code: public void getSubFolders(final String folder, final AsyncCallback<List<CmsVfsEntryBean>> callback) {
  
          CmsRpcAction<List<CmsVfsEntryBean>> action = new CmsRpcAction<List<CmsVfsEntryBean>>() {
  
              @Override
              public void execute() {
  
                  start(0, false);
                  getGalleryService().getSubFolders(folder, this);
              }
  
              @Override
              protected void onResponse(List<CmsVfsEntryBean> result) {
  
                  stop(false);
                  callback.onSuccess(result);
              }
  
          };
          action.execute();
      }
docs: Retrieves the sub-folders of a given folder.<p>
  
  @param folder the folder whose sub-folders should be retrieved
  @param callback the callback for processing the sub-folders