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

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);
    }
}

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, IE5
        xhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }

向服务器发送请求

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

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

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 instanceof FormData}function s(e){var t;return t="undefined"!=typeof ArrayBuffer&&ArrayBuffer.isView?ArrayBuffer.isView(e):e&&e.buffer&&e.buffer instanceof ArrayBuffer}function u(e){return"string"==typeof e}function a(e){return"number"==typeof e}function c(e){return"undefined"==typeof e}function f(e){return null!==e&&"object"==typeof e}function p(e){return"[object Date]"===R.call(e)}function d(e){return"[object File]"===R.call(e)}function l(e){return"[object Blob]"===R.call(e)}function h(e){return"[object Function]"===R.call(e)}function m(e){return f(e)&&h(e.pipe)}function y(e){return"undefined"!=typeof URLSearchParams&&e instanceof URLSearchParams}function w(e){return e.replace(/^\s*/,"").replace(/\s*$/,"")}function g(){return("undefined"==typeof navigator||"ReactNative"!==navigator.product)&&("undefined"!=typeof window&&"undefined"!=typeof document)}function v(e,t){if(null!==e&&"undefined"!=typeof e)if("object"!=typeof e&&(e=[e]),r(e))for(var n=0,o=e.length;n<o;n++)t.call(null,e[n],n,e);else for(var i in e)Object.prototype.hasOwnProperty.call(e,i)&&t.call(null,e[i],i,e)}function x(){function e(e,n){"object"==typeof t[n]&&"object"==typeof e?t[n]=x(t[n],e):t[n]=e}for(var t={},n=0,r=arguments.length;n<r;n++)v(arguments[n],e);return t}function b(e,t,n){return v(t,function(t,r){n&&"function"==typeof t?e[r]=E(t,n):e[r]=t}),e}var E=n(3),C=n(4),R=Object.prototype.toString;e.exports={isArray:r,isArrayBuffer:o,isBuffer:C,isFormData:i,isArrayBufferView:s,isString:u,isNumber:a,isObject:f,isUndefined:c,isDate:p,isFile:d,isBlob:l,isFunction:h,isStream:m,isURLSearchParams:y,isStandardBrowserEnv:g,forEach:v,merge:x,extend:b,trim:w}},function(e,t){"use strict";e.exports=function(e,t){return function(){for(var n=new Array(arguments.length),r=0;r<n.length;r++)n[r]=arguments[r];return e.apply(t,n)}}},function(e,t){function n(e){return!!e.constructor&&"function"==typeof e.constructor.isBuffer&&e.constructor.isBuffer(e)}function r(e){return"function"==typeof e.readFloatLE&&"function"==typeof e.slice&&n(e.slice(0,0))}/*!
 * Determine if an object is a Buffer
 *
 * @author   Feross Aboukhadijeh <https://feross.org>
 * @license  MIT
 */
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//# sourceMappingURL=axios.min.map

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

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

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

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。

导入坐标

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

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;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

Java对象转JSON字符串

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);
    }
}