AJAX登陆实例!

index.jsp文件:
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<html>
  <head>
  <script>
 	//设一个变量	
 	var XMLHttpReq=false;
 		//创建一个XMLHttpRequest对象
 	function createXMLHttpRequest(){
 	       if(window.XMLHttpRequest){ //Mozilla 
 			XMLHttpReq=new XMLHttpRequest();
 		}
 	       else if(window.ActiveXObject){
 		   try{
 		       XMLHttpReq=new ActiveXObject("Msxml2.XMLHTTP");
 		   }catch(e){
		               try{
	   			    XMLHttpReq=new ActiveXObject("Microsoft.XMLHTTP");
			      }catch(e){}
 									}
 								}
 							}
 		//发送请求函数
 	function send(url){
 	         createXMLHttpRequest();
 		XMLHttpReq.open("GET",url,true);
 		XMLHttpReq.onreadystatechange=proce;   //指定响应的函数
 		XMLHttpReq.send(null);  //发送请求
 			}
 	function proce(){
 		if(XMLHttpReq.readyState==4){ //对象状态
 		if(XMLHttpReq.status==200){//信息已成功返回,开始处理信息
 		var res=XMLHttpReq.responseXML.getElementsByTagName("content")[0].firstChild.data;
 		window.alert(res);
 		}else{
 			window.alert("所请求的页面有异常");
 		}
 		}
 	}
 		//身份验证 
 	function check(){
 		var name=document.getElementById("name").value;
		if(name==""){
 			alert("请输入内容");
 			return false;
 			}
 			else{
 				send('login?name='+name);
 				}
 			}
 					
 		</script>
  </head>
  <body>
    <form action="login" method="post">
     	<tr><td>姓名: <input id="name" type="text" name="name"/>
     	 <input type="button" value="检测" onClick="check()"/>
     	</td>
     	</tr>   	
     </form> 	
  </body>
</html>


TestA.java这是一个Servlet文件:
package tt;
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 TestA extends HttpServlet {

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {		
		request.setCharacterEncoding("utf-8");
		String name=request.getParameter("name");
		
		response.setContentType("text/xml; charset=utf-8");
		response.setHeader("Cache-Control","no-cache");
		PrintWriter out=response.getWriter();
		out.println("<pront>");
		if(name.equals("and4walker")){
			out.println("<content>"+"对不起,此名已经注册"+"</content>");
		}else{
			out.println("<content>"+"可以注册"+"</content>");
		}
		out.println("</pront>");
		out.close();
	}

}



web.xml文件:
<?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>
		<servlet-name>login</servlet-name>
		<servlet-class>tt.TestA</servlet-class>
	</servlet>
	
	<servlet-mapping>
		<servlet-name>login</servlet-name>
		<url-pattern>/login</url-pattern>
	</servlet-mapping>
</web-app>

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