Mix Groovy and Java in STS 3.7.3.RELEASE

To mix Java and Groovy together in the same Spring Starter project, a few changes can be made to the project's properties and paths. By default, when a Java project is created it only looks for source files and test files in the src/main/java and src/test/java directories.

Add src/main/groovy to Java Build Path

1. Create the src/main/groovy directory
2. Right-click the project in Package Explorer, then click Properties
3. Click Java Build Path in the left sidebar
4. Click Add Folder... to add src/main/groovy

Add Groovy libraries to classpath

1. Right-click the project in Package Explorer
2. Expand Groovy, then click Add Groovy libraries to classpath

Only include groovy-all

At this point, trying to run the Spring Boot app will generate errors that look like this.

...
org.apache.catalina.core.ContainerBase : A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[]]
...

The errors can be resolved by removing the extra libraries STS automatically added in the previous step.

1. Right-click Groovy Libraries in the project
2. Click Properties
3. Select "No, only include groovy-all" in the first panel that asks, "Should all jars in the groovy-eclipse lib folder be included on the classpath?"