@RequestMapping(value = "info", method = RequestMethod.POST)
 @ResponseBody
 public ResponseEntity<String> doGetUserInfo(HttpServletRequest request) throws Exception {
   User user = (User) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
   StringBuilder out = new StringBuilder();
   out.append("{ \"user\" : ");
   out.append(
       String.format(
           "{ \"id\" : \"%s\" , \"realname\" : \"%s\" , \"username\" : \"%s\"}",
           user.getId(), user.getRealname(), user.getUsername()));
   out.append("}");
   HttpHeaders headers = new HttpHeaders();
   headers.set("Content-Type", "application/json");
   return new ResponseEntity<String>(out.toString(), headers, HttpStatus.OK);
 }