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Session是基于cookie的一种绘画机制，cookie是服务器返回一小份数据到客户端，并且存放在客户端中去，session是将数据存放在服务器端

1.得到session值

HttpSession session = request.getSession(); 2.常用的方法 获取会话的id：session.getId(); 存值 ：session.setAttribute(name,value); 取值：session.getAttribute(name); 移除值：session.removeAttribute(name); 3.session的生命周期 从创建request.getSession()创建开始 从关闭服务器就结束了。一般就只有30分钟的有效期

4.创建一个购物车对象

方法： 1.登录页面

<%@ page language="java" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%>
   
手机一号
手机二号
手机三号
手机四号

2.登陆跳转处理

package com.servlet;import java.io.IOException;import java.util.LinkedHashMap;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet implementation class CarServlet */public class CarServlet extends HttpServlet {	private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public CarServlet() {        super();        // TODO Auto-generated constructor stub    }	/**	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)	 */	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {				//1.设置编码格式		response.setContentType("text/html;charset = utf-8");		//2.获取到对应的id		int id =Integer.parseInt( request.getParameter("id"));	//0.1.2.3			//取到对应的id的值		String[] names = {"手机一","手机二","手机三","手机四",};			//取到对应的id的商品的名称		String name = names[id];		//3.将购物车的信息存放到session中去  map
   
    		Map
    
      map =  (Map
     
      ) request.getSession().getAttribute("cart");		/*		 第一次调用的时候，map为空 就new一个map 存到session中去  		 但是第二次就不走这个步骤了		 */		if(map ==null) {   //购物车为空的时候 session中没有任何东西哦			map = new LinkedHashMap
      
       ();			request.getSession().setAttribute("cart", map);  //创建session		}		//4.判断session中有没有存放该商		if(map.containsKey(name)) {			//有，在原来的基础上加一			map.put(name, map.get(name)+1);		}else {			//没有购买该商品时			map.put(name, 1);		}		//5.输出界面		response.getWriter().write("
       
继续购物");		response.getWriter().write("
       结算
");			}	/**	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)	 */	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {		// TODO Auto-generated method stub		doGet(request, response);	}}
      
     
    
   

3.显示购物车页面

<%@page import="java.util.Map"%><%@ page language="java" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%>
   
您购买的商品如下
<%//获取map	Map
   
     map =(Map
    
     ) session.getAttribute("cart");//便利mapif(map != null){	for(String key:map.keySet()){		int value = map.get(key);		%>	
     
名称：<%=key %> 数量 ：<%=value %>
<%	}}%>
     
清空购物车
    
   

4.清空购物车处理

package com.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * Servlet implementation class cleanCa */public class cleanCa extends HttpServlet {	private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public cleanCa() {        super();        // TODO Auto-generated constructor stub    }	/**	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)	 */	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {		//1.获取session		HttpSession session = request.getSession();		session.removeAttribute("cart");		//移除name		response.sendRedirect("cart.jsp");		//回到当前的页面	}	/**	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)	 */	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {		// TODO Auto-generated method stub		doGet(request, response);	}}

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