| 发表于：2007-05-12 10:47:264楼 得分:0 |
ajax 可以实现，如下所示：
login.jsp
<%@ page contenttype= "text/html;charset=gb2312 " language= "java " %>
<head>
<meta http-equiv=content-type content= "text/html; charset=gb2312 ">
<style>
span{
color:red;
font-size:12px;
text-indent:2em;
}
</style>
</head>
<script language= "javascript ">
var xmlhttpreq = false;
//创建xmlhttprequest对象
function createxmlhttprequest（) {
if（window.xmlhttprequest) { //mozilla 浏览器
xmlhttpreq = new xmlhttprequest（);
}
else if （window.activexobject) { // ie浏览器
try {
xmlhttpreq = new activexobject（ "msxml2.xmlhttp ");
} catch （e) {
try {
xmlhttpreq = new activexobject（ "microsoft.xmlhttp ");
} catch （e) {}
}
}
}
//发送请求函数
function sendrequest（url) {
createxmlhttprequest（);
xmlhttpreq.open（ "get ", url, true);
xmlhttpreq.onreadystatechange = processresponse;//指定响应函数
xmlhttpreq.send（null); // 发送请求
}
// 处理返回信息函数
function processresponse（) {
if （xmlhttpreq.readystate == 4) { // 判断对象状态
if （xmlhttpreq.status == 200) { // 信息已经成功返回，开始处理信息
var res=xmlhttpreq.responsexml.getelementsbytagname（ "res ")[0].firstchild.data;
document.getelementbyid（ "cn ").innerhtml=res;
}
}
}
// 身份验证函数
function checkusername（) {
var username=document.getelementbyid（ "username ").value;
var url= "checkusername?username= "+ username;
sendrequest（url);
}
</script>
<body vlink= "#006666 " link= "#003366 " bgcolor= "#e0f0f8 ">
<form action= " " method= "post " name= "form ">
用户名： <input size= "15 " type= "text " name= "username "onblur= "checkusername（) " onkeypress= "checkusername（) " onkeyup= "checkusername（) " onkeydown= "checkusername（) " />
<span id= "cn "> </span> <p>
密 码： <input type= "password " size= "15 " name= "psw "> <p>
<input type= "button " value= "登录 " onclick= "checkusername（) " >
</form>
checkusername.java
package com.sum;
import java.io.ioexception;
import java.io.printwriter;
import javax.servlet.servletconfig;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
public class checkusername extends httpservlet {
public void init（servletconfig config) throws servletexception {
}
/*
* 处理 <get> 请求方法.
*/
protected void doget（httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
//设置接收信息的字符集
request.setcharacterencoding（ "utf-8 ");
//接收浏览器端提交的信息
string username = request.getparameter（ "username ");
//设置输出信息的格式及字符集
response.setcontenttype（ "text/xml; charset=utf-8 ");
response.setheader（ "cache-control ", "no-cache ");
//创建输出流对象
printwriter out = response.getwriter（);
//依据验证结果输出不同的数据信息
out.println（ " <response> ");
if（username.equals（ "jenny ")){
out.println（ " <res> " + "热烈的欢迎您! " + " </res> ");
}else{
out.println（ " <res> " + "对不起,登录失败！ " + " </res> ");
}
out.println（ " </response> ");
out.close（);
}
/*
* 处理 <post> 请求方法.
*/
protected void dopost（httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
doget（request, response);
}
}
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