPluginWithDomainObjectContainer/src/docs/quick-start
userGuide -> /home/user/gradle/samples/userguide/organizeBuildLogic/customPluginWithDomainObjectContainer/src/docs/userGuide

The Project.container(java.lang.Class) methods create instances of NamedDomainObjectContainer, that have many useful methods for managing and configuring the objects. In order to use a type with any of the project.container methods, it MUST expose a property named “name” as the unique, and constant, name for the object. The project.container(Class) variant of the container method creates new instances by attempting to invoke the constructor of the class that takes a single string argument, which is the desired name of the object. See the above link for project.container method variants that allow custom instantiation strategies.

Chapter 40. The Java Gradle Plugin Development Plugin

The Java Gradle plugin development plugin is currently incubating. Please be aware that the DSL and other configuration may change in later Gradle versions.

The Java Gradle Plugin development plugin can be used to assist in the development of Gradle plugins. It automatically applies the Java plugin, adds the gradleApi() dependency to the compile configuration and performs validation of plugin metadata during jar task execution.

The plugin also integrates with TestKit, a library that aids in writing and executing functional tests for plugin code. It automatically adds the gradleTestKit() dependency to the test compile configuration and generates a plugin classpath manifest file consumed by a GradleRunner instance if found. Please refer to Section 43.2.1.2, “Automatic injection with the Java Gradle Plugin Development plugin” for more on its usage, configuration options and samples.

40.1. Usage

To use the Java Gradle Plugin Development plugin, include the following in your build script:

Example 40.1. Using the Java Gradle Plugin Development plugin

build.gradle

plugins {
    id "java-gradle-plugin"
}

Applying the plugin automatically applies the Java plugin and adds the gradleApi() dependency to the compile configuration. It also decorates the jar task with validations.

The following validations are performed:

  • There is a plugin descriptor defined for the plugin.
  • The plugin descriptor contains an implementation-class property.
  • The implementation-class property references a valid class file in the jar.

Any failed validations will result in a warning message.

For each plugin you are developing, add an entry to the gradlePlugin {} script block:

Example 40.2. Using the gradlePlugin {} block.

build.gradle

gradlePlugin {
    plugins {
        simplePlugin {
            id = "org.gradle.sample.simple-plugin"
            implementationClass = "org.gradle.sample.SimplePlugin"
        }
    }
}

The gradlePlugin {} block defines the plugins being built by the project including the id and implementationClass of the plugin. From this data about the plugins being developed, Gradle can automatically:

  • Generate the plugin descriptor in the jar file's META-INF directory.
  • Configure the Maven or Ivy publishing plugins to publish a Plugin Marker Artifact for each plugin.

Chapter 41. Organizing Build Logic

Gradle offers a variety of ways to organize your build logic. First of all you can put your build logic directly in the action closure of a task. If a couple of tasks share the same logic you can extract this logic into a method. If multiple projects of a multi-project build share some logic you can define this method in the parent project. If the build logic gets too complex for being properly modeled by methods then you likely should implement your logic with classes to encapsulate your logic. [20] Gradle makes this very easy. Just drop your classes in a certain directory and Gradle automatically compiles them and puts them in the classpath of your build script.

Here is a summary of the ways you can organise your build logic:

  • POGOs. You can declare and use plain old Groovy objects (POGOs) directly in your build script. The build script is written in Groovy, after all, and Groovy provides you with lots of excellent ways to organize code.

  • Inherited properties and methods. In a multi-project build, sub-projects inherit the properties and methods of their parent project.

  • Configuration injection. In a multi-project build, a project (usually the root project) can inject properties and methods into another project.

  • buildSrc project. Drop the source for your build classes into a certain directory and Gradle automatically compiles them and includes them in the classpath of your build script.

  • Shared scripts. Define common configuration in an external build, and apply the script to multiple projects, possibly across different builds.

  • Custom tasks. Put your build logic into a custom task, and reuse that task in multiple places.

  • Custom plugins. Put your build logic into a custom plugin, and apply that plugin to multiple projects. The plugin must be in the classpath of your build script. You can achieve this either by using build sources or by adding an external library that contains the plugin.

  • Execute an external build. Execute another Gradle build from the current build.

  • External libraries. Use external libraries directly in your build file.

41.1. Inherited properties and methods

Any method or property defined in a project build script is also visible to all the sub-projects. You can use this to define common configurations, and to extract build logic into methods which can be reused by the sub-projects.

Example 41.1. Using inherited properties and methods

build.gradle

// Define an extra property
ext.srcDirName = 'src/java'

// Define a method
def getSrcDir(project) {
    return project.file(srcDirName)
}

child/build.gradle

task show << {
    // Use inherited property
    println 'srcDirName: ' + srcDirName

    // Use inherited method
    File srcDir = getSrcDir(project)
    println 'srcDir: ' + rootProject.relativePath(srcDir)
}

Output of gradle -q show

> gradle -q show
srcDirName: src/java
srcDir: child/src/java

41.2. Injected configuration

You can use the configuration injection technique discussed in Section 24.1, “Cross project configuration” and Section 24.2, “Subproject configuration” to inject properties and methods into various projects. This is generally a better option than inheritance, for a number of reasons: The injection is explicit in the build script, You can inject different logic into different projects, And you can inject any kind of configuration such as repositories, plug-ins, tasks, and so on. The following sample shows how this works.

Example 41.2. Using injected properties and methods

build.gradle

subprojects {
    // Define a new property
    ext.srcDirName = 'src/java'

    // Define a method using a closure as the method body
    ext.srcDir = { file(srcDirName) }

    // Define a task
    task show << {
        println 'project: ' + project.path
        println 'srcDirName: ' + srcDirName
        File srcDir = srcDir()
        println 'srcDir: ' + rootProject.relativePath(srcDir)
    }
}

// Inject special case configuration into a particular project
project(':child2') {
    ext.srcDirName = "$srcDirName/legacy"
}

child1/build.gradle

// Use injected property and method. Here, we override the injected value
srcDirName = 'java'
def dir = srcDir()

Output of gradle -q show

> gradle -q show
project: :child1
srcDirName: java
srcDir: child1/java
project: :child2
srcDirName: src/java/legacy
srcDir: child2/src/java/legacy

41.3. Configuring the project using an external build script

You can configure the current project using an external build script. All of the Gradle build language is available in the external script. You can even apply other scripts from the external script.

Example 41.3. Configuring the project using an external build script

build.gradle

apply from: 'other.gradle'

other.gradle

println "configuring $project"
task hello << {
    println 'hello from other script'
}

Output of gradle -q hello

> gradle -q hello
configuring root project 'configureProjectUsingScript'
hello from other script

41.4. Build sources in the buildSrc project

When you run Gradle, it checks for the existence of a directory called buildSrc. Gradle then automatically compiles and tests this code and puts it in the classpath of your build script. You don't need to provide any further instruction. This can be a good place to add your custom tasks and plugins.

For multi-project builds there can be only one buildSrc directory, which has to be in the root project directory.

Listed below is the default build script that Gradle applies to the buildSrc project:

Figure 41.1. Default buildSrc build script

apply plugin: 'groovy'
dependencies {
    compile gradleApi()
    compile localGroovy()
}


This means that you can just put your build source code in this directory and stick to the layout convention for a Java/Groovy project (see Table 45.4, “Java plugin - default project layout”).

If you need more flexibility, you can provide your own build.gradle. Gradle applies the default build script regardless of whether there is one specified. This means you only need to declare the extra things you need. Below is an example. Notice that this example does not need to declare a dependency on the Gradle API, as this is done by the default build script:

Example 41.4. Custom buildSrc build script

buildSrc/build.gradle

repositories {
    mavenCentral()
}

dependencies {
    testCompile 'junit:junit:4.12'
}

The buildSrc project can be a multi-project build, just like any other regular multi-project build. However, all of the projects that should be on the classpath of the actual build must be runtime dependencies of the root project in buildSrc. You can do this by adding this to the configuration of each project you wish to export:

Example 41.5. Adding subprojects to the root buildSrc project

buildSrc/build.gradle

rootProject.dependencies {
  runtime project(path)
}

Note: The code for this example can be found at samples/multiProjectBuildSrc in the ‘-all’ distribution of Gradle.


41.5. Running another Gradle build from a build

You can use the GradleBuild task. You can use either of the dir or buildFile properties to specify which build to execute, and the tasks property to specify which tasks to execute.

Example 41.6. Running another build from a build

build.gradle

task build(type: GradleBuild) {
    buildFile = 'other.gradle'
    tasks = ['hello']
}

other.gradle

task hello << {
    println "hello from the other build."
}

Output of gradle -q build

> gradle -q build
hello from the other build.

41.6. External dependencies for the build script

If your build script needs to use external libraries, you can add them to the script's classpath in the build script itself. You do this using the buildscript() method, passing in a closure which declares the build script classpath.

Example 41.7. Declaring external dependencies for the build script

build.gradle

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'commons-codec', name: 'commons-codec', version: '1.2'
    }
}

The closure passed to the buildscript() method configures a ScriptHandler instance. You declare the build script classpath by adding dependencies to the classpath configuration. This is the same way you declare, for example, the Java compilation classpath. You can use any of the dependency types described in Section 23.4, “How to declare your dependencies”, except project dependencies.

Having declared the build script classpath, you can use the classes in your build script as you would any other classes on the classpath. The following example adds to the previous example, and uses classes from the build script classpath.

Example 41.8. A build script with external dependencies

build.gradle

import org.apache.commons.codec.binary.Base64

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'commons-codec', name: 'commons-codec', version: '1.2'
    }
}

task encode << {
    def byte[] encodedString = new Base64().encode('hello world\n'.getBytes())
    println new String(encodedString)
}

Output of gradle -q encode

> gradle -q encode
aGVsbG8gd29ybGQK

For multi-project builds, the dependencies declared with a project's buildscript() method are available to the build scripts of all its sub-projects.

Build script dependencies may be Gradle plugins. Please consult Chapter 25, Gradle Plugins for more information on Gradle plugins.

Every project automatically has a buildEnvironment task of type BuildEnvironmentReportTask that can be invoked to report on the resolution of the build script dependencies.

41.7. Ant optional dependencies

For reasons we don't fully understand yet, external dependencies are not picked up by Ant's optional tasks. But you can easily do it in another way. [21]

Example 41.9. Ant optional dependencies

build.gradle

configurations {
    ftpAntTask
}

dependencies {
    ftpAntTask("org.apache.ant:ant-commons-net:1.9.6") {
        module("commons-net:commons-net:1.4.1") {
            dependencies "oro:oro:2.0.8:jar"
        }
    }
}

task ftp << {
    ant {
        taskdef(name: 'ftp',
                classname: 'org.apache.tools.ant.taskdefs.optional.net.FTP',
                classpath: configurations.ftpAntTask.asPath)
        ftp(server: "ftp.apache.org", userid: "anonymous", password: "me@myorg.com") {
            fileset(dir: "htdocs/manual")
        }
    }
}

This is also a good example for the usage of client modules. The POM file in Maven Central for the ant-commons-net task does not provide the right information for this use case.

41.8. Summary

Gradle offers you a variety of ways of organizing your build logic. You can choose what is right for your domain and find the right balance between unnecessary indirections, and avoiding redundancy and a hard to maintain code base. It is our experience that even very complex custom build logic is rarely shared between different builds. Other build tools enforce a separation of this build logic into a separate project. Gradle spares you this unnecessary overhead and indirection.



[20] Which might range from a single class to something very complex.

[21] In fact, we think this is a better solution. Only if your buildscript and Ant's optional task need the same library would you have to define it twice. In such a case it would be nice if Ant's optional task would automatically pick up the classpath defined in the “gradle.settings” file.

Chapter 42. Initialization Scripts

Gradle provides a powerful mechanism to allow customizing the build based on the current environment. This mechanism also supports tools that wish to integrate with Gradle.

Note that this is completely different from the “init” task provided by the “build-init” incubating plugin (see Chapter 15, Build Init Plugin).

42.1. Basic usage

Initialization scripts (a.k.a. init scripts) are similar to other scripts in Gradle. These scripts, however, are run before the build starts. Here are several possible uses:

  • Set up enterprise-wide configuration, such as where to find custom plugins.

  • Set up properties based on the current environment, such as a developer's machine vs. a continuous integration server.

  • Supply personal information about the user that is required by the build, such as repository or database authentication credentials.

  • Define machine specific details, such as where JDKs are installed.

  • Register build listeners. External tools that wish to listen to Gradle events might find this useful.

  • Register build loggers. You might wish to customize how Gradle logs the events that it generates.

One main limitation of init scripts is that they cannot access classes in the buildSrc project (see Section 41.4, “Build sources in the buildSrc project” for details of this feature).

42.2. Using an init script

There are several ways to use an init script:

  • Specify a file on the command line. The command line option is -I or --init-script followed by the path to the script. The command line option can appear more than once, each time adding another init script.

  • Put a file called init.gradle in the USER_HOME/.gradle/ directory.

  • Put a file that ends with .gradle in the USER_HOME/.gradle/init.d/ directory.

  • Put a file that ends with .gradle in the GRADLE_HOME/init.d/ directory, in the Gradle distribution. This allows you to package up a custom Gradle distribution containing some custom build logic and plugins. You can combine this with the Gradle wrapper as a way to make custom logic available to all builds in your enterprise.

If more than one init script is found they will all be executed, in the order specified above. Scripts in a given directory are executed in alphabetical order. This allows, for example, a tool to specify an init script on the command line and the user to put one in their home directory for defining the environment and both scripts will run when Gradle is executed.

42.3. Writing an init script

Similar to a Gradle build script, an init script is a Groovy script. Each init script has a Gradle instance associated with it. Any property reference and method call in the init script will delegate to this Gradle instance.

Each init script also implements the Script interface.

42.3.1. Configuring projects from an init script

You can use an init script to configure the projects in the build. This works in a similar way to configuring projects in a multi-project build. The following sample shows how to perform extra configuration from an init script before the projects are evaluated. This sample uses this feature to configure an extra repository to be used only for certain environments.

Example 42.1. Using init script to perform extra configuration before projects are evaluated

build.gradle

repositories {
    mavenCentral()
}

task showRepos << {
    println "All repos:"
    println repositories.collect { it.name }
}

init.gradle

allprojects {
    repositories {
        mavenLocal()
    }
}

Output of gradle --init-script init.gradle -q showRepos

> gradle --init-script init.gradle -q showRepos
All repos:
[MavenLocal, MavenRepo]

42.4. External dependencies for the init script

In Section 41.6, “External dependencies for the build script” it was explained how to add external dependencies to a build script. Init scripts can also declare dependencies. You do this with the initscript() method, passing in a closure which declares the init script classpath.

Example 42.2. Declaring external dependencies for an init script

init.gradle

initscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'org.apache.commons', name: 'commons-math', version: '2.0'
    }
}

The closure passed to the initscript() method configures a ScriptHandler instance. You declare the init script classpath by adding dependencies to the classpath configuration. This is the same way you declare, for example, the Java compilation classpath. You can use any of the dependency types described in Section 23.4, “How to declare your dependencies”, except project dependencies.

Having declared the init script classpath, you can use the classes in your init script as you would any other classes on the classpath. The following example adds to the previous example, and uses classes from the init script classpath.

Example 42.3. An init script with external dependencies

init.gradle

import org.apache.commons.math.fraction.Fraction

initscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'org.apache.commons', name: 'commons-math', version: '2.0'
    }
}

println Fraction.ONE_FIFTH.multiply(2)

Output of gradle --init-script init.gradle -q doNothing

> gradle --init-script init.gradle -q doNothing
2 / 5

42.5. Init script plugins

Similar to a Gradle build script or a Gradle settings file, plugins can be applied on init scripts.

Example 42.4. Using plugins in init scripts

init.gradle

apply plugin:EnterpriseRepositoryPlugin

class EnterpriseRepositoryPlugin implements Plugin<Gradle> {

    private static String ENTERPRISE_REPOSITORY_URL = "https://repo.gradle.org/gradle/repo"

    void apply(Gradle gradle) {
        // ONLY USE ENTERPRISE REPO FOR DEPENDENCIES
        gradle.allprojects{ project ->
            project.repositories {

                // Remove all repositories not pointing to the enterprise repository url
                all { ArtifactRepository repo ->
                    if (!(repo instanceof MavenArtifactRepository) ||
                          repo.url.toString() != ENTERPRISE_REPOSITORY_URL) {
                        project.logger.lifecycle "Repository ${repo.url} removed. Only $ENTERPRISE_REPOSITORY_URL is allowed"
                        remove repo
                    }
                }

                // add the enterprise repository
                maven {
                    name "STANDARD_ENTERPRISE_REPO"
                    url ENTERPRISE_REPOSITORY_URL
                }
            }
        }
    }
}

build.gradle

repositories{
    mavenCentral()
}

 task showRepositories << {
    repositories.each{
        println "repository: ${it.name} ('${it.url}')"
    }
}

Output of gradle -q -I init.gradle showRepositories

> gradle -q -I init.gradle showRepositories
repository: STANDARD_ENTERPRISE_REPO ('https://repo.gradle.org/gradle/repo')

The plugin in the init script ensures that only a specified repository is used when running the build.

When applying plugins within the init script, Gradle instantiates the plugin and calls the plugin instance's Plugin.apply(T) method. The gradle object is passed as a parameter, which can be used to configure all aspects of a build. Of course, the applied plugin can be resolved as an external dependency as described in Section 42.4, “External dependencies for the init script”

Chapter 43. The Gradle TestKit

The Gradle TestKit is currently incubating. Please be aware that its API and other characteristics may change in later Gradle versions.

The Gradle TestKit (a.k.a. just TestKit) is a library that aids in testing Gradle plugins and build logic generally. At this time, it is focused on functional testing. That is, testing build logic by exercising it as part of a programmatically executed build. Over time, the TestKit will likely expand to facilitate other kinds of tests.

43.1. Usage

To use the TestKit, include the following in your plugin's build:

Example 43.1. Declaring the TestKit dependency

build.gradle

dependencies {
    testCompile gradleTestKit()
}

The gradleTestKit() encompasses the classes of the TestKit, as well as the Gradle Tooling API client. It does not include a version of JUnit, TestNG, or any other test execution framework. Such a dependency must be explicitly declared.

Example 43.2. Declaring the JUnit dependency

build.gradle

dependencies {
    testCompile 'junit:junit:4.12'
}

43.2. Functional testing with the Gradle runner

The GradleRunner facilitates programmatically executing Gradle builds, and inspecting the result.

A contrived build can be created (e.g. programmatically, or from a template) that exercises the “logic under test”. The build can then be executed, potentially in a variety of ways (e.g. different combinations of tasks and arguments). The correctness of the logic can then be verified by asserting the following, potentially in combination:

  • The build's output;
  • The build's logging (i.e. console output);
  • The set of tasks executed by the build and their results (e.g. FAILED, UP-TO-DATE etc.).

After creating and configuring a runner instance, the build can be executed via the GradleRunner.build() or GradleRunner.buildAndFail() methods depending on the anticipated outcome.

The following demonstrates the usage of Gradle runner in a Java JUnit test:

Example 43.3. Using GradleRunner with JUnit

BuildLogicFunctionalTest.java

import org.gradle.testkit.runner.BuildResult;
import org.gradle.testkit.runner.GradleRunner;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Collections;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

import static org.gradle.testkit.runner.TaskOutcome.*;

public class BuildLogicFunctionalTest {
    @Rule public final TemporaryFolder testProjectDir = new TemporaryFolder();
    private File buildFile;

    @Before
    public void setup() throws IOException {
        buildFile = testProjectDir.newFile("build.gradle");
    }

    @Test
    public void testHelloWorldTask() throws IOException {
        String buildFileContent = "task helloWorld {" +
                                  "    doLast {" +
                                  "        println 'Hello world!'" +
                                  "    }" +
                                  "}";
        writeFile(buildFile, buildFileContent);

        BuildResult result = GradleRunner.create()
            .withProjectDir(testProjectDir.getRoot())
            .withArguments("helloWorld")
            .build();

        assertTrue(result.getOutput().contains("Hello world!"));
        assertEquals(result.task(":helloWorld").getOutcome(), SUCCESS);
    }

    private void writeFile(File destination, String content) throws IOException {
        BufferedWriter output = null;
        try {
            output = new BufferedWriter(new FileWriter(destination));
            output.write(content);
        } finally {
            if (output != null) {
                output.close();
            }
        }
    }
}

Any test execution framework can be used.

As Gradle build scripts are written in the Groovy programming language, and as many plugins are implemented in Groovy, it is often a productive choice to write Gradle functional tests in Groovy. Furthermore, it is recommended to use the (Groovy based) Spock test execution framework as it offers many compelling features over the use of JUnit.

The following demonstrates the usage of Gradle runner in a Groovy Spock test:

Example 43.4. Using GradleRunner with Spock

BuildLogicFunctionalTest.groovy

import org.gradle.testkit.runner.GradleRunner
import static org.gradle.testkit.runner.TaskOutcome.*
import org.junit.Rule
import org.junit.rules.TemporaryFolder
import spock.lang.Specification

class BuildLogicFunctionalTest extends Specification {
    @Rule final TemporaryFolder testProjectDir = new TemporaryFolder()
    File buildFile

    def setup() {
        buildFile = testProjectDir.newFile('build.gradle')
    }

    def "hello world task prints hello world"() {
        given:
        buildFile << """
            task helloWorld {
                doLast {
                    println 'Hello world!'
                }
            }
        """

        when:
        def result = GradleRunner.create()
            .withProjectDir(testProjectDir.root)
            .withArguments('helloWorld')
            .build()

        then:
        result.output.contains('Hello world!')
        result.task(":helloWorld").outcome == SUCCESS
    }
}

It is a common practice to implement any custom build logic (like plugins and task types) that is more complex in nature as external classes in a standalone project. The main driver behind this approach is bundle the compiled code into a JAR file, publish it to a binary repository and reuse it across various projects.

43.2.1. Getting the plugin-under-test into the test build

The GradleRunner uses the Tooling API to execute builds. An implication of this is that the builds are executed in a separate process (i.e. not the same process executing the tests). Therefore, the test build does not share the same classpath or classloaders as the test process and the code under test is not implicitly available to the test build.

Starting with version 2.13, Gradle provides a conventional mechanism to inject the code under test into the test build.

For earlier versions of Gradle (before 2.13), it is possible to manually make the code under test available via some extra configuration. The following example demonstrates having the build generate a file containing the implementation classpath of the code under test, and making it available at test runtime.

Example 43.5. Making the code under test classpath available to the tests

build.gradle

// Write the plugin's classpath to a file to share with the tests
task createClasspathManifest {
    def outputDir = file("$buildDir/$name")

    inputs.files sourceSets.main.runtimeClasspath
    outputs.dir outputDir

    doLast {
        outputDir.mkdirs()
        file("$outputDir/plugin-classpath.txt").text = sourceSets.main.runtimeClasspath.join("\n")
    }
}

// Add the classpath file to the test runtime classpath
dependencies {
    testRuntime files(createClasspathManifest)
}

Note: The code for this example can be found at samples/testKit/gradleRunner/manualClasspathInjection in the ‘-all’ distribution of Gradle.


The tests can then read this value, and inject the classpath into the test build by using the method GradleRunner.withPluginClasspath(java.lang.Iterable). This classpath is then available to use to locate plugins in a test build via the plugins DSL (see Chapter 25, Gradle Plugins). Applying plugins with the plugins DSL requires the definition of a plugin identifier. The following is an example (in Groovy) of doing this from within a Spock Framework setup() method, which is analogous to a JUnit @Before method.

This approach works well when executing the functional tests as part of the Gradle build. When executing the functional tests from an IDE, there are extra considerations. Namely, the classpath manifest file points to the class files etc. generated by Gradle and not the IDE. This means that after making a change to the source of the code under test, the source must be recompiled by Gradle. Similarly, if the effective classpath of the code under test changes, the manifest must be regenerated. In either case, executing the testClasses task of the build will ensure that things are up to date.

43.2.1.1. Working with Gradle versions prior to 2.8

The GradleRunner.withPluginClasspath(java.lang.Iterable) method will not work when executing the build with a Gradle version earlier than 2.8 (see: Section 43.2.3, “The Gradle version used to test”), as this feature is not supported on such Gradle versions.

Instead, the code must be injected via the build script itself. The following sample demonstrates how this can be done.

Example 43.6. Injecting the code under test classes into test builds

src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy

List<File> pluginClasspath

def setup() {
    buildFile = testProjectDir.newFile('build.gradle')

    def pluginClasspathResource = getClass().classLoader.findResource("plugin-classpath.txt")
    if (pluginClasspathResource == null) {
        throw new IllegalStateException("Did not find plugin classpath resource, run `testClasses` build task.")
    }

    pluginClasspath = pluginClasspathResource.readLines().collect { new File(it) }
}

def "hello world task prints hello world"() {
    given:
    buildFile << """
        plugins {
            id 'org.gradle.sample.helloworld'
        }
    """

    when:
    def result = GradleRunner.create()
        .withProjectDir(testProjectDir.root)
        .withArguments('helloWorld')
        .withPluginClasspath(pluginClasspath)
        .build()

    then:
    result.output.contains('Hello world!')
    result.task(":helloWorld").outcome == SUCCESS
}

Note: The code for this example can be found at samples/testKit/gradleRunner/manualClasspathInjection in the ‘-all’ distribution of Gradle.

src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy

List<File> pluginClasspath

def setup() {
    buildFile = testProjectDir.newFile('build.gradle')

    def pluginClasspathResource = getClass().classLoader.findResource("plugin-classpath.txt")
    if (pluginClasspathResource == null) {
        throw new IllegalStateException("Did not find plugin classpath resource, run `testClasses` build task.")
    }

    pluginClasspath = pluginClasspathResource.readLines().collect { new File(it) }
}

def "hello world task prints hello world with pre Gradle 2.8"() {
    given:
    def classpathString = pluginClasspath
        .collect { it.absolutePath.replace('\\', '\\\\') } // escape backslashes in Windows paths
        .collect { "'$it'" }
        .join(", ")

    buildFile << """
        buildscript {
            dependencies {
                classpath files($classpathString)
            }
        }
        apply plugin: "org.gradle.sample.helloworld"
    """

    when:
    def result = GradleRunner.create()
        .withProjectDir(testProjectDir.root)
        .withArguments('helloWorld')
        .withGradleVersion("2.7")
        .build()

    then:
    result.output.contains('Hello world!')
    result.task(":helloWorld").outcome == SUCCESS
}

Note: The code for this example can be found at samples/testKit/gradleRunner/manualClasspathInjection in the ‘-all’ distribution of Gradle.


43.2.1.2. Automatic injection with the Java Gradle Plugin Development plugin

The Java Gradle Plugin development plugin can be used to assist in the development of Gradle plugins. Starting with Gradle version 2.13, the plugin provides a direct integration with TestKit. When applied to a project, the plugin automatically adds the gradleTestKit() dependency to the test compile configuration. Furthermore, it automatically generates the classpath for the code under test and injects it via GradleRunner.withPluginClasspath() for any GradleRunner instance created by the user. If the target Gradle version is prior to 2.8, automatic plugin classpath injection is not performed.

The plugin uses the following conventions for applying the TestKit dependency and injecting the classpath:

  • Source set containing code under test: sourceSets.main
  • Source set used for injecting the plugin classpath: sourceSets.test

Any of these conventions can be reconfigured with the help of the class GradlePluginDevelopmentExtension.

The following Groovy-based sample demonstrates how to automatically inject the plugin classpath by using the standard conventions applied by the Java Gradle Plugin Development plugin.

Example 43.7. Using the Java Gradle Development plugin for generating the plugin metadata

build.gradle

apply plugin: 'groovy'
apply plugin: 'java-gradle-plugin'

dependencies {
    testCompile('org.spockframework:spock-core:1.0-groovy-2.4') {
        exclude module: 'groovy-all'
    }
}

Note: The code for this example can be found at samples/testKit/gradleRunner/automaticClasspathInjectionQuickstart in the ‘-all’ distribution of Gradle.


Example 43.8. Automatically injecting the code under test classes into test builds

src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy

def "hello world task prints hello world"() {
    given:
    buildFile << """
        plugins {
            id 'org.gradle.sample.helloworld'
        }
    """

    when:
    def result = GradleRunner.create()
        .withProjectDir(testProjectDir.root)
        .withArguments('helloWorld')
        .withPluginClasspath()
        .build()

    then:
    result.output.contains('Hello world!')
    result.task(":helloWorld").outcome == SUCCESS
}

Note: The code for this example can be found at samples/testKit/gradleRunner/automaticClasspathInjectionQuickstart in the ‘-all’ distribution of Gradle.


The following build script demonstrates how to reconfigure the conventions provided by the Java Gradle Plugin Development plugin for a project that uses a custom Test source set.

Example 43.9. Reconfiguring the classpath generation conventions of the Java Gradle Development plugin

build.gradle

apply plugin: 'groovy'
apply plugin: 'java-gradle-plugin'

sourceSets {
    functionalTest {
        groovy {
            srcDir file('src/functionalTest/groovy')
        }
        resources {
            srcDir file('src/functionalTest/resources')
        }
        compileClasspath += sourceSets.main.output + configurations.testRuntime
        runtimeClasspath += output + compileClasspath
    }
}

task functionalTest(type: Test) {
    testClassesDir = sourceSets.functionalTest.output.classesDir
    classpath = sourceSets.functionalTest.runtimeClasspath
}

check.dependsOn functionalTest

gradlePlugin {
    testSourceSets sourceSets.functionalTest
}

dependencies {
    functionalTestCompile('org.spockframework:spock-core:1.0-groovy-2.4') {
        exclude module: 'groovy-all'
    }
}

Note: The code for this example can be found at samples/testKit/gradleRunner/automaticClasspathInjectionCustomTestSourceSet in the ‘-all’ distribution of Gradle.


43.2.2. Controlling the build environment

The runner executes the test builds in an isolated environment by specifying a dedicated "working directory" in a directory inside the JVM's temp directory (i.e. the location specified by the java.io.tmpdir system property, typically /tmp). Any configuration in the default Gradle user home directory (e.g. ~/.gradle/gradle.properties) is not used for test execution. The TestKit does not expose a mechanism for fine grained control of environment variables etc. Future versions of the TestKit will provide improved configuration options.

The TestKit uses dedicated daemon processes that are automatically shut down after test execution.

43.2.3. The Gradle version used to test

The Gradle runner requires a Gradle distribution in order to execute the build. The TestKit does not depend on all of Gradle's implementation.

By default, the runner will attempt to find a Gradle distribution based on where the GradleRunner class was loaded from. That is, it is expected that the class was loaded from a Gradle distribution, as is the case when using the gradleTestKit() dependency declaration.

When using the runner as part of tests being executed by Gradle (e.g. executing the test task of a plugin project), the same distribution used to execute the tests will be used by the runner. When using the runner as part of tests being executed by an IDE, the same distribution of Gradle that was used when importing the project will be used. This means that the plugin will effectively be tested with the same version of Gradle that it is being built with.

Alternatively, a different and specific version of Gradle to use can be specified by the any of the following GradleRunner methods:

This can potentially be used to test build logic across Gradle versions. The following demonstrates a cross-version compatibility test written as Groovy Spock test:

Example 43.10. Specifying a Gradle version for test execution

BuildLogicFunctionalTest.groovy

import org.gradle.testkit.runner.GradleRunner
import static org.gradle.testkit.runner.TaskOutcome.*
import org.junit.Rule
import org.junit.rules.TemporaryFolder
import spock.lang.Specification
import spock.lang.Unroll

class BuildLogicFunctionalTest extends Specification {
    @Rule final TemporaryFolder testProjectDir = new TemporaryFolder()
    File buildFile

    def setup() {
        buildFile = testProjectDir.newFile('build.gradle')
    }

    @Unroll
    def "can execute hello world task with Gradle version #gradleVersion"() {
        given:
        buildFile << """
            task helloWorld {
                doLast {
                    logger.quiet 'Hello world!'
                }
            }
        """

        when:
        def result = GradleRunner.create()
            .withGradleVersion(gradleVersion)
            .withProjectDir(testProjectDir.root)
            .withArguments('helloWorld')
            .build()

        then:
        result.output.contains('Hello world!')
        result.task(":helloWorld").outcome == SUCCESS

        where:
        gradleVersion << ['2.6', '2.7']
    }
}

43.2.3.1. Feature support when testing with different Gradle versions

It is possible to use the GradleRunner to execute builds with Gradle 1.0 and later. However, some runner features are not supported on earlier versions. In such cases, the runner will throw an exception when attempting to use the feature.

The following table lists the features that are sensitive to the Gradle version being used.

Table 43.1. Gradle version compatibility

Feature Minimum Version Description
Inspecting executed tasks 2.5 Inspecting the executed tasks, using BuildResult.getTasks() and similar methods.
Plugin classpath injection 2.8 Injecting the code under test via GradleRunner.withPluginClasspath(java.lang.Iterable).
Inspecting build output in debug mode 2.9 Inspecting the build's text output when run in debug mode, using BuildResult.getOutput().
Automatic plugin classpath injection 2.13 Injecting the code under test automatically via GradleRunner.withPluginClasspath() by applying the Java Gradle Plugin Development plugin.

43.2.4. Debugging build logic

The runner uses the Tooling API to execute builds. An implication of this is that the builds are executed in a separate process (i.e. not the same process executing the tests). Therefore, executing your tests in debug mode does not allow you to debug your build logic as you may expect. Any breakpoints set in your IDE will be not be tripped by the code being exercised by the test build.

The TestKit provides two different ways to enable the debug mode:

  • Setting “org.gradle.testkit.debug” system property to true for the JVM using the GradleRunner (i.e. not the build being executed with the runner);
  • Calling the GradleRunner.withDebug(boolean) method.

The system property approach can be used when it is desirable to enable debugging support without making an adhoc change to the runner configuration. Most IDEs offer the capability to set JVM system properties for test execution, and such a feature can be used to set this system property.

Part V. Building JVM projects

Chapter 44. Java Quickstart

44.1. The Java plugin

As we have seen, Gradle is a general-purpose build tool. It can build pretty much anything you care to implement in your build script. Out-of-the-box, however, it doesn't build anything unless you add code to your build script to do so.

Most Java projects are pretty similar as far as the basics go: you need to compile your Java source files, run some unit tests, and create a JAR file containing your classes. It would be nice if you didn't have to code all this up for every project. Luckily, you don't have to. Gradle solves this problem through the use of plugins. A plugin is an extension to Gradle which configures your project in some way, typically by adding some pre-configured tasks which together do something useful. Gradle ships with a number of plugins, and you can easily write your own and share them with others. One such plugin is the Java plugin. This plugin adds some tasks to your project which will compile and unit test your Java source code, and bundle it into a JAR file.

The Java plugin is convention based. This means that the plugin defines default values for many aspects of the project, such as where the Java source files are located. If you follow the convention in your project, you generally don't need to do much in your build script to get a useful build. Gradle allows you to customize your project if you don't want to or cannot follow the convention in some way. In fact, because support for Java projects is implemented as a plugin, you don't have to use the plugin at all to build a Java project, if you don't want to.

We have in-depth coverage with many examples about the Java plugin, dependency management and multi-project builds in later chapters. In this chapter we want to give you an initial idea of how to use the Java plugin to build a Java project.

44.2. A basic Java project

Let's look at a simple example. To use the Java plugin, add the following to your build file:

Example 44.1. Using the Java plugin

build.gradle

apply plugin: 'java'

Note: The code for this example can be found at samples/java/quickstart in the ‘-all’ distribution of Gradle.


This is all you need to define a Java project. This will apply the Java plugin to your project, which adds a number of tasks to your project.

What tasks are available?

You can use gradle tasks to list the tasks of a project. This will let you see the tasks that the Java plugin has added to your project.

Gradle expects to find your production source code under src/main/java and your test source code under src/test/java. In addition, any files under src/main/resources will be included in the JAR file as resources, and any files under src/test/resources will be included in the classpath used to run the tests. All output files are created under the build directory, with the JAR file ending up in the build/libs directory.

44.2.1. Building the project

The Java plugin adds quite a few tasks to your project. However, there are only a handful of tasks that you will need to use to build the project. The most commonly used task is the build task, which does a full build of the project. When you run gradle build, Gradle will compile and test your code, and create a JAR file containing your main classes and resources:

Example 44.2. Building a Java project

Output of gradle build

> gradle build
:compileJava
:processResources
:classes
:jar
:assemble
:compileTestJava
:processTestResources
:testClasses
:test
:check
:build

BUILD SUCCESSFUL

Total time: 1 secs

Some other useful tasks are:

clean

Deletes the build directory, removing all built files.

assemble

Compiles and jars your code, but does not run the unit tests. Other plugins add more artifacts to this task. For example, if you use the War plugin, this task will also build the WAR file for your project.

check

Compiles and tests your code. Other plugins add more checks to this task. For example, if you use the checkstyle plugin, this task will also run Checkstyle against your source code.

44.2.2. External dependencies

Usually, a Java project will have some dependencies on external JAR files. To reference these JAR files in the project, you need to tell Gradle where to find them. In Gradle, artifacts such as JAR files, are located in a repository. A repository can be used for fetching the dependencies of a project, or for publishing the artifacts of a project, or both. For this example, we will use the public Maven repository:

Example 44.3. Adding Maven repository

build.gradle

repositories {
    mavenCentral()
}

Let's add some dependencies. Here, we will declare that our production classes have a compile-time dependency on commons collections, and that our test classes have a compile-time dependency on junit:

Example 44.4. Adding dependencies

build.gradle

dependencies {
    compile group: 'commons-collections', name: 'commons-collections', version: '3.2.2'
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

You can find out more in Chapter 7, Dependency Management Basics.

44.2.3. Customizing the project

The Java plugin adds a number of properties to your project. These properties have default values which are usually sufficient to get started. It's easy to change these values if they don't suit. Let's look at this for our sample. Here we will specify the version number for our Java project, along with the Java version our source is written in. We also add some attributes to the JAR manifest.

Example 44.5. Customization of MANIFEST.MF

build.gradle

sourceCompatibility = 1.5
version = '1.0'
jar {
    manifest {
        attributes 'Implementation-Title': 'Gradle Quickstart',
                   'Implementation-Version': version
    }
}

What properties are available?

You can use gradle properties to list the properties of a project. This will allow you to see the properties added by the Java plugin, and their default values.

The tasks which the Java plugin adds are regular tasks, exactly the same as if they were declared in the build file. This means you can use any of the mechanisms shown in earlier chapters to customize these tasks. For example, you can set the properties of a task, add behaviour to a task, change the dependencies of a task, or replace a task entirely. In our sample, we will configure the test task, which is of type Test, to add a system property when the tests are executed:

Example 44.6. Adding a test system property

build.gradle

test {
    systemProperties 'property': 'value'
}

44.2.4. Publishing the JAR file

Usually the JAR file needs to be published somewhere. To do this, you need to tell Gradle where to publish the JAR file. In Gradle, artifacts such as JAR files are published to repositories. In our sample, we will publish to a local directory. You can also publish to a remote location, or multiple locations.

Example 44.7. Publishing the JAR file

build.gradle

uploadArchives {
    repositories {
       flatDir {
           dirs 'repos'
       }
    }
}

To publish the JAR file, run gradle uploadArchives.

44.2.5. Creating an Eclipse project

To create the Eclipse-specific descriptor files, like .project, you need to add another plugin to your build file:

Example 44.8. Eclipse plugin

build.gradle

apply plugin: 'eclipse'

Now execute gradle eclipse command to generate Eclipse project files. More information about the eclipse task can be found in Chapter 65, The Eclipse Plugins.

44.2.6. Summary

Here's the complete build file for our sample:

Example 44.9. Java example - complete build file

build.gradle

apply plugin: 'java'
apply plugin: 'eclipse'

sourceCompatibility = 1.5
version = '1.0'
jar {
    manifest {
        attributes 'Implementation-Title': 'Gradle Quickstart',
                   'Implementation-Version': version
    }
}

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'commons-collections', name: 'commons-collections', version: '3.2.2'
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

test {
    systemProperties 'property': 'value'
}

uploadArchives {
    repositories {
       flatDir {
           dirs 'repos'
       }
    }
}

44.3. Multi-project Java build

Now let's look at a typical multi-project build. Below is the layout for the project:

Example 44.10. Multi-project build - hierarchical layout

Build layout

multiproject/
  api/
  services/webservice/
  shared/
  services/shared/

Note: The code for this example can be found at samples/java/multiproject in the ‘-all’ distribution of Gradle.


Here we have four projects. Project api produces a JAR file which is shipped to the client to provide them a Java client for your XML webservice. Project webservice is a webapp which returns XML. Project shared contains code used both by api and webservice. Project services/shared has code that depends on the shared project.

44.3.1. Defining a multi-project build

To define a multi-project build, you need to create a settings file. The settings file lives in the root directory of the source tree, and specifies which projects to include in the build. It must be called settings.gradle. For this example, we are using a simple hierarchical layout. Here is the corresponding settings file:

Example 44.11. Multi-project build - settings.gradle file

settings.gradle

include "shared", "api", "services:webservice", "services:shared"

You can find out more about the settings file in Chapter 24, Multi-project Builds.

44.3.2. Common configuration

For most multi-project builds, there is some configuration which is common to all projects. In our sample, we will define this common configuration in the root project, using a technique called configuration injection. Here, the root project is like a container and the subprojects method iterates over the elements of this container - the projects in this instance - and injects the specified configuration. This way we can easily define the manifest content for all archives, and some common dependencies:

Example 44.12. Multi-project build - common configuration

build.gradle

subprojects {
    apply plugin: 'java'
    apply plugin: 'eclipse-wtp'

    repositories {
       mavenCentral()
    }

    dependencies {
        testCompile 'junit:junit:4.12'
    }

    version = '1.0'

    jar {
        manifest.attributes provider: 'gradle'
    }
}

Notice that our sample applies the Java plugin to each subproject. This means the tasks and configuration properties we have seen in the previous section are available in each subproject. So, you can compile, test, and JAR all the projects by running gradle build from the root project directory.

Also note that these plugins are only applied within the subprojects section, not at the root level, so the root build will not expect to find Java source files in the root project, only in the subprojects.

44.3.3. Dependencies between projects

You can add dependencies between projects in the same build, so that, for example, the JAR file of one project is used to compile another project. In the api build file we will add a dependency on the shared project. Due to this dependency, Gradle will ensure that project shared always gets built before project api.

Example 44.13. Multi-project build - dependencies between projects

api/build.gradle

dependencies {
    compile project(':shared')
}

See Section 24.7.1, “Disabling the build of dependency projects” for how to disable this functionality.

44.3.4. Creating a distribution

We also add a distribution, that gets shipped to the client:

Example 44.14. Multi-project build - distribution file

api/build.gradle

task dist(type: Zip) {
    dependsOn spiJar
    from 'src/dist'
    into('libs') {
        from spiJar.archivePath
        from configurations.runtime
    }
}

artifacts {
   archives dist
}

44.4. Where to next?

In this chapter, you have seen how to do some of the things you commonly need to build a Java based project. This chapter is not exhaustive, and there are many other things you can do with Java projects in Gradle. You can find out more about the Java plugin in Chapter 45, The Java Plugin, and you can find more sample Java projects in the samples/java directory in the Gradle distribution.

Otherwise, continue on to Chapter 7, Dependency Management Basics.

Chapter 45. The Java Plugin

The Java plugin adds Java compilation along with testing and bundling capabilities to a project. It serves as the basis for many of the other Gradle plugins.

45.1. Usage

To use the Java plugin, include the following in your build script:

Example 45.1. Using the Java plugin

build.gradle

apply plugin: 'java'

45.2. Source sets

The Java plugin introduces the concept of a source set. A source set is simply a group of source files which are compiled and executed together. These source files may include Java source files and resource files. Other plugins add the ability to include Groovy and Scala source files in a source set. A source set has an associated compile classpath, and runtime classpath.

One use for source sets is to group source files into logical groups which describe their purpose. For example, you might use a source set to define an integration test suite, or you might use separate source sets to define the API and implementation classes of your project.

The Java plugin defines two standard source sets, called main and test. The main source set contains your production source code, which is compiled and assembled into a JAR file. The test source set contains your test source code, which is compiled and executed using JUnit or TestNG. These can be unit tests, integration tests, acceptance tests, or any combination that is useful to you.

45.3.&nb