title: how can return json using response.senderror
body: <p>In my app,I use springMVC and tomcat,my controller return object,but when something wrong,I only want return some string message with content tye json,so I use response.error, but it not work,the return is a html.
  my controller:</p>
  
  <pre><code>@RequestMapping(value = "{id}/{name}" ,method=RequestMethod.POST,produces = MediaType.APPLICATION_JSON_VALUE)
  
  public @ResponseBody UserBean  login(@PathVariable String id,@PathVariable("name") String userName,
          @RequestHeader(value = "User-Agent") String user_agen,
          @CookieValue(required = false) Cookie userId,
          HttpServletRequest request,HttpServletResponse response,@RequestBody UserBean entity
          ) throws IOException {
       System.out.println("dsdsd");
       System.out.print(userName);
  
       response.setContentType( MediaType.APPLICATION_JSON_VALUE);
       response.sendError(HttpServletResponse.SC_BAD_REQUEST, "somethind wrong");
       return  null;
  </code></pre>