HttpServletRequest无法获取数据

Question

请求网址：http://localhost:8080/deduct/migration/export?fromId=872

java代码：

@RequestMapping(value = "/export", method = RequestMethod.GET)
public void export(HttpServletRequest request,@RequestParam(value="fromId") String from ) throws IOException {
  String fromId=request.getParameter("fromId");//fromId=null
  System.out.println(from);//from=872
}

为什么＆＃39; request.getParameter（fromId）＆＃39;是空的吗？

请帮助我，感激不尽！

我添加了＃34;＆＃34;，但忘记填写问题，抱歉