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                        /JAVA遇見HTML——JSP篇

求大大解答，為什么我兩個頁面session id不一樣，第二個頁面用戶名也是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內置對象</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創建時間：<%=sdf.format(d)?%><br>
?????Session的ID編號：<%=session.getId()%><br>
?????從Session中獲取用戶名：<%=session.getAttribute("username")?%><br>
?????<a?href="session_page2.jsp"?target="_blank">跳轉到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內置對象</h1>
????<hr>
????????Session的ID編號：<%=session.getId()%><br>
?????從Session中獲取用戶名：<%=session.getAttribute("username")?%>
??</body>
</html>

而且每次刷新，ID都不一樣

代碼和老師的一模一樣，應該沒問題