Authoring Tasks
In the introductory tutorial 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 tasks that have their own properties and methods. Such tasks are either provided by you or built into Gradle.
Task outcomes
When Gradle executes a task, it can label the task with different outcomes in the console UI and via the Tooling API. These labels are based on if a task has actions to execute, if it should execute those actions, if it did execute those actions and if those actions made any changes.
(no label)
orEXECUTED
-
Task executed its actions.
-
Task has actions and Gradle has determined they should be executed as part of a build.
-
Task has no actions and some dependencies, and any of the dependencies are executed. See also Lifecycle Tasks.
-
UP-TO-DATE
-
Task’s outputs did not change.
-
Task has outputs and inputs and they have not changed. See Incremental Build.
-
Task has actions, but the task tells Gradle it did not change its outputs.
-
Task has no actions and some dependencies, but all of the dependencies are up-to-date, skipped or from cache. See also Lifecycle Tasks.
-
Task has no actions and no dependencies.
-
FROM-CACHE
-
Task’s outputs could be found from a previous execution.
-
Task has outputs restored from the build cache. See Build Cache.
-
SKIPPED
-
Task did not execute its actions.
-
Task has been explicitly excluded from the command-line. See Excluding tasks from execution.
-
Task has an
onlyIf
predicate return false. See Using a predicate.
-
NO-SOURCE
-
Task did not need to execute its actions.
-
Task has inputs and outputs, but no sources. For example, source files are
.java
files for JavaCompile.
-
Defining tasks
We have already seen how to define tasks using strings for task names in this chapter. There are a few variations on this style, which you may need to use in certain situations.
The task configuration APIs are described in more detail in the task configuration avoidance chapter. |
tasks.register("hello") {
doLast {
println("hello")
}
}
tasks.register<Copy>("copy") {
from(file("srcDir"))
into(buildDir)
}
tasks.register('hello') {
doLast {
println 'hello'
}
}
tasks.register('copy', Copy) {
from(file('srcDir'))
into(buildDir)
}
We add the tasks to the tasks
collection.
Have a look at TaskContainer for more variations of the register()
method.
In the Kotlin DSL there is also a specific delegated properties syntax that is useful if you need the registered task for further reference.
// Using Kotlin delegated properties
val hello by tasks.registering {
doLast {
println("hello")
}
}
val copy by tasks.registering(Copy::class) {
from(file("srcDir"))
into(buildDir)
}
// Assigning registered tasks to a variable in Groovy
def hello = tasks.register('hello') {
doLast {
println 'hello'
}
}
def copy = tasks.register('copy', Copy) {
from(file('srcDir'))
into(buildDir)
}
If you look at the API of the tasks container you may notice that there are additional methods to create tasks. The use of these methods is discouraged and will be deprecated in future versions. These methods only exist for backward compatibility as they were introduced before task configuration avoidance was added to Gradle. |
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, just like with defining tasks there are language specific syntaxes for the Groovy and Kotlin DSL:
In general, tasks are available through the tasks
collection.
You should use the methods that return a task provider – register()
or named()
– to make sure you do not break task configuration avoidance.
tasks.register("hello")
tasks.register<Copy>("copy")
println(tasks.named("hello").get().name) // or just 'tasks.hello' if the task was added by a plugin
println(tasks.named<Copy>("copy").get().destinationDir)
tasks.register('hello')
tasks.register('copy', Copy)
println tasks.named('hello').get().name
println tasks.named('copy').get().destinationDir
Tasks of a specific type can also be accessed by using the tasks.withType()
method.
This enables to easily avoid duplication of code and reduce redundancy.
tasks.withType<Tar>().configureEach {
enabled = false
}
tasks.register("test") {
dependsOn(tasks.withType<Copy>())
}
tasks.withType(Tar).configureEach {
enabled = false
}
tasks.register('test') {
dependsOn tasks.withType(Copy)
}
The following shows how to access a task by path. This is not a recommended practice anymore as it breaks task configuration avoidance and project isolation. Dependencies between projects should be declared as dependencies. |
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.
tasks.register("hello")
tasks.register("hello")
println(tasks.getByPath("hello").path)
println(tasks.getByPath(":hello").path)
println(tasks.getByPath("project-a:hello").path)
println(tasks.getByPath(":project-a:hello").path)
tasks.register('hello')
tasks.register('hello')
println tasks.getByPath('hello').path
println tasks.getByPath(':hello').path
println tasks.getByPath('project-a:hello').path
println tasks.getByPath(':project-a:hello').path
gradle -q hello
> gradle -q hello :hello :hello :project-a:hello :project-a:hello
Have a look at TaskContainer for more options for locating tasks.
Configuring tasks
As an example, let’s look at the Copy
task provided by Gradle.
To register a Copy
task for your build, you can declare in your build script:
tasks.register<Copy>("myCopy")
tasks.register('myCopy', Copy)
This registers 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 type Copy
.
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.
tasks.named<Copy>("myCopy") {
from("resources")
into("target")
include("**/*.txt", "**/*.xml", "**/*.properties")
}
tasks.named('myCopy') {
from 'resources'
into 'target'
include('**/*.txt', '**/*.xml', '**/*.properties')
}
You can also store the task reference in a variable and use to configure the task further at a later point in the script.
// Configure task using Kotlin delegated properties and a lambda
val myCopy by tasks.existing(Copy::class) {
from("resources")
into("target")
}
myCopy {
include("**/*.txt", "**/*.xml", "**/*.properties")
}
// Configure task through a task provider
def myCopy = tasks.named('myCopy') {
from 'resources'
into 'target'
}
myCopy.configure {
include('**/*.txt', '**/*.xml', '**/*.properties')
}
Have a look at TaskContainer for more options for configuring tasks.
If you use the Kotlin DSL and the task you want to configure was added by a plugin, you can use a convenient accessor for the task.
That is, instead of |
You can also use a configuration block when you define a task.
tasks.register<Copy>("copy") {
from("resources")
into("target")
include("**/*.txt", "**/*.xml", "**/*.properties")
}
tasks.register('copy', 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 |
Passing arguments to a task constructor
As opposed to configuring the mutable properties of a Task
after creation, you can pass argument values to the Task
class’s constructor.
In order to pass values to the Task
constructor, you must annotate the relevant constructor with @javax.inject.Inject
.
@Inject
constructorabstract class CustomTask @Inject constructor(
private val message: String,
private val number: Int
) : DefaultTask()
abstract class CustomTask extends DefaultTask {
private final String message
private final int number
@Inject
CustomTask(String message, int number) {
this.message = message
this.number = number
}
}
You can then create a task, passing the constructor arguments at the end of the parameter list.
tasks.register<CustomTask>("myTask", "hello", 42)
tasks.register('myTask', CustomTask, 'hello', 42)
It’s recommended to use the Task Configuration Avoidance APIs to improve configuration time. |
In all circumstances, the values passed as constructor arguments must be non-null.
If you attempt to pass a null
value, Gradle will throw a NullPointerException
indicating which runtime value is null
.
Adding dependencies to a task
There are several ways you can define the dependencies of a task. In 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 project-a:taskX
to project-b:taskY
:
project("project-a") {
tasks.register("taskX") {
dependsOn(":project-b:taskY")
doLast {
println("taskX")
}
}
}
project("project-b") {
tasks.register("taskY") {
doLast {
println("taskY")
}
}
}
project('project-a') {
tasks.register('taskX') {
dependsOn ':project-b:taskY'
doLast {
println 'taskX'
}
}
}
project('project-b') {
tasks.register('taskY') {
doLast {
println 'taskY'
}
}
}
gradle -q taskX
> gradle -q taskX taskY taskX
Instead of using a task name, you can define a dependency using a TaskProvider
object, as shown in this example:
val taskX by tasks.registering {
doLast {
println("taskX")
}
}
val taskY by tasks.registering {
doLast {
println("taskY")
}
}
taskX {
dependsOn(taskY)
}
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
}
}
def taskY = tasks.register('taskY') {
doLast {
println 'taskY'
}
}
taskX.configure {
dependsOn taskY
}
gradle -q taskX
> gradle -q taskX taskY taskX
For more advanced uses, you can define a task dependency using a lazy block.
When evaluated, the block is passed the task whose dependencies are being calculated.
The lazy block 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
:
val taskX by tasks.registering {
doLast {
println("taskX")
}
}
// Using a Gradle Provider
taskX {
dependsOn(provider {
tasks.filter { task -> task.name.startsWith("lib") }
})
}
tasks.register("lib1") {
doLast {
println("lib1")
}
}
tasks.register("lib2") {
doLast {
println("lib2")
}
}
tasks.register("notALib") {
doLast {
println("notALib")
}
}
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
}
}
// Using a Gradle Provider
taskX.configure {
dependsOn(provider {
tasks.findAll { task -> task.name.startsWith('lib') }
})
}
tasks.register('lib1') {
doLast {
println('lib1')
}
}
tasks.register('lib2') {
doLast {
println('lib2')
}
}
tasks.register('notALib') {
doLast {
println('notALib')
}
}
gradle -q taskX
> gradle -q taskX lib1 lib2 taskX
For more information about task dependencies, see the Task API.
Ordering tasks
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: e.g. 'build' never runs before 'clean'.
-
Run build validations early in the build: e.g. 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: e.g. unit tests should run before integration tests.
-
A task that aggregates the results of all tasks of a particular type: e.g. 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.
val taskX by tasks.registering {
doLast {
println("taskX")
}
}
val taskY by tasks.registering {
doLast {
println("taskY")
}
}
taskY {
mustRunAfter(taskX)
}
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
}
}
def taskY = tasks.register('taskY') {
doLast {
println 'taskY'
}
}
taskY.configure {
mustRunAfter taskX
}
gradle -q taskY taskX
> gradle -q taskY taskX taskX taskY
val taskX by tasks.registering {
doLast {
println("taskX")
}
}
val taskY by tasks.registering {
doLast {
println("taskY")
}
}
taskY {
shouldRunAfter(taskX)
}
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
}
}
def taskY = tasks.register('taskY') {
doLast {
println 'taskY'
}
}
taskY.configure {
shouldRunAfter taskX
}
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:
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
andB
independently. The ordering rule only has an effect when both tasks are scheduled for execution. -
When run with
--continue
, it is possible forB
to execute in the event thatA
fails.
As mentioned before, the “should run after” ordering rule will be ignored if it introduces an ordering cycle:
val taskX by tasks.registering {
doLast {
println("taskX")
}
}
val taskY by tasks.registering {
doLast {
println("taskY")
}
}
val taskZ by tasks.registering {
doLast {
println("taskZ")
}
}
taskX { dependsOn(taskY) }
taskY { dependsOn(taskZ) }
taskZ { shouldRunAfter(taskX) }
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
}
}
def taskY = tasks.register('taskY') {
doLast {
println 'taskY'
}
}
def taskZ = tasks.register('taskZ') {
doLast {
println 'taskZ'
}
}
taskX.configure { dependsOn(taskY) }
taskY.configure { dependsOn(taskZ) }
taskZ.configure { shouldRunAfter(taskX) }
gradle -q taskX
> gradle -q taskX taskZ taskY taskX
Adding a description to a task
You can add a description to your task. This description is displayed when executing gradle tasks
.
tasks.register<Copy>("copy") {
description = "Copies the resource directory to the target directory."
from("resources")
into("target")
include("**/*.txt", "**/*.xml", "**/*.properties")
}
tasks.register('copy', Copy) {
description 'Copies the resource directory to the target directory.'
from 'resources'
into 'target'
include('**/*.txt', '**/*.xml', '**/*.properties')
}
Skipping tasks
Gradle offers multiple ways to skip the execution of a task.
Using a predicate
You can use Task.onlyIf
to attach a predicate to a task. The task’s actions are only executed if the predicate evaluates to true. The predicate 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 executed.
Passing an optional reason string to onlyIf()
is useful for explaining why the task is skipped.
val hello by tasks.registering {
doLast {
println("hello world")
}
}
hello {
val skipProvider = providers.gradleProperty("skipHello")
onlyIf("there is no property skipHello") {
!skipProvider.isPresent()
}
}
def hello = tasks.register('hello') {
doLast {
println 'hello world'
}
}
hello.configure {
def skipProvider = providers.gradleProperty("skipHello")
onlyIf("there is no property skipHello") {
!skipProvider.present
}
}
gradle hello -PskipHello
> gradle hello -PskipHello > Task :hello SKIPPED BUILD SUCCESSFUL in 0s
It is possible to find the reason for a task being skipped by running the build with the --info
logging level.
gradle hello -PskipHello --hello
> gradle hello -PskipHello --info ... > Task :hello SKIPPED Skipping task ':hello' as task onlyIf 'there is no property skipHello' is false. :hello (Thread[included builds,5,main]) completed. Took 0.018 secs. BUILD SUCCESSFUL in 13s
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.
val compile by tasks.registering {
doLast {
println("We are doing the compile.")
}
}
compile {
doFirst {
// Here you would put arbitrary conditions in real life.
if (true) {
throw StopExecutionException()
}
}
}
tasks.register("myTask") {
dependsOn(compile)
doLast {
println("I am not affected")
}
}
def compile = tasks.register('compile') {
doLast {
println 'We are doing the compile.'
}
}
compile.configure {
doFirst {
// Here you would put arbitrary conditions in real life.
if (true) {
throw new StopExecutionException()
}
}
}
tasks.register('myTask') {
dependsOn('compile')
doLast {
println 'I am not affected'
}
}
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.[1]
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. A disabled task will be labelled SKIPPED.
val disableMe by tasks.registering {
doLast {
println("This should not be printed if the task is disabled.")
}
}
disableMe {
enabled = false
}
def disableMe = tasks.register('disableMe') {
doLast {
println 'This should not be printed if the task is disabled.'
}
}
disableMe.configure {
enabled = false
}
gradle disableMe
> gradle disableMe > Task :disableMe SKIPPED BUILD SUCCESSFUL in 0s
Task timeouts
Every task has a timeout
property which can be used to limit its execution time.
When a task reaches its timeout, its task execution thread is interrupted.
The task will be marked as failed. Finalizer tasks will still be run.
If --continue
is used, other tasks can continue running after it.
Tasks that don’t respond to interrupts can’t be timed out.
All of Gradle’s built-in tasks respond to timeouts in a timely manner.
tasks.register("hangingTask") {
doLast {
Thread.sleep(100000)
}
timeout.set(Duration.ofMillis(500))
}
tasks.register("hangingTask") {
doLast {
Thread.sleep(100000)
}
timeout = Duration.ofMillis(500)
}
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:
tasks.addRule("Pattern: ping<ID>") {
val taskName = this
if (startsWith("ping")) {
task(taskName) {
doLast {
println("Pinging: " + (taskName.replace("ping", "")))
}
}
}
}
tasks.addRule("Pattern: ping<ID>") { String taskName ->
if (taskName.startsWith("ping")) {
task(taskName) {
doLast {
println "Pinging: " + (taskName - 'ping')
}
}
}
}
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:
tasks.addRule("Pattern: ping<ID>") {
val taskName = this
if (startsWith("ping")) {
task(taskName) {
doLast {
println("Pinging: " + (taskName.replace("ping", "")))
}
}
}
}
tasks.register("groupPing") {
dependsOn("pingServer1", "pingServer2")
}
tasks.addRule("Pattern: ping<ID>") { String taskName ->
if (taskName.startsWith("ping")) {
task(taskName) {
doLast {
println "Pinging: " + (taskName - 'ping')
}
}
}
}
tasks.register('groupPing') {
dependsOn 'pingServer1', 'pingServer2'
}
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.
Finalizer tasks
Finalizer tasks are automatically added to the task graph when the finalized task is scheduled to run.
val taskX by tasks.registering {
doLast {
println("taskX")
}
}
val taskY by tasks.registering {
doLast {
println("taskY")
}
}
taskX { finalizedBy(taskY) }
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
}
}
def taskY = tasks.register('taskY') {
doLast {
println 'taskY'
}
}
taskX.configure { finalizedBy taskY }
gradle -q taskX
> gradle -q taskX taskX taskY
Finalizer tasks will be executed even if the finalized task fails or if the finalized task is considered up to date.
val taskX by tasks.registering {
doLast {
println("taskX")
throw RuntimeException()
}
}
val taskY by tasks.registering {
doLast {
println("taskY")
}
}
taskX { finalizedBy(taskY) }
def taskX = tasks.register('taskX') {
doLast {
println 'taskX'
throw new RuntimeException()
}
}
def taskY = tasks.register('taskY') {
doLast {
println 'taskY'
}
}
taskX.configure { finalizedBy taskY }
gradle -q taskX
> gradle -q taskX taskX taskY FAILURE: Build failed with an exception. * Where: Build file '/home/user/gradle/samples/build.gradle' line: 4 * What went wrong: Execution failed for task ':taskX'. > java.lang.RuntimeException (no error message) * Try: > Run with --stacktrace option to get the stack trace. > Run with --info or --debug option to get more log output. > Run with --scan to get full insights. > Get more help at https://help.gradle.org. BUILD FAILED in 0s
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…).
Lifecycle tasks
Lifecycle tasks are tasks that do not do work themselves. They typically do not have any task actions. Lifecycle tasks can represent several concepts:
-
a work-flow step (e.g., run all checks with
check
) -
a buildable thing (e.g., create a debug 32-bit executable for native components with
debug32MainExecutable
) -
a convenience task to execute many of the same logical tasks (e.g., run all compilation tasks with
compileAll
)
The Base Plugin defines several standard lifecycle tasks, such as build
, assemble
, and check
. All the core language plugins, like the Java Plugin, apply the Base Plugin and hence have the same base set of lifecycle tasks.
Unless a lifecycle task has actions, its outcome is determined by its task dependencies. If any of those dependencies are executed, the lifecycle task will be considered EXECUTED
. If all of the task dependencies are up to date, skipped or from cache, the lifecycle task will be considered UP-TO-DATE
.
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.
Moved documentation
Some documentation previously appearing in this chapter has been moved to the Incremental Build chapter.
Up-to-date checks (AKA Incremental Build)
Moved to the Incremental Build chapter.
Custom task types
Moved to a section under Incremental Build.
Nested inputs
Moved to a section under Incremental Build.
Runtime validation
Moved to a section under Incremental Build.
Runtime API
Moved to a section under Incremental Build.
Continuous build
Moved to a section under Incremental Build.
Task parallelism
Moved to a section under Incremental Build.
How does it work?
Moved to a section under Incremental Build.
Advanced techniques
Moved to a section under Incremental Build.
Integrate an external tool which does its own up-to-date checking
Moved to a section under Incremental Build.
Stale task outputs
Moved to a section under Incremental Build.
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 Default imports).