public class MyController extends Controller {
    public static CompletionStage<Result> index() {
        CompletionStage<GenericTask> promiseOfGenericTask1 =
                CompletableFuture.supplyAsync(
                        MyController::doGenericTask1
                );
        CompletionStage<GenericTask> promiseOfGenericTask2 =
                CompletableFuture.supplyAsync(
                        MyController::doGenericTask2
                );

        CompletionStage<List<GenericTask>> cStages =
                Futures.sequence(promiseOfGenericTask1, promiseOfGenericTask2);
        return cStages.thenApplyAsync(
                gTasks -> ok(result.render((List<GenericTask>) gTasks))
        );
    }
..........
}