Ajax Servlet
//main.jsp<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%><!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>xmlhttp请求Java Servlet</title></head><script type="text/javascript" language="javascript">function createXmlRequest(){var xmlreq=false;if(window.XMLHttpRequest){xmlreq=new XMLHttpRequest();}else if(window.ActiveXObject){try{xmlreq=new ActiveXObject("Msxml2.XMLHTTP");}catch(e1){try{xmlreq=new ActiveXObject("Microsoft.XMLHTTP");}catch(e2){}}}return xmlreq;}function userNameCheck(){var username=document.all.username.value;var request=createXmlRequest();alert(username);alert("上面这是页面的值");request.open("post","UserAction?username="+username);alert(username);request.send();request.onreadystatechange=function(){if(request.readyState==4)if(request.status==200){var value=request.responseText;alert("传回java段验证的值");alert(value);if(value=="true"){document.all.unc.innerHTML="该用户名已存在";}else{document.all.unc.innerHTML="OK";}}}}</script><body>用户姓名：<input type="text" name="username" /><font color="red" size="-1" id="unc"></font></body></html>
//UserAction
package com.java.page;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 UserAction extends HttpServlet{public UserAction(){super();}protected void doGet(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException{this.doPost(request, response);}protected void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException{response.setContentType("text/html");response.setCharacterEncoding("utf-8");String username=request.getParameter("username");//if("abin".equals(username)){if(username.equals("abin")){response.getWriter().print("true");//response.getWriter().write(true);}else{//response.getWriter().print(false);response.getWriter().print("false");}}}
//web.xml
<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <servlet> <servlet-name>UserAction</servlet-name> <servlet-class>com.java.page.UserAction</servlet-class> </servlet><servlet-mapping><servlet-name>UserAction</servlet-name><url-pattern>/UserAction</url-pattern></servlet-mapping><welcome-file-list> <welcome-file>index.jsp</welcome-file></welcome-file-list></web-app>
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