AJAX最简单的原理以及应用

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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" onclick="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>