重点：理解Ajax原理，几大步骤：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'ajax.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">
function createXHR(){ //创建XMLHttpRequest对象
try{
//alert(1);
return new ActiveXObject('Msxml2.xmlhttp');
}catch(e){
//alert(2);
return new XMLHttpRequest();
}
}
//createXHR()
function checkuserexist(){
var username=document.getElementById('userform').username.value;
//alert(username);
var xhr=createXHR();
xhr.onreadystatechange=function(){ //注册处理函数
if(xhr.readyState==4){
// 服务器响应正确（当服务器响应正确时，返回值为200的状态码）
if (xhr.status == 200)
{
var msg=xhr.responseText; //处理响应
document.getElementById('usermsg').innerHTML='<span style="color:reg">'+msg+'<span>'
}
}
}
//建立连接
xhr.open('GET','index.jsp?u='+username,true);
//发送请求
xhr.send(null);
//处理响应
// xhr.responseText;
}
</script>
</head>
<body>
<form id='userform'>
请填写用户名:<input type='text' name='username',id='username' onblur='checkuserexist();'/>
<div id='usermsg'></div>
</form>
</body>
</html>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
response.setCharacterEncoding("utf-8");
String name=request.getParameter("u");
if(name.equals("abc")){
out.println("存在");
}else{
out.println("不存在");
}
out.println("jioijjioj");
out.flush();
%>
结果：
原文链接：https://www.f2er.com/ajax/164719.html
