To use Groovy sources in our project, we can apply the Groovy plugin. The Groovy plugin makes it possible to compile Groovy source files to class files. The project can contain both Java and Groovy source files. The compiler that Gradle uses is a joint compiler that can compile Java and Groovy source files.

The plugin also adds new tasks to our build. To compile the Groovy source files, we can invoke the compileGroovy task. Test sources written in Groovy can be compiled with the compileTestGroovy task. Also, a compile<SourceSet>Groovy task is added for each extra source set in our build definition. So, if we create a new source set with the name api, there will be a compileApiGroovy task.

In the following example build file, we apply the Groovy plugin:

apply plugin: 'groovy' 

If we invoke the tasks task to see what is available, we get the following output:

$ gradle tasks
:tasks
------------------------------------------------------------
All tasks runnable...