1.post请求,默认传输格式application/x-www-form-urlencoded，data是对象，使用键值对，传输复杂数据

var y={
    id:5,
    name: "张三",
    city:"上海",
}
var x={
    sex:'男',
    user:y,
};
$("#aaa").click(function () {
    $.post({
        url:'/hello/aaa',
        //contentType:"application/json;charset=utf-8",
        data:{obj:JSON.stringify(x)},
        success:function(data){
            alert(data);
        }
    });
});

后台接收

public User aaa(String obj){
    JSONObject jobj=JSON.parseObject(obj);
    String sex=jobj.getString("sex");
    String user1=jobj.getString("user");
    User user=JSON.parseObject(user1,User.class);
    return user;
}

2.post请求contentType:"application/json;charset=utf-8",data必须是json字符串,后台接收要加@RequestBody，传输复杂数据

var y={
    id:5,
    name: "张三",
    city:"上海",
}
var x={
    sex:'男',
    user:y,
};
$("#aaa").click(function () {
    $.post({
        url:'/hello/aaa',
        contentType:"application/json;charset=utf-8",
        data:JSON.stringify(x),
        success:function(data){
            alert(data);
        }
    });
});

后台接收

(1)

public User aaa(@RequestBody String obj){
        JSONObject jobj=JSON.parseObject(obj);
        String sex=jobj.getString("sex");
        String user1=jobj.getString("user");
        User user=JSON.parseObject(user1,User.class);
        return user;
    }

(2)

public User aaa(@RequestBody Map<String,Object> ma){
        String sex=ma.get("sex").toString();
        Map<String,Object> ma1=(Map<String,Object>)ma.get("user");
        String s=JSON.toJSONString(ma1);            //map转json字符串
        User user=JSON.parseObject(s,User.class);   //json字符串转实体类
        return user;
}

总而言之就是：如果没加contentType:"application/json"，那么data就应该对应的是对象；反之，如果加了contentType:"application/json"，那么ajax发送的就必须是字符串。

https://www.cnblogs.com/xiaozong/p/5732332.html