1.Session作用类似于购物车，第一次，放入物品，可以获得Session的id，并可以设置id失效的时间，这样便于多次将物品放在购物车里面，使用的就是获取的Session的id；
2.Session的常用方法：sessionid,获取首次访问的id值，及在jsp页面直接的跳转，这个是login.jsp页面
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
SessionID: <%= session.getId() %>
<br><br> IsNew: <%= session.isNew() %>
<br><br> MaxInactiveInterval: <%= session.getMaxInactiveInterval() %>
<br><br> CreateTime: <%= session.getCreationTime() %>
<br><br> LastAccessTime: <%= session.getLastAccessedTime() %>
<br><br> <%
Object username = session.getAttribute("username");
if(username == null){
username = "";
}
%> <form action="<%= response.encodeURL("hello.jsp") %>" method="post"> username: <input type="text" name="username"
value="<%= username %>"/>
<input type="submit" value="Submit"/> </form>
</body>
</html>
3.hello.jsp页面，有注销和重新登陆的功能，点击注销跳转到logout.jsp页面，有实现注销session的方法，点击重新登陆返回到login页面
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body> SessionID: <%= session.getId() %>
<br><br> IsNew: <%= session.isNew() %>
<br><br> MaxInactiveInterval: <%= session.getMaxInactiveInterval() %>
<br><br> CreateTime: <%= session.getCreationTime() %>
<br><br> LastAccessTime: <%= session.getLastAccessedTime() %>
<br><br> Hello: <%= request.getParameter("username") %>
<br><br> <%
session.setAttribute("username", request.getParameter("username"));
%> <a href="<%= response.encodeURL("login.jsp") %>">重新登录</a>
<a href="<%= response.encodeURL("logout.jsp") %>">注销</a>
</body>
</html>
4.logout.jsp页面：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
SessionID: <%= session.getId() %>
<br><br> IsNew: <%= session.isNew() %>
<br><br> MaxInactiveInterval: <%= session.getMaxInactiveInterval() %>
<br><br> CreateTime: <%= session.getCreationTime() %>
<br><br> LastAccessTime: <%= session.getLastAccessedTime() %>
<br><br> Bye: <%= session.getAttribute("username") %>
<br><br> <a href="login.jsp">重新登录</a> <%
session.invalidate();
%>
</body>
</html>