HttpSession session = request.getSession();
 String data = "message form SessionDemo";
 session.setAttribute("data", data);

 response.setContentType("text/html;charset=utf-8");
 PrintWriter writer = response.getWriter();
     
 HttpSession session = request.getSession();
 String data = (String) session.getAttribute("data");
 writer.write(data);

 public class Product {
   private String id;
   private String name;
   private String author;
   
   public Product() {
     super();
   }
 
   public Product(String id, String name, String author) {
     super();
     this.id = id;
     this.name = name;
     this.author = author;
   }
 
   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 class ProductDatabase {
   
   private static Map<String,Product> map = new HashMap<String,Product>();
   
   static{
     map.put("1", new Product("1","《Java编程思想》","JB"));
     map.put("2", new Product("2","《Java核心技术》","fdaf"));
     map.put("3", new Product("3","《Java并发编程》","什么鬼"));
     map.put("4", new Product("4","《Head first 设计模式》","老王"));
     map.put("5", new Product("5","《HTML5权威手册》","hhaa"));
   }
   
   public static Map<String,Product> getMap() {
     
     return map;
   }
 }

 　　response.setCharacterEncoding("UTF-8");
   response.setContentType("text/html;charset=utf-8");
   PrintWriter writer = response.getWriter();
     
   //获取数据库中的商品数据
   Map<String, Product> map = ProductDatabase.getMap();
   for(Map.Entry<String, Product> entry : map.entrySet()) {
     Product book = entry.getValue();
     writer.print(book.getName()+" <a href='/myservlet/servlet/BuySession?id="+book.getId()+"' >购买</a> <br/>");
     }

     //获取用户所购买商品的id号
     String productId = request.getParameter("id");
     Product book =   ProductDatabase.getMap().get(productId);
     
     //将用户所购买的商品加入到Session对象中保存，以便最后一起结账，类似于购物车功能
     HttpSession session = request.getSession();
     List<Product> list = (List<Product>) session.getAttribute("productList");
     if(list == null){
       //首次购买
       list = new ArrayList<Product>();
       session.setAttribute("productList", list);
     }
     
     list.add(book);
     
     //跳转到购物车列表上
     response.sendRedirect("/myservlet/servlet/CartListServlet");

     response.setCharacterEncoding("UTF-8");
     response.setContentType("text/html;charset=utf-8");
     PrintWriter writer = response.getWriter();
     
     writer.print("您购买的商品如下：  <br/>");
     
     HttpSession session = request.getSession();
     List<Product> list = (List<Product>) session.getAttribute("productList");
     for(Product p : list) {
       writer.write(p.getName()+"<br/>");
     }