Running a task within a custom task in Gradle

Question

I'm trying to write a custom Gradle plugin using Java. One of the things I'll need to do within this plugin is copy all the defined dependencies into a folder. I've found out how you can do this using a task in the build.gradle file:

task copyDeps(type: Copy) {
    from configurations.runtime
    into 'build/lib'
}

However, I'm struggling to figure out how I would run this task from within my own custom task. I've tried doing this:

public class MyTask extends DefaultTask {

    @TaskAction
    public void executeTask() {
        Copy copyTask = new Copy();
        copyTask.into(libFolder).from(getProject().getConfigurations().getByName("runtime").execute();
    }
}

However, when I run this I get the exception:

Task of type 'org.gradle.api.tasks.Copy' has been instantiated directly which is not supported. Tasks can only be created using the DSL.

I understand what it is trying to say, but I haven't been able to find out I would be able to execute this task using the DSL from within Java.

Answer 1

You can't create tasks within tasks in Gradle. If you want to write a custom plugin with a task as you have described, the way to go is to write a custom plugin class and within that plugin class you declare a task of type Copy that does what you want to do. This could look like this:

class MyCustomPlugin extends Plugin<Project> {

    void apply(Project project) {
        project.tasks.create("copyDeps", Copy.class) {
            from configurations.runtime
            into 'build/lib'
        }
    }

}

Now, if you apply this plugin within your buildscript:

apply plugin:MyCustomPlugin

you automatically have a task named "copyDeps" of type Copy in your build.

One more thing:

Sometimes it can be convenient to do a simple copy operation in a custom task. This can be done using the project.copy util method. A task like this would look this

public class MyTask extends DefaultTask {

    @TaskAction
    public void executeTask() {
        project.copy {
            into(libFolder)
            from(project.configurations.runtime)
        }
    }
}

With plain java it would look like this:

public class MyTask extends DefaultTask {

    @TaskAction
    public void executeTask() {
        project.copy(new Action<CopySpec>() {
            @Override
            void execute(CopySpec copySpec) {
                copySpec.into(libFolder);
                copySpec.from(getProject().getConfigurations().getByName("runtime"));
            }
        });

    }
}

One last thing:

You should never call Task#execute() your own. This method is considered to be internal API in Gradle and executing it directly causes unexpected behaviour. (for example it breaks Gradles' incremental build feature)