private void updateUrl() {
   final String uploadUrl =
       GWT.getHostPageBaseURL()
           + "fileupload;jsessionid="
           + session.getSessionId()
           + "?end="
           + totalSize
           + "&start="
           + bytesUploaded
           + "&clientId="
           + clientId
           + "&lastUpload="
           + ((filesUploaded + 1) == numFiles);
   upload.setUploadURL(uploadUrl);
 }