code: protected void handleFileUploadRequest(final WMultiFileWidget widget, final XmlStringBuilder xml, final String uploadId) {
  
  		FileWidgetUpload file = widget.getFile(uploadId);
  		if (file == null) {
  			throw new SystemException("Invalid file id [" + uploadId + "] to render uploaded response.");
  		}
  		int idx = widget.getFiles().indexOf(file);
  		FileWidgetRendererUtil.renderFileElement(widget, xml, file, idx);
  	}
docs: Paint the response for the file uploaded in this request.
  
  @param widget the file widget to render
  @param xml the XML string builder
  @param uploadId the file id uploaded in this request