用session实现简单的购物

 package cn.itcast.shopping;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.Map;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import cn.itcast.Book;
 import cn.itcast.Db;

 public class ListBookServlet extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setCharacterEncoding("UTF-8");
         response.setContentType("text/html;charset=UTF-8");
         PrintWriter out = response.getWriter();

         out.write("本网站有如下商品：<br/>");
         Map<String,Book> map = Db.getAll();
         for (Map.Entry<String, Book> entry : map.entrySet()) {
             Book book = entry.getValue();
             out.print(book.getName()+"<a href='/ServletDemo/servlet/BuyServlet?id="+book.getId()+"' target='_blank'>购买</a><br/>");
         }

     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

     }

 }

 package cn.itcast.shopping;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.List;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;

 import cn.itcast.Book;
 import cn.itcast.Db;

 //完成购买
 public class BuyServlet extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

          String id = request.getParameter("id");
          Book book = (Book) Db.getAll().get(id);

          HttpSession session =request.getSession();

          //从Session得到用户名用于保存所有书的集合（购物车）
          List list = (List) session.getAttribute("list");
          if(list==null){
              list = new ArrayList();
              session.setAttribute("list", list);
          }
          list.add(book);

         // request.getRequestDispatcher("/servlet/ListCarServlet").forward(request, response);
          response.sendRedirect(request.getContextPath()+"/servlet/ListCarServlet");
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

     }

 }

 package cn.itcast.shopping;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.List;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;

 import cn.itcast.Book;

 //显示用户购买商品
 public class ListCarServlet extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setCharacterEncoding("UTF-8");
         response.setContentType("text/html;charset=UTF-8");
         PrintWriter out = response.getWriter();

         HttpSession session = request.getSession(false);
         if(session==null){
             out.write("您没有购买任何商品！！");
             return;
         }

         out.write("您购买了如下商品：<br/>");
         List<Book> list = (List) session.getAttribute("list");
         for(Book book : list){
             out.write(book.getName());
         }
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

     }

 }

 package cn.itcast;

 import java.util.LinkedHashMap;
 import java.util.Map;

 public class Db {
     private static Map<String, Book> map = new LinkedHashMap();

     static{
         map.put("1", new Book("1","javaweb开发","Zero","一本好书！！"));
         map.put("2", new Book("2","jdbc开发","one","一本好书！！"));
         map.put("3", new Book("3","spring开发","two","一本好书！！"));
         map.put("4", new Book("4","struks开发","three","一本好书！！"));
         map.put("5", new Book("5","hibernate开发","four","一本好书！！"));
     }

     public static Map getAll(){
         return map;
     }
 }

 package cn.itcast;

 import java.io.Serializable;

 public class Book implements Serializable {
     private String id;
     private String name;
     private String author;
     private String description;

     public Book(String id, String name, String author, String description) {
         super();
         this.id = id;
         this.name = name;
         this.author = author;
         this.description = description;
     }

     public String getId() {
         return id;
     }

     public void setId(String id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public String getAuthor() {
         return author;
     }

     public void setAuthor(String author) {
         this.author = author;
     }

     public String getDescription() {
         return description;
     }

     public void setDescription(String description) {
         this.description = description;
     }
 }