知识点就不多说了，网上一大堆，写了例子加深记忆
<%@ 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>
</head>
<script type="text/javascript">
var xmlHttp=null;
//创建xmlhttprequest对象
if(window.XMLHttpRequest){
xmlHttp=new XMLHttpRequest();
}else{
xmlHttp=new ActiveObject("Microsoft.XMLHTTP");
}
function myclick(){
//创建连接
xmlHttp.onreadystatechange=checkstat;
var url="Myservlet";
xmlHttp.open("post",url,true);
//OPEN方法：第一参数：提交方式，第二参数：URL地址，第三参数：是否异步交互
xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
//发送请求
xmlHttp.send();
//等待响应
}
//处理响应
function checkstat(){
if(xmlHttp.readyState==4){//信息处理完毕，响应信息已经返回给处理器
if(xmlHttp.status==200){
//接收服务器返回的xml数据
alert(xmlHttp.responseText);
var xmlFile=xmlHttp.responseXML;
var java=xmlFile.getElementsByTagName("java");
var javaname=java[0].getAttribute("name");
alert("java name的属性值"+javaname);
//获取根节点下面的所有子节点
var classes=java[0].childNodes;
alert("长度:"+classes.length);
var classname=classes[0].childNodes[0].text;
alert("classname:"+classname);
for(var i=0;i<classes.length;i++){
for(var m=0;m<classes[i].childNodes.length;m++){
var t=classes[i].childNodes[m].text;
}
}
}
}
}
</script>
<body>
<input type="button" onclick="myclick()" value="click" />
</body>
</html>
servlet代码：
public void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException {
PrintWriter out = response.getWriter();
response.setContentType("text/xml");
response.setCharacterEncoding("utf-8");
out.println("<?xml version='1.0' encoding='UTF-8'?>");
//out.println("<?xml version="+"1.0"+" "+"encoding="+"UTF-8"+"?>");
out.println("<java name='java1302'>");
out.println("<classes>");
out.println(" <name>ajax</name>");
out.println("</classes>");
out.println("<classes>");
out.println(" <name>java</name>");
out.println("</classes>");
out.println("<classes>");
out.println(" <name>oracle</name>");
out.println("</classes>");
out.println("</java>");
out.flush();
out.close();
}