Generate a Java file and include it in the sourceSet for compilation

Old Forum
1

As part of a build, I would want to generate one specific Java file from a template, then include it as part of the source set to be compiled.

Assuming that I might have something like

src/main/java/foo/bar.java
  src/main/java-templates/yin/yang.java.template

The first part is easy

task generateSource (type:Copy) {
  from('src/main/java-templates') {
    include '**/*.java.template'
  }
  into "${buildDir}/java"
  // Transform the content
  filter { .... }
  // And rename it to a .java file
  rename { ... }
}
  compileJava.dependsOn generateSource

The problem I have is, how to I add the generated files to the Java source set?

2

One way is to use the srcDir method of SourceDirectorySet

So something like

sourceSets {
    main {
        java {
            srcDir '<path to generated source>'
        }
    }
}
3

that would not work as it will result in a ‘Cannot add a SourceSet with name ‘main’ as a SourceSet with that name already exists.’

4

I don’t know how you’ve managed to produce that - can you provide the stack trace?

5

It is reproducible with something as simple as the following

apply plugin: 'java-base'
  sourceSets {
    main {
        java {
            srcDir new File( buildDir,'foo' )
        }
    }
}
  apply plugin: 'java'

Then run ‘gradle tasks --all’.

Context: If the example seems contrived, it is because it is a reflection of what happens in a plugin I am writing. I did not want to apply the ‘java’ plugin within my plugin, I just needed the source sets, so the ‘java-base’ is applied within my plugin. The idea was that the extra source will only get compiled when the user applies the ‘java’ plugin.

6

What you are doing using the code above is adding the main source set but what you want is to configure it if/when it’s added. The following will achieve that:

apply plugin: 'java-base'
sourceSets.matching { it.name == "main" } .all {
    it.java.srcDir new File(buildDir, 'foo')
}
apply plugin: 'java'
7

Sweet!