解决jquery有正确返回值但不执行success函数的问题

$.ajax({
 url:'save',
 type:'POST',
 dataType:'json',
 contentType:'application/json',
 data:JSON.stringify({
 'loginName':login_name,
 'password':password,
 'name':name,
 'phone':phone,
 'sex':sex,
 'email':email
 }),
 success:function(result){
 if(result == 'success'){
 alert('注册成功，请到邮箱点击激活链接!');
 }
 },
 error:function(result){
 alert(result);
 }
});

@RequestMapping(value = "/save" , method = RequestMethod.POST)
@ResponseBody
public String save(@RequestBody User user , HttpSession session){
 ...
 return "success";
}