code: protected void callFetchService (PagedRequest request, AsyncCallback<R> callback)
      {
          callFetchService(request.offset, request.count, request.needCount, callback);
      }
docs: Calls the service to obtain data. Implementations should make a service call using the
  callback provided. If needCount is set, the implementation should also request the total
  number of items from the server (this is normally done in the same call that requests a
  page but may be optional for performance reasons). By default, this calls
  {@link #callFetchService(int, int, boolean, AsyncCallback)} method with the
  {@code requests}'s members.
  NOTE: subclasses must override one of the two callFetchService methods