Adding headers to Play Java async results

Chat.java

public static Result someAction() {
  Promise<Result> promise = Akka.asPromise(....);
  Promise<Result> modProm = applyHeader(promise);
  return async(modProm);
}


private static Promise<Result> applyHeader(Promise<Result> promise) {
  return promise.map(new Function<Result, Result>() {
    @Override
    public Result apply(Result result) throws Throwable {
      if (result.getWrappedResult() instanceof SimpleResult) {
        SimpleResult pr = (SimpleResult) result.getWrappedResult();
        Tuple2<String, String> ac = new Tuple2<String, String>(
          "Access-Control-Allow-Origin", "*");
        ArrayList<Tuple2<String, String>> list = new ArrayList<Tuple2<String, String>>();
        list.add(ac);
        scala.collection.immutable.List<Tuple2<String, String>> headers = 
          JavaConversions.asBuffer(list).toList();
        final PlainResult withHeaders = 
          pr.withHeaders(headers).as("text/json");
        return new Result() {
          @Override
          public play.api.mvc.Result getWrappedResult() {
            return withHeaders;
          }
        };
      } else
        return result;
    }
  });
}