Ajax-Demo

index.jsp 
1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 4 <html>
 5 <head>
 6 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 7 <title>Insert title here</title>
 8 <script type="text/javascript">
 9     window.onload=function(){
10         //1.获取a节点，并对其添加onclick响就函数
11         document.getElementsByTagName("a")[0].onclick=function(){
12             //3.创建一个XMLHttpRequest对象
13             var request=new XMLHttpRequest();
14             //4.准备发送请求的数url,加上时间戳
15             var url=this.href +"?time=" + new Date();
16             var method="GET";
17             //5.调用XMLHttpRequest的open方法
18             request.open(method,url);
19             //6.调用XMLHttpRequest的send方法
20             request.send(null);
21             //7.为XMLHttpRequest对象添加onreadystatechange响应函数
22             request.onreadystatechange = function(){
23                 //8.判断响应是否完成：XMLHttpRequest对象的readyState属性为4的时侯
24                 if(request.readyState == 4){
25                     //9.再判断响应是否可用：XMLHttpRequest对象status属性值为200
26                     if(request.status == 200||request.status == 304){
27                         //10.打印响 应结果：reponseText
28                         alert("aaa")
29                         alert(request.responseText);
30                     }
31                 }
32             }
33             //2.取消a节点默认行为
34             return false;
35         }
36     }
37 </script>
38 </head>
39 <body>
40 <a href="test.txt">test helloWord!</a>
41 </body>
42 </html>

test.txt 
hello world,the first ajax!