整个界面为chat.jsp：
如果用户没有登录，就不能进行聊天。
为将发言的句子传到页面上，要设置一个<iframe></iframe>虚拟框架，将allmessage.jsp的内容转过来
而allmessage.jsp里的内容是通过application获取发言的内容。点击“发言”，会调用chat.do的servlet，
使用重定向可以将application传到allmessage.jsp
chat.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>直播室</title>
<style>
#main #allmsg{border:solid 1px #ccc; height:400px;}
#main #mymsg input[type=text]{width:800px; height:30px; }
#main #mymsg input[type=submit]{width:80px; height:36px;
font-size:20px; vertical-algin:middle; line-height:30px;}
</style>
<script>
function Clear(){
var frm = document.getElementById("form1");
var obj = document.getElementById("msg");
frm.submit();
obj.value = "";
return false
}
</script>
</head>
<body>
<jsp:include page = "head.jsp?col=4"></jsp:include>
<div id="main" class="layout">
<div id="allmsg">
<iframe src="allmessage.jsp" width="1000" height="400" name="f1" frameborder="0"></iframe>
</div>
<%
String user = (String)session.getAttribute("username");
if(user!=null){
%>
<div id="mymsg">
<form id="form1" action="chat.do" method="post" target="f1" onsubmit="return Clear();">
<input type="text" id="msg" name="message">
<input type="submit" value="发言">
</form>
</div>
<%
}
%>
</div>
<%@ include file="foot.jsp" %>
</body>
</html>
ChatServlet doGet
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//获取表单数据
request.setCharacterEncoding("utf-8");
String msg = request.getParameter("message");
System.out.println(msg);
//获取session
HttpSession session = request.getSession();
String user = (String)session.getAttribute("username");
//加入application
ServletContext application = this.getServletContext();
String allmsg = (String)application.getAttribute("chat");
if(allmsg == null) {
allmsg = "["+Tools.getTime()+"]"+ user + "说：" + msg + "<br>";
}else {
allmsg += "["+Tools.getTime()+"]"+ user + "说：" + msg + "<br>";
}
application.setAttribute("chat", allmsg);
System.out.println(allmsg);
// 重定向
response.sendRedirect("allmessage.jsp");
}
获取时间用这个
