原理：简单来说就是利用ajax的异步，ajax每隔一段时间会从后台获取数据而不刷新页面。
isGet表示消息是否被读
2.使用java web做后台，主要使用hibernate和struts2框架，xml数据格式。
3.下面给出核心jsp代码：
friend.jsp:
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%
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>
<base href="<%=basePath%>">
<title>My JSP 'firend.jsp' starting page</title>
<Meta http-equiv="pragma" content="no-cache">
<Meta http-equiv="cache-control" content="no-cache">
<Meta http-equiv="expires" content="0">
<Meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<Meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<script type="text/javascript" src="my.js"></script>
<script type="text/javascript">
function change1(val,obj){
if(val=='over'){
obj.style.color='red';
obj.style.cursor='hand';
}
else if(val=='out'){
obj.style.color='black';
}
}
function openChatRoom(obj){
window.open("${pageContext.request.contextPath}/chat/friend_gotochat.action?username="+encodeURI(obj.innerText),"_blank");
}
</script>
</head>
<body>
<h1>欢迎${user.username }</h1>
<ul>
<c:forEach items="${list}" var="everyuser">
<li onmouSEOver="change1('over',this)" onclick="openChatRoom(this)"
onmouSEOut="change1('out',this)">${everyuser.username }</li>
</c:forEach>
</ul>
</body>
</html>
以上代码的功能只是实现当用户点击好友列表的某个好友时，浏览器打开一个新的聊天界面
chating.jsp:
<%@ 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>
<base href="<%=basePath%>">
<title>My JSP 'chating.jsp' starting page</title>
<Meta http-equiv="pragma" content="no-cache">
<Meta http-equiv="cache-control" content="no-cache">
<Meta http-equiv="expires" content="0">
<Meta http-equiv="keywords" content="keyword1,keyword3">
<Meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<script type="text/javascript" src="my.js"></script>
<script type="text/javascript">
//打开新窗口的大小
window.resizeTo(700,400);
//每隔5秒向后台要数据
window.setInterval("getMessage()",5000);
//向后台要数据的函数
function getMessage(){
var myXmlHttpRequest=getXmlHttpObject();
if(myXmlHttpRequest){
var url="${pageContext.request.contextPath}/chat/chat_backchat.action";
var data="getterid="+'${user.id }'+"&senderid="+'${usertochat.id}';
myXmlHttpRequest.open("post",url,true);
myXmlHttpRequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
myXmlHttpRequest.onreadystatechange=function (){
if(myXmlHttpRequest.readyState==4){
if(myXmlHttpRequest.status==200){
//当数据回来后，将数据显示在指定位置
var meses=myXmlHttpRequest.responseXML;
var contents=meses.getElementsByTagName("content");
var sendtimes=meses.getElementsByTagName("sendtime");
for(var i=0;i<contents.length;i++){
var str='${usertochat.username }'+"："+contents[i].childNodes[0].nodeValue+"\r\n"+sendtimes[i].childNodes[0].nodeValue
$('mycons').value+=str+"\r\n";
}
}
}
}
myXmlHttpRequest.send(data);
}
}
//发送数据的函数
function sendmessage(){
var myXmlHttpRequest=getXmlHttpObject();
if(myXmlHttpRequest){
var url="${pageContext.request.contextPath}/chat/chat_gochat.action";
var data="con="+${'con'}.value+"&getterid="+'${usertochat.id}'+"&senderid="+'${user.id }';
//window.alert(data);
myXmlHttpRequest.open("post","application/x-www-form-urlencoded");
myXmlHttpRequest.onreadystatechange=function (){
if(myXmlHttpRequest.readyState==4){
if(myXmlHttpRequest.status==200){
}
}
}
myXmlHttpRequest.send(data);
$('mycons').value+='${user.username }'+":"+$('con').value+"\r\n"+new Date().toLocaleString()+"\r\n";
$('con').value="";
}
}
</script>
</head>
<body>
<h1>聊天室，<font color="red">${user.username }</font>正在和<font color="red">${usertochat.username }</font>聊天</h1>
<textarea cols="70" rows="10" id="mycons"></textarea><br/>
<input type="text" id="con" style="width:400px"/>
<input type="button" value="发送消息" onclick="sendmessage()"/>
</body>
</html>
my.js:
//创建ajax function getXmlHttpObject(){ var xmlHttpRequest; //XmlHttpObject if(window.ActiveXObject) { //window.alert("ie"); xmlHttpRequest=new ActiveXObject("Microsoft.XMLHTTP"); } else{ //window.alert("ff"); xmlHttpRequest=new XmlHttpRequest(); } return xmlHttpRequest; } //获取id function $(id){ return document.getElementById(id); } //encode"+","&"（对加号和空格编码） function URLencode(sStr) { return escape(sStr).replace(/\+/g,'%2B').replace(/\"/g,'%22').replace(/\'/g,'%27').replace(/\//g,'%2F'); }
