@RequestMapping(value = "...",
    method = RequestMethod.PATCH,
    consumes = "application/json",
    produces = "application/json")
@ResponseBody
public User updateUserPartial(@PathVariable("userId") String userId,
                                  @RequestBody Map<String, Object> userMap,
                                  @RequestBody User user,
                                  HttpServletResponse response) {
...
}