一、Web 2.0的特点
提到Ajax不得不提到WEB2.0
1、用户贡献内容
2、内容聚合RSS
3、更丰富的“用户体验”
二、Ajax的作用
无刷新：不刷新整个页面，只刷新局部
无刷新的好处
只更新部分页面，有效利用带宽
提供连续的用户体验
提供类似C/S的交互效果，操作更方
三、传统Web与Ajax的差异
四、Ajax简介
1、Ajax：异步刷新技术
2、Ajax工作流程
3、Ajax技术的核心-XMLHttpRequest提供异步发送请求的能力
3.1常用方法
3.2常用属性
readystate：XMLHttpRequest的状态信息
onreadystatechange：指定回调函数
status：HTTP的状态码
statusText ：返回当前请求的响应状态
responseText：获得响应的文本内容
responseXML：获得响应的XML文档对象
五、功能实现
index.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>注册</title>
</head>
<script type="text/javascript">
var xmlHttpRequest;
function validate(){
var uname = document.getElementById("uname").value;
if(uname==null || uname==""){
document.getElementById("unameDiv").innerText = "用户名不能为空！";
}else{
//1.创建XMLHttpRequest对象
xmlHttpRequest = createXmlHttpRequest();
//2.设置回调函数
xmlHttpRequest.onreadystatechange = callBack;
//3.初始化XMLHttpRequest组件
var url = "CheckNameServlet";
xmlHttpRequest.open("post",url,true);//get方式
xmlHttpRequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
//4.发送请求
var data="uname="+uname;//需要发送的数据信息，name为用户名输入框获取的值
xmlHttpRequest.send(data);
}
} /*
*创建XMLHttpRequest对象
*/
function createXmlHttpRequest(){
if(window.XMLHttpRequest){
return new XMLHttpRequest();
}else{//返回值为false时说明是老版本IE浏览器（IE5和IE6）
return new ActiveXObject("Microsoft.XMLHTTP");
}
} //Ajax 回调函数
function callBack(){
if(xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200){
var data = xmlHttpRequest.responseText;
if(data == "true"){
document.getElementById("unameDiv").innerText = "用户名已被使用！";
}else{
document.getElementById("unameDiv").innerText = "用户名可以使用！";
}
}
}
</script>
<body>
<form action="" id="form1" >
<table>
<tr>
<td>用 户 名：</td>
<td>
<input type="text" name="uname" id="uname" onblur="validate();" /> <font color="#c00fff">*</font>
</td>
<td>
<div id="unameDiv" style="display: inline"></div>
</td>
</tr>
</table>
</form>
</body>
</html>
CheckNameServlet
package com.qj.servlet; import java.io.IOException;
import java.io.PrintWriter; import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; /**
* Servlet implementation class CheckNameServlet
*/
@WebServlet("/CheckNameServlet")
public class CheckNameServlet extends HttpServlet {
private static final long serialVersionUID = 1L; /**
* @see HttpServlet#HttpServlet()
*/
public CheckNameServlet() {
super();
// TODO Auto-generated constructor stub
} /**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String uname = request.getParameter("uname");
System.out.println(uname);
PrintWriter out = response.getWriter();
if("admin".equals(uname)){
out.print("true");
}else{
out.print("false");
}
} /**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
} }