@ResponseBody
 @RequestMapping(value = "/checkEmailExists", produces = "application/json")
 public AjaxResponse checkEmailExists(@RequestParam("email") String email) {
   boolean exists = userBO.checkEmailExists(email);
   if (exists) {
     return new AjaxResponseBuilder().notOk().error("Email [" + email + "] already exist").build();
   } else {
     return new AjaxResponseBuilder().ok().build();
   }
 }