AJAX,Axios,JSON简单了解

一. AJAX简介

概念: AJAX(Asynchronous JavaScript And XML): 异步的JavaScript 和XML

AJAX作用:

1.与服务器进行数据交换: 通过AJAX可以给服务器发送请求，并获取服务器响应的数据

使用了AJAX和服务器进行通信，就可以使用 HTML+AJAX来替换JSP页面了

2.异步交互:可以在不重新加载整个页面的情况下，与服务器交换数据并更新部分网页的技术，如:搜索联想、用户名是否可用校验，等等...

二. AJAX快速入门

1. 编写AjaxServlet, 并使用response输出字符串

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/ajaxServlet")
public class AjaxServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.getWriter().write("Hello Ajax");}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

2. 创建XMLHttpRequest对象: 用于和服务器交换数据

//创建核心对象var xhttp;if (window.XMLHttpRequest) {xhttp = new XMLHttpRequest();} else {// code for IE6, IE5xhttp = new ActiveXObject("Microsoft.XMLHTTP");}

3. 向服务器发送请求

//发送请求xhttp.open("GET", "http://localhost:8080/ajax-demo/ajaxServlet");xhttp.send();

4. 获取服务器响应数据

xhttp.onreadystatechange = function() {if (this.readyState == 4 && this.status == 200) {document.getElementById("demo").innerHTML =alert(this.responseText)}
};

效果展示

三. Axios快速入门

1. 引入Axios的js文件

/* axios v0.18.0 | (c) 2018 by Matt Zabriskie */
!function(e,t){"object"==typeof exports&&"object"==typeof module?module.exports=t():"function"==typeof define&&define.amd?define([],t):"object"==typeof exports?exports.axios=t():e.axios=t()}(this,function(){return function(e){function t(r){if(n[r])return n[r].exports;var o=n[r]={exports:{},id:r,loaded:!1};return e[r].call(o.exports,o,o.exports,t),o.loaded=!0,o.exports}var n={};return t.m=e,t.c=n,t.p="",t(0)}([function(e,t,n){e.exports=n(1)},function(e,t,n){"use strict";function r(e){var t=new s(e),n=i(s.prototype.request,t);return o.extend(n,s.prototype,t),o.extend(n,t),n}var o=n(2),i=n(3),s=n(5),u=n(6),a=r(u);a.Axios=s,a.create=function(e){return r(o.merge(u,e))},a.Cancel=n(23),a.CancelToken=n(24),a.isCancel=n(20),a.all=function(e){return Promise.all(e)},a.spread=n(25),e.exports=a,e.exports.default=a},function(e,t,n){"use strict";function r(e){return"[object Array]"===R.call(e)}function o(e){return"[object ArrayBuffer]"===R.call(e)}function i(e){return"undefined"!=typeof FormData&&e 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//# sourceMappingURL=axios.min.map

2. 使用Axios发送请求,并获取响应结果

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body><script src="js/axios-0.18.0.js"></script><script>//get/* axios({method:"get",url:"http://localhost:8080/ajax-demo/axiosServlet?username=zhangsan"}).then(function (resp) {alert(resp.data);})*///get简化axios.get("http://localhost:8080/ajax-demo/axiosServlet?username=zhangsan").then(function (resp) {alert(resp.data);})//post/*axios({method:"post",url:"http://localhost:8080/ajax-demo/axiosServlet",data:"username=zhangsan"}).then(function (resp) {alert(resp.data);})*///post简化axios.post("http://localhost:8080/ajax-demo/axiosServlet","username=zhangsan").then(function (resp) {alert(resp.data);})</script></body>
</html>

结果展示

四. JSON

1. 简介

概念: JavaScript Object Notation JavaScript对象表示法

由于语法简单, 层次结构鲜明, 现多用于作为数据载体, 在网络中进行数据传输

2. 基础语法

定义

var 变量名 = {

"key1":value1,

"key2": value2,

"key3":value3

};

var json = {"name":"zhangsan","age": 99,"addr":["北京","天津","广州"]
};

获取数据

变量名.key

json.addr

结果展示

3. JSON数据和Java对象转换

请求数据: JSON字符串转为Java对象

响应数据: Java对象转为JSON字符串

Fastjson是阿里巴巴提供的一个Java语言编写的高性能功能完善的JSON库，是目前Java语言中最快的JSON库，可以实现Java对象和JSON字符串的相互转换。

1. 导入坐标

<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.62</version>
</dependency>

2. 创建一个Java类

public class User {private Integer id;private String username;private String password;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +'}';}
}

3. Java对象转JSON字符串

4. JSON字符串转Java对象

import com.alibaba.fastjson.JSON;
import com.guaiwu.pojo.User;public class JsonDemo {public static void main(String[] args) {//将Java对象转化成json字符串User user = new User();user.setId(1);user.setUsername("lisi");user.setPassword("1234");String jsonString = JSON.toJSONString(user);System.out.println(jsonString);//{"id":1,"password":"1234","username":"lisi"}//将JSON字符串转化成java对象User u = JSON.parseObject("{\"id\":1,\"password\":\"1234\",\"username\":\"lisi\"}", User.class);System.out.println(u);}
}

5. 结果展示