Ajax是创建快速动态网页的技术，通过后台与服务器少量的数据交互，是网页实现异步更新。也就是在不整个刷新页面的情况下，可以更新网页中的局部区域。
在原始web应用的模式中：
浏览器 以 http的形式向服务器发送请求，然后服务器处理请求，然后以响应（HTML+CSS）数据返回给客户端；
AJXA应用中：
浏览器 以http发送的请求到达AJAX引擎，由Ajax向服务器进行请求发送数据，处理完成后，把数据继续返回给Ajax引擎，再以ＸＭＬ或者字符串数据，返回给浏览器；
ajax.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>My JSP 'ajax.jsp' starting page</title> <script type="text/javascript"> //声明一个空对象接受XMLHttpRequest var xmlHttpRequest = null; function ajaxSubmit() {//IE浏览器 if(window.ActiveXObject) { xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP"); } else if(window.XMLHttpRequest) {//其他浏览器 xmlHttpRequest = new XMLHttpRequest(); } if( null != xmlHttpRequest ) {//发送请求 xmlHttpRequest.open("GET","servlet/AjaxServlet",true);//以GET方式向服务发送异步请求 xmlHttpRequest.onreadystatechange = ajaxCallBack; //准备接受 xmlHttpRequest.send(null); //发送请求 } } function ajaxCallBack() { //接受响应 if(xmlHttpRequest.readyState == 4)//等于4说明服务器向客户端已发送了数据 { if(xmlHttpRequest.status == 200)//说明发送的数据服务器没有报任何异常 { var responseText = xmlHttpRequest.responseText; //以Text的形式解析 document.getElementById("div1").innerHTML = responseText; //插入到HTML文档中 } } } </script> </head> <body> <input type="button" value="get content from serve" οnclick="ajaxSubmit()"/> <div id="div1"></div> </body>
</html>
AjaxServlet.java
import java.io.IOException;
import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class AjaxServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); System.out.println("doGet invoked"); out.println("Hello World AJAX"); out.flush(); out.close(); } } web.xml<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"><servlet>
<description>This is the description of my J2EE component</description> <display-name>This is the display name of my J2EE component</display-name> <servlet-name>AjaxServlet</servlet-name> <servlet-class>com.zhaoming.shopping.servlet.AjaxServlet</servlet-class> </servlet><servlet-mapping>
<servlet-name>AjaxServlet</servlet-name> <url-pattern>/servlet/AjaxServlet</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>Index.jsp</welcome-file> <welcome-file>index.html</welcome-file> </welcome-file-list>