(1)用servlet实现简单的购物车系统，项目结构例如以下：（新建web Project项目  仅仅须要AddItemServlet ， ListItemServlet。exam403.jsp三个文件就可以。其它的不用管）

（2）exam403.jsp代码例如以下：

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
     
     
  
        商品:  
          洗衣粉    香皂    食用油    
      
数量:                            查看购物车
     

（3）AddItemServlet代码例如以下：

package com.lc.shoppingCar;import javax.servlet.*;import javax.servlet.http.*;import java.io.*;import java.util.*;public class AddItemServlet extends HttpServlet {    protected void doGet(HttpServletRequest request,HttpServletResponse response)                         throws ServletException,java.io.IOException   {      ServletContext application=getServletContext() ;      ServletConfig config=getServletConfig() ;      response.setContentType("text/html;charset=gb2312");      PrintWriter out=response.getWriter();       HttpSession session =request.getSession();      request.setCharacterEncoding("gb2312");            //读取表单传入的商品ID及数量     String id=request.getParameter("itemID"); 	 String num=request.getParameter("quantity");	 if(id!=null && num.length()!=0)	 {  //从Sessionn中读取购物车		HashMap shoppingCar=(HashMap)session.getAttribute("shoppingCar");	    if(shoppingCar==null)        shoppingCar=new HashMap();	    //将商品加入到购物车中	    String onum=(String)shoppingCar.get(id);	    if(onum==null)	        shoppingCar.put(id,num);	    else	    {	       int n1=Integer.parseInt(num);		   int n2=Integer.parseInt(onum);		   String result=String.valueOf(n1+n2);		   shoppingCar.put(id,result);	     }            //将购物车写回session中保存	     session.setAttribute("shoppingCar",shoppingCar); 	   }	   else  //假设传入的商品ID号为空或数量为空。显示提示信息	     System.out.print("商品ID号为空会或数量为空！");	  //返回商品列表页	  response.sendRedirect("/servletProject/exam403.jsp");         }	      protected void doPost(HttpServletRequest request,HttpServletResponse response)                                throws ServletException,java.io.IOException  {  	   doGet(request,response);  	}}

（4）ListItemServlet代码例如以下：

package com.lc.shoppingCar;import javax.servlet.*;import javax.servlet.http.*;import java.io.*;import java.util.*;public class ListItemServlet extends HttpServlet {    protected void doGet(HttpServletRequest request,HttpServletResponse response)                         throws ServletException,java.io.IOException   {      ServletContext application=getServletContext() ;      ServletConfig config=getServletConfig() ;      response.setContentType("text/html;charset=gb2312");      PrintWriter out=response.getWriter();       HttpSession session =request.getSession();      request.setCharacterEncoding("gb2312");             //从session中获取购物车		HashMap shoppingCar=(HashMap)session.getAttribute("shoppingCar");	  //显示购物车中的内容	   if(shoppingCar!=null)	   {	      Set show=shoppingCar.entrySet();	      Iterator it=show.iterator();	      while(it.hasNext())	      {	        out.print(it.next()+"
");	       }	   }	   else	   	  out.print("购物车为空。");       }	      protected void doPost(HttpServletRequest request,HttpServletResponse response)                                throws ServletException,java.io.IOException  {  	   doGet(request,response);  	}}

（5）实现效果例如以下：

訪问：http://localhost:8080/servletProject/exam403.jsp    学则商品 提交 

点击查看购物车：

OK！

简单的购物车 到此结束！