Chapter 8. Mixed Languages

We have seen how to use Gradle for projects with Java code. Gradle has support for other languages as well. In the last couple of years, other languages for JVM have emerged. In this chapter, we will take a look at Gradle's support for Groovy and Scala languages. Both languages are supported by JVM.

We will see how to apply the correct plugin and configuration to our Gradle build files to work with the different languages.

Gradle also supports C. The C plugin adds support to compile source files. JavaScript and Closure plugins are available as third-party plugins, which add support for these languages. We will not cover this support in this book. We will focus on the JVM languages-Groovy and Scala.

Using the Groovy plugin

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...

Using the Scala plugin

We can also use Gradle to work with Scala source files. We can have a Scala-only project or both Java and Scala source files in our project. We must apply the Scala plugin to enable the Scala support for our build. The plugin adds new tasks to compile the Scala source files. With the compileScala task, we compile our main Scala source files. The source files must be in the src/main/scala directory. The compileTestScala task compiles all Scala source code files that are in the src/test/scala directory. The plugin also adds a compile<SourceSet>Scala task for custom-defined source sets in our build.

The compile tasks support both Java and Scala source files with joint compilation. We can place our Java source files in say the  src/main/java directory of our project and the Scala source files in the src/main/scala directory. The compiler will compile both types of files. To be able to compile the files, we must add dependencies to the Scala library in our build file...

Summary

In this chapter, we discussed how to work with Groovy and Scala sources in a Gradle project. We applied the either Groovy or Scala plugins to our project and saw that Gradle added the tasks to compile the source files to the project. We also discussed that we must add a dependency to the correct Groovy or Scala version of the dependency configuration added by the plugin. Both plugins will include the Java plugin as well.

We also discussed that the plugins also provide some new properties for source sets so that we can, for example, find all Groovy or Scala source files in a source set.

In the next chapter, we will take a look at how to add code quality tools to our Gradle builds.