jquery-3.5.1.js
get  , post  ,post json 例子

ajax几个重要参数
// 默认 get
type: "post"

// contentType 默认 application/x-www-form-urlencoded
contentType: "application/json; charset=utf-8",
// 默认 true ,异步请求
async: false,

post json 时
data 数据一定要转成 json string 
data: JSON.stringify(user3),


服务端 rest 接口
@RequestMapping("/getUser")
public User getUser(User user){
    return user;
}
	
@RequestMapping("/getUserFromJson")
public User getUserFromJson(@RequestBody User user){
    return user;
}
            


function getData() {
        // alert('hello2');
        var user = { "id": 9, "name": "tiger" };
        alert('hello,' + JSON.stringify(user));

        // ajax get
        $.ajax({
            url: "/data/getUser",
            data: user,
            success: function (data) {
                console.log(data);
                $('#data1').html(JSON.stringify(data));
            }
        });

        // ajax post
        var user2 = { "id": 9, "name": "tiger2" };
        $.ajax({
            type: "post",
            url: "/data/getUser",
            data: user2,
            success: function (data) {
                console.log(data);
                $('#data2').html(JSON.stringify(data));
            }
        });
        // ajax post json 
        var user3 = { "id": 9, "name": "tiger3" };

        $.ajax({
            // 默认 get
            type: "post",
            // contentType 默认 application/x-www-form-urlencoded
            contentType: "application/json; charset=utf-8",
            //  预期的服务器响应的数据类型 ,可以不写
            // dataType: "json", 
            url: "/data/getUserFromJson",
            // 一定要转成string
            data: JSON.stringify(user3),
            // data:user3,
            success: function (data) {
                console.log(data);
                $('#data3').html(JSON.stringify(data));
            }
        });
    }
    
 

 完整代码
 
 https://gitee.com/dyyx/springboothello/blob/master/src/main/resources/static/jquery_ajax_post.html
 
 https://gitee.com/dyyx/springboothello/blob/master/src/main/java/demo/controller/DataBindController.java