fatjar.gradle

tasks.withType(Jar).allObjects { jar ->
   jar.merge = { fileCollection -> 
      // only resolve the file collection if the jar will be executed. This is important if people merge from dependency configurations. Otherwise the configuration would be always resolved
      // when the script is evaluated.
      gradle.taskGraph.whenReady { graph ->
         if (graph.hasTask(jar.path)) {
            fileCollection.files.each { archiveFile ->
               configure(jar) {
                  from zipTree(archiveFile)
               }
            }
         }
      }
   }
}