问GWT RPC机制如何使用非void返回类型

EN

@RemoteServiceRelativePath("show_box")
public interface ShowBoxCommandService extends RemoteService{

 public ArrayList<String> showBox();

}

public ArrayList<String> showBox() {

  ArrayList<String> box = new ArrayList<String>();
  Iterator<Box> boxes = BoxRegistry.getInstance().getBoxes();
  while (boxes.hasNext()) {
     box.add(boxes.next().toString());
  }
  return box;
}

 AsyncCallback<Void> callback = new AsyncCallback<Void>() {
           public void onFailure(Throwable caught) {
              // TODO: Do something with errors.
              // console was not started properly
           }

           @Override
           public void onSuccess(Void result) {
              // TODO Auto-generated method stub
              // dialog saying that the console is started succesfully

           }
        };

    public interface ShowBoxCommandServiceAsync {

   void showBox(AsyncCallback<ArrayList<String>> callback);

  }