HttpSession小应用：购物车案例

案例：购物车应用：
Book:简单的书籍描述；类

Bookdb代码：
public class Bookdb {
 private static Map<String,Book> books=new HashMap<String, Book>();
 static{
  books.put("1", new Book("1", "玉女心经", "hehe"));
  books.put("2", new Book("2", "辟邪剑谱", "haha"));
  books.put("3", new Book("3", "葵花宝典", "xixi"));
 }
 //获取所有书籍的方法
 public static Map<String, Book> findAllBooks(){
  return books;
 }
 public static Book findBookbyid(String bookId){
  return books.get(bookId);
 }
}

显示所有的书籍页面：
ShowAllBooks:
public class ShowAllBooks extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   response.setContentType("text/html;charset=UTF-8");
   PrintWriter out=response.getWriter();
   out.write("所有的书籍："+"<br/>");
   //获取books集合，遍历
   Map<String, Book> me=Bookdb.findAllBooks();
   //获取集合中的value值，即book对象
   Set<Map.Entry<String, Book>> se=me.entrySet();
   //获取book对象的name属性
   //打印name属性，并创建购买连接，连接中需要将书籍的id属性返回给购买成功界面
   for(Map.Entry<String, Book> books:se){
    out.write(books.getValue().getName()+"<a href='"+request.getContextPath()+"/servlet/BuyBook?bookId="+books.getKey()+"'>购买</a>"+"<br/>");
   }
   //查看购物车
   out.write("<a href='"+request.getContextPath()+"/servlet/ShowCart'>查看购物车</a>");
 }

存入页面代码：
BuyBook:
public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter out=response.getWriter();
   //将商品放到购物车，购物车应当是一个集合
  String bookId=request.getParameter("bookId");
  //获取到需要购买的书籍对象
  Book book=Bookdb.findBookbyid(bookId);
  //必须要现有一个购物车
  HttpSession session=request.getSession();
  List<Book> cart=(List<Book>) session.getAttribute("cart");
  if(cart==null){
   cart=new ArrayList<Book>();
   session.setAttribute("cart", cart);
  }
  //到这里，必定有购物车
  cart.add(book);
  out.write("已经放入购物车"+"<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>继续购物</a>");
 }

购物车页面：
ShowCart代码：
public class ShowCart extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   //购物车
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter out=response.getWriter();
  //获取到购物车内的所有book对象，遍历
  HttpSession session=request.getSession();
  List<Book> list=(List<Book>) session.getAttribute("cart");
  if(list==null){
   out.write("请先挑选商品"+"<br/>");
   out.write("<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>返回购物界面</a>"+"<br/>");
  }else{
   out.write("您放入购物车的商品如下："+"<br/>");
   for(Book books:list){
    out.write(books.getName()+"<br/>");
   }
   out.write("<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>返回购物界面</a>"+"<br/>");
   out.write("<a href='"+request.getContextPath()+"/servlet/ClearCart'>清空购物车</a>");
  }
  //清空购物车
 }

 清空购物车页面：
 ClearCart代码：
 public class ClearCart extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   //清空购物车
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter out=response.getWriter();
  //获取session对象，将session删除
  HttpSession session=request.getSession();
  //清空session
  session.removeAttribute("cart");
  out.write("已经清空您的购物车"+"<br/>");
  out.write("<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>返回购物界面</a>");
 }