Chapter 24. The Groovy Plugin

The Groovy plugin extends the Java plugin to add support for Groovy projects. It can deal with Groovy code, mixed Groovy and Java code, and even pure Java code (although we don't necessarily recommend to use it for the latter). The plugin supports joint compilation, which allows to freely mix and match Groovy and Java code, with dependencies in both directions. For example, a Groovy class can extend a Java class that in turn extends a Groovy class. This makes it possible to use the best language for the job, and to rewrite any class in the other language if needed.

24.1. Usage

To use the Groovy plugin, include in your build script:

Example 24.1. Using the Groovy plugin


apply plugin: 'groovy'

24.2. Tasks

The Groovy plugin adds the following tasks to the project.

Table 24.1. Groovy plugin - tasks

Task name Depends on Type Description
compileGroovy compileJava GroovyCompile Compiles production Groovy source files.
compileTestGroovy compileTestJava GroovyCompile Compiles test Groovy source files.
compileSourceSetGroovy compileSourceSetJava GroovyCompile Compiles the given source set's Groovy source files.
groovydoc - Groovydoc Generates API documentation for the production Groovy source files.

The Groovy plugin adds the following dependencies to tasks added by the Java plugin.

Table 24.2. Groovy plugin - additional task dependencies

Task nameDepends on
classes compileGroovy
testClasses compileTestGroovy
sourceSetClasses compileSourceSetGroovy

Figure 24.1. Groovy plugin - tasks

Groovy plugin - tasks

24.3. Project layout

The Groovy plugin assumes the project layout shown in Table 24.3, “Groovy plugin - project layout”. All the Groovy source directories can contain Groovy and Java code. The Java source directories may only contain Java source code. [9] None of these directories need to exist or have anything in them; the Groovy plugin will simply compile whatever it finds.

Table 24.3. Groovy plugin - project layout

Directory Meaning
src/main/java Production Java source
src/main/resources Production resources
src/main/groovy Production Groovy sources. May also contain Java sources for joint compilation.
src/test/java Test Java source
src/test/resources Test resources
src/test/groovy Test Groovy sources. May also contain Java sources for joint compilation.
src/sourceSet/java Java source for the given source set
src/sourceSet/resources Resources for the given source set
src/sourceSet/groovy Groovy sources for the given source set. May also contain Java sources for joint compilation.

24.3.1. Changing the project layout

Just like the Java plugin, the Groovy plugin allows to configure custom locations for Groovy production and test sources.

Example 24.2. Custom Groovy source layout


sourceSets {
    main {
        groovy {
            srcDirs = ['src/groovy']

    test {
        groovy {
            srcDirs = ['test/groovy']

24.4. Dependency management

Because Gradle itself is partly implemented in Groovy, and its build language is also based on Groovy, Gradle already ships with a Groovy library (1.8.6 as of Gradle 1.3). Nevertheless, Groovy projects need to explicitly add a Groovy dependency to the appropriate configuration(s). This dependency, which can be the same or a different Groovy version than the one used internally by Gradle, will then be used as a compile and runtime dependency for the project's Groovy code. It will also be used to execute the Groovy compiler and Groovydoc tool, respectively. [10]

If Groovy is used both for production code, the Groovy dependency should be added to the compile configuration:

Example 24.3. Configuration of Groovy dependency


repositories {

dependencies {
    compile 'org.codehaus.groovy:groovy-all:2.0.5'

If Groovy is only used for test code, the Groovy dependency should be added to the testCompile (but not the compile) configuration:

Example 24.4. Configuration of Groovy test dependency


dependencies {
    testCompile "org.codehaus.groovy:groovy-all:2.0.5"

To use the same Groovy library that ships with Gradle, declare a localGroovy() dependency. Note that different Gradle versions ship with different Groovy versions; as such, using localGroovy() is less safe then explicitly choosing a Groovy version.

Example 24.5. Configuration of bundled Groovy dependency


dependencies {
    compile localGroovy()

In earlier Gradle versions, the Groovy dependency was instead added to the groovy configuration. This is no longer the preferred approach, but is still supported for backwards compatibility.

Example 24.6. Configuration of Groovy configuration


dependencies {
    groovy "org.codehaus.groovy:groovy-all:2.0.5"

The Groovy library doesn't necessarily have to come from a remote repository. It could also come from a local lib directory, perhaps checked in to source control:

Example 24.7. Configuration of Groovy file dependency


repositories {
    flatDir { dirs 'lib' }

dependencies {
    groovy module(':groovy:1.6.0') {
        module(':ant:1.7.0') {
            dependencies(':ant-junit:1.7.0:jar', ':ant-launcher:1.7.0')

24.5. Adding custom GroovyCompile and Groovydoc tasks

When adding custom GroovyCompile and Groovydoc tasks, it's important to understand that these tasks consume Groovy in two ways: on their classpath, and on their groovyClasspath. The former is the regular class path required by these tools to locate referenced classes, and will typically contain more than just the Groovy library. The latter is used to load the Groovy compiler and Groovydoc tool, respectively, and shouldn't contain anything other than the Groovy library and its dependencies.

Unless groovyClasspath is explicitly configured for a task, the Groovy (base) plugin will try to infer the Groovy library to be used from the task'sclasspath. For example, if classpath contains groovy-all-2.0.5.jar, the plugin will add the same dependency to groovyClasspath. If the project has at least one repository defined, an external dependency will be added (e.g. "org.codehaus.groovy:groovy-all:2.0.5"); otherwise, a file dependency will be added.

Note: When using the groovy rather than the groovy-all artifact, automatic configuration of groovyClasspath will only work correctly if the project declares a repository that contains the groovy artifact along with a descriptor (pom.xml or ivy.xml) listing its dependencies. Otherwise, only the artifact itself will be added to groovyClasspath, which will likely result in a NoClassDefFoundError during compilation.

24.6. Convention properties

The Groovy plugin does not add any convention properties to the project.

24.7. Source set properties

The Groovy plugin adds the following convention properties to each source set in the project. You can use these properties in your build script as though they were properties of the source set object (see Section 21.3, “Conventions”).

Table 24.4. Groovy plugin - source set properties

Property name Type Default value Description
groovy SourceDirectorySet (read-only) Not null The Groovy source files of this source set. Contains all .groovy and .java files found in the Groovy source directories, and excludes all other types of files.
groovy.srcDirs Set<File>. Can set using anything described in Section 16.5, “Specifying a set of input files”. [projectDir/src/name/groovy] The source directories containing the Groovy source files of this source set. May also contain Java source files for joint compilation.
allGroovy FileTree (read-only) Not null All Groovy source files of this source set. Contains only the .groovy files found in the Groovy source directories.

These properties are provided by a convention object of type GroovySourceSet.

The Groovy plugin also modifies some source set properties:

Table 24.5. Groovy plugin - source set properties

Property name Change
allJava Adds all .java files found in the Groovy source directories.
allSource Adds all source files found in the Groovy source directories.

24.8. GroovyCompile

The Groovy plugin adds a GroovyCompile task for each source set in the project. The task type extends the JavaCompile task (see Section 23.11, “CompileJava”). Unless groovyOptions.useAnt is set to true, Gradle's native Groovy compiler integration is used. For most projects, this is the better choice than the Ant-based compiler. The GroovyCompile task supports most configuration options of the official Groovy compiler.

Table 24.6. Groovy plugin - GroovyCompile properties

Task Property Type Default Value
classpath FileCollection sourceSet.compileClasspath
source FileTree. Can set using anything described in Section 16.5, “Specifying a set of input files”. sourceSet.groovy
destinationDir File. sourceSet.output.classesDir
groovyClasspath FileCollection groovy configuration if non-empty; Groovy library found on classpath otherwise

[9] We are using the same conventions as introduced by Russel Winder's Gant tool (

[10] GroovyCompileGroovydocgroovyClasspathclasspathgroovy-all(-indy)groovy(-indy)groovyClasspathgroovyClasspath