页面：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'ajax3.jsp' starting page</title>
<Meta http-equiv="pragma" content="no-cache">
<Meta http-equiv="cache-control" content="no-cache">
<Meta http-equiv="expires" content="0">
<Meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<Meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<script type="text/javascript">
//创建异步对象
function createXMLHttpRequest() {
try {
return new XMLHttpRequest();//大多数浏览器
} catch (e) {
try {
return ActvieXObject("Msxml2.XMLHTTP");//IE6.0
} catch (e) {
try {
return ActvieXObject("Microsoft.XMLHTTP");//IE5.5及更早版本
} catch (e) {
alert("您的浏览器不支持");
throw e;
}
}
}
}
window.onload = function() {
// 获取文本框，给它的失去焦点事件注册监听
var userEle = document.getElementById("usernameEle");
userEle.onblur = function() {
//1.得到异步对象
var xmlHttp = createXMLHttpRequest();
//2.打开连接
//xmlHttp.open("POST","<c:url value='/ValidateUsernameServlet'/>",true);
xmlHttp.open("POST","/Web/ValidateUsernameServlet",true);
//3.设置请求头：Content-Type
xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
//4.发送请求，给出请求体
xmlHttp.send("username=" + userEle.value);
//5.给xmlHttp的onreadystatechange事件注册监听
xmlHttp.onreadystatechange = function() {
if(xmlHttp.readyState == 4 && xmlHttp.status == 200) {//双重判断
//获取服务器的响应，判断是否为1
// 是：获取span，添加内容：“用户名已被注册”
var text = xmlHttp.responseText;
var span = document.getElementById("errorSpan");
if(text == "1") {
//得到span元素
span.innerHTML = "用户名已被注册！";
} else {
span.innerHTML = "";
}
}
};
};
};
</script>
</head>
<body>
<h1>演示用户名是否被注册</h1>
<form action="" method="post">
用户名：<input type="text" name="username" id="usernameEle"/><span id="errorSpan"></span><br/>
密 码：<input type="password" name="password"/><br/>
<input type="submit" value="注册"/>
</form>
</body>
</html>
ValidateUsernameServlet
package com.java.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ValidateUsernameServlet extends HttpServlet {
protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html; charset=utf-8");
String username = request.getParameter("username");
if(username.equals("itachi")) {
response.getWriter().print("1");
} else {
response.getWriter().print("0");
}
}
}