The request sent by the client was syntactically incorrect. 400 问题

@RequestMapping(value = "/login/signin", method = RequestMethod.POST)
    public @ResponseBody Person login(HttpServletRequest request, @RequestBody Person person){
 //...       
}

public class Person {
 private int id;
 private String name;      

 //... set get
}

function init() {
      var url = "login/signin";
      var req = new Object();
　　　 req.id = 1;
      req.name = "aaa";
      req.age = 18;  // Person 没有age 属性.
      (function() {
          $.ajax({
                type : ‘post‘,
                url : url,
                contentType : ‘application/json‘,
                datatype : ‘json‘,
                data : JSON.stringify(req),
                success : processSuccess,
                error : processError
              });
      })();
      function processSuccess(result) {
          alert("success--"+result);
      }
      function processError(result) {
          alert("error--"+result);
      }
  }