实验八 会话管理一、实验目的1. 了解Web服务器对客户跟踪的各种方法；2. 重点掌握使用HttpSession对象跟踪会话的方法； 3. 掌握使用Cookie技术跟踪会话的方法；4. 了解URL重写和隐藏表单域的方法。二、实验原理HTTP协议是无状态的协议。在很多情况下，Web服务器必须能够跟踪客户的状态。比如，对于一个购物网站，在一个时刻可能有多个客户购物，Web服务器必须能够区分不同的客户。一般情况下，Web服务器为每个客户配置了虚拟的购物车（ShoppingCart）。当某个客户请求将一个商品放入购物车时，Web服务器必须根据发出请求的客户的身份，找到该客户的购物车，然后把商品放入其中。Web服务器跟踪客户的状态通常有4种方法：（1）使用HttpSession对象管理会话；（2）使用持久的Cookie对象；（3）使用URL重写机制；（4）使用隐藏的表单域。三、实验内容与步骤（一） 使用HttpSession对象管理会话。package com.demo;import java.io.*;import javax.servlet.*;import javax.servlet.http.*;import java.util.Date;public class ShowSession extends HttpServlet public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException response.setContentType(text/html); HttpSession session = request.getSession(); String heading =null; Integer accessCount = (Integer)session.getAttribute(accessCount); if(accessCount=null) accessCount = new Integer(0); heading = Welcome, Newcomer; else heading = Welcome Back.; accessCount = new Integer(accessCount.intValue()+1); session.setAttribute(accessCount,accessCount); PrintWriter out = response.getWriter(); out.println(); out.println(Session Tracking Example); out.println(); out.println(+heading+); out.println(Information about your session.); out.println(); out.println(Info TypeValuen); out.println(ID+session.getId()+n); out.println(Creation Time:); out.println(+new Date(session.getCreationTime()+n); out.println(Time of last access:); out.println(+new Date(session.getLastAccessedTime()+n); out.println(Access number:+accessCount+n); out.println(); ShowSession程序的运行结果（二）使用Cookie跟踪会话使用Cookie跟踪会话涉及到向客户端写入Cookie和从客户端读取Cookie。【步骤1】向客户端写入Cookie对象package test;import java.io.*;import javax.servlet.*;import javax.servlet.http.*;public class SendCookie extends HttpServlet public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException,ServletException Cookie userCookie = new Cookie(user, uid1234); userCookie. setMaxAge(60*60*24*7); response.addCookie(userCookie); response.setContentType(text/html);PrintWriter out=response.getWriter();out.println(add cookies);out.println(+A cookie has been sent to brower);out.println(); 访问上述Servlet将向客户端写入一个Cookie，执行后可查看客户机对应目录看是否写了一个文件。SendCookie程序的运行结果【步骤2】从客户端读取Cookie对象package test;import java.io.*;import javax.servlet.*;import javax.servlet.http.*;public class GetCookie extends HttpServlet public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException,ServletException String cookieName = user; String cookieValue = null; Cookie cookies = request.getCookies(); if (cookies!=null) for(int i = 0;icookies.length;i+) Cookie cookie = cookiesi; if(cookie.getName().equals(cookieName) cookieValue = cookie.getValue(); response.setContentType(text/html);PrintWriter out=response.getWriter();out.println(get cookies);out.println(A cookie has been got from brower);out.println(CookieName:+cookieName+);out.println(CookieValue:+cookieValue+);out.println(); GetCookie程序的运行结果四、思考题1. 简述会话管理的常用方法有哪些？ 2. 如何使用HttpSession对象共享数据？