求大大解答，为什么我两个页面session id不一样 ，第二个页面用户名也是null
<%@ page language="java" import="java.util.*,java.text.*" contentType="text/html; charset=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 'index.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">
-->
</head>
<body>
<h1>session内置对象</h1>
<hr>
<%
SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
Date d = new Date(session.getCreationTime());
session.setAttribute("username","admin") ;
%>
Session创建时间：<%=sdf.format(d) %><br>
Session的ID编号：<%=session.getId()%><br>
从Session中获取用户名：<%=session.getAttribute("username") %><br>
<a href="session_page2.jsp" target="_blank">跳转到Session_page2.jsp</a>
</body>
</html><%@ page language="java" import="java.util.*,java.text.*" contentType="text/html; charset=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 'index.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">
-->
</head>
<body>
<h1>session内置对象</h1>
<hr>
Session的ID编号：<%=session.getId()%><br>
从Session中获取用户名：<%=session.getAttribute("username") %>
</body>
</html>而且每次刷新，ID都不一样
代码和老师的一模一样，应该没问题
