HttpSession小應用：購物車案例

案例：購物車應用：
Book:簡單的書籍描述；類

Bookdb代碼：
public class Bookdb {
 private static Map<String,Book> books=new HashMap<String, Book>();
 static{
  books.put("1", new Book("1", "玉女心經", "hehe"));
  books.put("2", new Book("2", "辟邪劍譜", "haha"));
  books.put("3", new Book("3", "葵花寶典", "xixi"));
 }
 //獲取全部書籍的方法
 public static Map<String, Book> findAllBooks(){
  return books;
 }
 public static Book findBookbyid(String bookId){
  return books.get(bookId);
 }
}

顯示全部的書籍頁面：
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("全部的書籍："+"<br/>");
   //獲取books集合，遍歷
   Map<String, Book> me=Bookdb.findAllBooks();
   //獲取集合中的value值，即book對象
   Set<Map.Entry<String, Book>> se=me.entrySet();
   //獲取book對象的name屬性
   //打印name屬性，並建立購買鏈接，鏈接中須要將書籍的id屬性返回給購買成功界面
   for(Map.Entry<String, Book> books:se){
    out.write(books.getValue().getName()+"<a href='"+request.getContextPath()+"/servlet/BuyBook?bookId="+books.getKey()+"'>購買</a>"+"<br/>");
   }
   //查看購物車
   out.write("<a href='"+request.getContextPath()+"/servlet/ShowCart'>查看購物車</a>");
 }

存入頁面代碼：
BuyBook:
public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter out=response.getWriter();
   //將商品放到購物車，購物車應當是一個集合
  String bookId=request.getParameter("bookId");
  //獲取到須要購買的書籍對象
  Book book=Bookdb.findBookbyid(bookId);
  //必需要現有一個購物車
  HttpSession session=request.getSession();
  List<Book> cart=(List<Book>) session.getAttribute("cart");
  if(cart==null){
   cart=new ArrayList<Book>();
   session.setAttribute("cart", cart);
  }
  //到這裏，一定有購物車
  cart.add(book);
  out.write("已經放入購物車"+"<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>繼續購物</a>");
 }

購物車頁面：
ShowCart代碼：
public class ShowCart extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   //購物車
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter out=response.getWriter();
  //獲取到購物車內的全部book對象，遍歷
  HttpSession session=request.getSession();
  List<Book> list=(List<Book>) session.getAttribute("cart");
  if(list==null){
   out.write("請先挑選商品"+"<br/>");
   out.write("<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>返回購物界面</a>"+"<br/>");
  }else{
   out.write("您放入購物車的商品以下："+"<br/>");
   for(Book books:list){
    out.write(books.getName()+"<br/>");
   }
   out.write("<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>返回購物界面</a>"+"<br/>");
   out.write("<a href='"+request.getContextPath()+"/servlet/ClearCart'>清空購物車</a>");
  }
  //清空購物車
 }

 清空購物車頁面：
 ClearCart代碼：
 public class ClearCart extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   //清空購物車
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter out=response.getWriter();
  //獲取session對象，將session刪除
  HttpSession session=request.getSession();
  //清空session
  session.removeAttribute("cart");
  out.write("已經清空您的購物車"+"<br/>");
  out.write("<a href='"+request.getContextPath()+"/servlet/ShowAllBooks'>返回購物界面</a>");
 }