1.java代码如下:
 package com.eduask;
 import java.io.IOException;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 //测试Ajax请求方式为post;
 public class Demo3 extends HttpServlet{
 @Override
 protected void service(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 req.setCharacterEncoding("utf-8");
 resp.setCharacterEncoding("utf-8");
 resp.setContentType("text/html;charset=utf-8");
 //接受用户的输入的name;
 String name=req.getParameter("name1");
 if("tom".equals(name)){
 resp.getWriter().write("<font color=red>该用户已经注册</font>");
 }else{
 resp.getWriter().write("<font color=blue>用户可以注册</font>");
 }
 }
 }
 2.demo3.jsp代码如下:
 <%@ page language="java" contentType="text/html; utf-8"
 pageEncoding="utf-8"%>
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 <title>ajax测试post请求方式</title>
 </head>
 <body>
 请输入用户名: <input id="name1" type="text" name="name1">
 <span id="span1"></span>
 <script type="text/javascript">
 var getName1Id=document.getElementById("name1");
 getName1Id.οnblur=function(){
 var xhr=getXhr();
 xhr.onreadystatechange=function(){
 if(xhr.readyState==4){
 if(xhr.status==200){
 var msg=xhr.responseText;
 var span1=document.getElementById("span1");
 span1.innerHTML=msg;
 }
 }
 }
 xhr.open("post","/ajax/Demo3");
 //设置消息头，告诉浏览器携带请求体数据;
 xhr.setRequestHeader("content-type","application/x-www-form-urlencoded");
 xhr.send("name1="+getName1Id.value);
 }
 function getXhr(){
 var xhr;
 if(window.XMLHttpRequest){
 xhr=new XMLHttpRequest();
 }else{
 xhr=new ActiveXObject("microsoft,xmlhttp");
 }
 return xhr;
 }
 </script>
 </body>
 </html>
 3.web.xml配置文件如下:
 <!-- demo3 -->
 <servlet>
 <servlet-name>Demo3</servlet-name>
 <servlet-class>com.eduask.Demo3</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>Demo3</servlet-name>
 <url-pattern>/Demo3</url-pattern>
 </servlet-mapping>