View source for Extending Gradle with a Custom Enhanced Task

=Internal=
* [[Gradle_Task#Enhanced_Task|Gradle Tasks &#124; Enhanced Tasks]]

=Overview=
An [[Gradle_Task#Enhanced_Task|enhanced task]] requires writing Groovy or Java code either in [[Extending_Gradle#In-line_in_build.gradle|in-line in build.gradle]] or [[Extending_Gradle#In-line_in_a_script_plugin|a script plugin file]], or into a source code file (or files) maintained in [[Extending_Gradle#In_the_Project.27s_buildSrc_Directory|the project's buildSrc]] or [[Extending_Gradle#External_to_Project|externally]]. The behavior is built into the task and the task exposes some properties that can be configured from the build script.
=In-Line Custom Enhanced Task=
An in-line custom enhanced task can be declared as follows, either in [[build.gradle]] or in a [[Gradle_Plugin_Concepts#Script_Plugin|script plugin]]:
<syntaxhighlight lang='groovy'>
...
class CustomEnhancedTask extends DefaultTask {
    @TaskAction
    void impl() {
        System.out.println("this is an in-line enhanced task")
    }
}

task customTask(type: CustomEnhancedTask)
...
</syntaxhighlight>

Example: {{External|[https://github.com/ovidiuf/playground/tree/master/gradle/extending-gradle/04-in-line-build-gradle-enhanced-task Custom enhanced Java task declared in-line in build.gradle]}}

This approach is not recommended as we are losing testability and reusability of the task.

=File-Based Custom Enhanced Task=

The same task can be defined in a Java/Groovy/Kotlin file either in the [[Extending_Gradle#In_the_Project.27s_buildSrc_Directory|project's buildSrc]] or in an [[Extending_Gradle#External_Standalone_Project|external project]]:
<syntaxhighlight lang='java'>
package playground.gradle;

import org.gradle.api.DefaultTask;
import org.gradle.api.tasks.TaskAction;

public class CustomEnhancedTask extends DefaultTask {
   @TaskAction
   void impl() {
      System.out.println("this is an custom enhanced task developed in buildSrc");
   }
}
</syntaxhighlight>

If the task was defined in the [[Extending_Gradle#In_the_Project.27s_buildSrc_Directory|project's buildSrc]], then it can then be declared in build.gradle as follows. The task name is arbitrary, it does not have to match the class name, but matching names is intuitive and thus preferred.
<syntaxhighlight lang='groovy'>
task customEnhancedTask(type: playground.gradle.CustomEnhancedTask)
</syntaxhighlight>

Example: {{External|[https://github.com/ovidiuf/playground/tree/master/gradle/extending-gradle/03-enhanced-task-in-buildSrc Custom enhanced task developed in buildSrc]}}

If the task was defined in an [[Extending_Gradle#External_Standalone_Project|external project]], the external project must publish the JAR containing the task in a repository, and the Gradle project using the task must declare the JAR as dependency in the buildScript block of the build.gradle file and pull it from the repository it was published in:
<syntaxhighlight lang='groovy'>
buildscript {
    repositories {
        mavenLocal()
    }
    dependencies {
        classpath 'playground.gradle.standalone-task:06-enhanced-task-developed-in-standalone-project:0.1.0'
    }
}

task custEnhTask(type: playground.gradle.CustomEnhancedTask)
</syntaxhighlight>
More details on configuring the build script classpath are available in: {{Internal|Gradle Build Script Classpath|Build Script Classpath}}
Examples:
{{External|[https://github.com/ovidiuf/playground/tree/master/gradle/extending-gradle/06-enhanced-task-developed-in-standalone-project Custom enhanced task developed in standalone project]}}
{{External|[https://github.com/ovidiuf/playground/tree/master/gradle/extending-gradle/07-enhanced-task-imported-from-external-project Custom enhanced task imported from external project]}}

=<span id='Enhanced_Task_Implementation_Details'></span><span id='Enhanced_Custom_Task_Implementation_Details'></span>Programming Custom Tasks=

==@TaskAction==
{{External|[https://docs.gradle.org/current/javadoc/org/gradle/api/tasks/TaskAction.html org.gradle.api.tasks.TaskAction]}}

==Action Failure==

If the action code fails in any way, we indicate that the action, and thus the task failed by throwing an unchecked exception. RuntimeException works. Gradle will display the exception message:
<syntaxhighlight lang='text'>
./gradlew example
> Task :example FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':example'.
> this is the RuntimeException message
[...]
</syntaxhighlight>
==Logging==
{{Internal|Gradle_Logging#Accessing_Gradle_Logging_in_Custom_Java_Tasks|Accessing Gradle Logging in Custom Java Tasks}}

==Allowing Configuration via a Task Constructor==
{{External|https://docs.gradle.org/current/userguide/more_about_tasks.html#sec:passing_arguments_to_a_task_constructor}}
Configuration values can be passed to a Task's class constructor, if the respective constructor was annotated with @javax.inject.Inject:
<syntaxhighlight lang='java'>
class CustomTask extends DefaultTask {
  final String message
  final int number

  @Inject
  CustomTask(String message, int number) { 
    this.message = message
    this.number = number
  } 
}
</syntaxhighlight>
The task can then be configured with constructor arguments using the [[Gradle_Project#Task_Container|task container]], as shown below. This should be the preferred way of configuring tasks, as it improves the configuration time. For more details, see [[Gradle_Task#Task_Configuration_Avoidance_APIs|Gradle Tasks &#124; Task Configuration Avoidance APIs]].
<syntaxhighlight lang='groovy'>
tasks.create('myTask', CustomTask, 'hello', 42)
task myTask(type: CustomTask, constructorArgs: ['hello', 42])
</syntaxhighlight>
In all circumstances, the values passed as constructor arguments must be non-null. If a null value is passed, Gradle will throw a NullPointerException.
==Programmatic Access to Properties==
{{Internal|Gradle_Extra_Properties#Programmatic_Access_to_Extra_Properties|Gradle Extra Properties &#124; Programmatic Access to Extra Properties}}

==TODO==

<font color=darkgray>
The name of the method annotated with [[Gradle_Task#.40TaskAction|@TaskAction]] is arbitrary.

TODO:
* Gradle in Action Section 8.3.2 Using the CloudBees API from tasks.
* Gradle in Action Section 8.4 Writing custom task classes.
* https://docs.gradle.org/current/userguide/custom_tasks.html
</font>

=Enhanced Task Testing=
<font color=darkgray>TODO https://docs.gradle.org/current/userguide/custom_tasks.html#sec:writing_tests_for_your_task_class</font>

=TODO/TODEPLETE=
<font color=orange>DEPLETE [[Gradle_Task_TODEPLETE#Explicit_Task_Declaration_.28Custom_Tasks.29]]</font>