关于RestTemplate postForObject方法请求 服务端Controller接受不到值的问题解决

@Autowired
RestTemplate restTemplate;

发送请求的controller方法
@RequestMapping(value = "/update", method = RequestMethod.POST)
public String update(User user) {
    return restTemplate.postForObject(REST_URL_PREFIX+"/cloud/update", user, String.class);
} 

接受请求的controller方法
@RestController 
@RequestMapping("/cloud") 
public class UserController {
  //这里一定要用@RequestBody 注解接收--Controller接受不到值的根本原因
  @RequestMapping(value = "/update", method = RequestMethod.POST)
  public String update(@RequestBody User user) {
      if(user.getId() == null){
          return "传值为空";
      }else if (userService.update(user)) {
        return "修改成功";
      } else {
          return "修改失败";
      }
  }

成功返回

@RequestMapping(value = "/update", method = RequestMethod.POST)
public String update(User user) {
    if(user.getId() == null){
        return "传值为空";
    }else if (userService.update(user)) {
        return "修改成功";
    } else {
        return "修改失败";
    }
}