session 购物车

package session;

import java.io.IOException;
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;

public class SessionDemo4 extends HttpServlet {

protected 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();
//当前网站名，不能够手动指定而是，通过下面的方法获得
//        request.getContextPath();

//从Session的到用户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);

//重定向到购物车显示页面
response.sendRedirect(request.getContextPath()+"/ListCarServlet");
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}