SourceSetOutput

plugins {
    id 'java'
}

sourceSets {
  main {
    //if you truly want to override the defaults:
    output.resourcesDir = file('out/bin')
    // Compiled Java classes should use this directory
    java.destinationDirectory.set(file('out/bin'))
  }
}

plugins {
  id 'java'
}

def generateResourcesTask = tasks.register("generate-resources", GenerateResourcesTask) {
  resourcesDir.set(layout.buildDirectory.dir("generated-resources/main"))
}

// Include all outputs of the `generate-resources` task as outputs of the main sourceSet.
sourceSets {
  main {
    output.dir(generateResourcesTask)
  }
}

abstract class GenerateResourcesTask extends DefaultTask {
  @OutputDirectory
  abstract DirectoryProperty getResourcesDir()

  @TaskAction
  def generateResources() {
    def generated = resourcesDir.file("myGeneratedResource.properties").get().asFile
    generated.text = "message=Stay happy!"
  }
}