If we create our own tasks in Gradle, we usually extend from the DefaultTask or a subclass of DefaultTask. The tasks that are included with Gradle also extend from this class. Gradle will create a proxy class for the actual class implementation and adds (among other things) also a property setter method. The method has the name of the property and has a single argument of the same type as the property. It is different from the setProperty and getProperty methods already added by Groovy. For example, if we have a task with a property with the name message of type String then Gradle will add the method message(String) to the proxy class.

In the following example task, we have one property, user:

// File: buildSrc/src/main/groovy/com/mrhaki/gradle/Hello.groovy
package com.mrhaki.gradle

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

class Hello extends DefaultTask {
    String user

    @TaskAction
    void sayHello() {
        println "Hello $user, how are you doing?"
    }
}

With the following test, we can check that the method user(String) is actually created and we can use it to set a value for the user property:

// File: src/test/groovy/com/mrhaki/gradle/HelloTaskSpec.groovy
package com.mrhaki.gradle

import org.gradle.api.Project
import org.gradle.testfixtures.ProjectBuilder
import spock.lang.Specification
import spock.lang.Subject

class HelloTaskSpec extends Specification {

    @Subject
    private Hello task

    private Project project = ProjectBuilder.builder().build()

    def "user() method is generated to set user property"() {
        when:
        task = project.task('helloSample', type: Hello) {
            // Gradle generates proxy class to allow
            // 'setter(value)' methods for properties.
            // In this case we invoke user(String),
            // which maps to setUser(String).
            user 'sample'
        }

        then:
        task.user == 'sample'
    }

    def "Groovy syntax property assignment to set user property"() {
        when:
        task = project.task('helloSample', type: Hello) {
            // Groovy syntax for setUser(String).
            user = 'sample user'
        }

        then:
        task.user == 'sample user'
    }
}

The following build file has two tasks of type Hello where we use the user(String) method and a property assignment:

import com.mrhaki.gradle.Hello

task helloMrhaki(type: Hello) {
    user = 'mrhaki'
}

task helloHubert(type: Hello) {
    user 'Hubert'
}

The idea of this post came from watching a great presentation by Vitaliy Zasadnyy about Gradle plugins during a Mashup Gradle/Android Meetup.