用session实现简单的购物车

列出所有书籍，用一个类来模拟数据库

//代表网站首页，列出所有书
@WebServlet(name = "ListBookServlet",urlPatterns = "/ListBookServlet")
public class ListBookServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected 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.print("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 = '/BuyServlet?id="+book.getId()+ "'_target = _blank'>购买</a>");
        }
    }
}
    class Db{
        private static Map<String , book> map = new LinkedHashMap();
        static{
            map.put("1",new book("1","javaweb","aa","good"));
            map.put("2",new book("2","jdbc","bb","good"));
            map.put("3",new book("3","jvm","cc","good"));
            map.put("4",new book("4","c#","dd","good"));
            map.put("5",new book("5","spring","ee","good"));
        }
        public static Map getAll(){

            return map;
        }

    }
    class book{
        private String id;
        private String name;
        private String author;
        private String description;

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

        public book() {
        }

        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;
        }

        public String getId() {

            return id;
        }

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

}

购买

//购买
@WebServlet(name = "BuyServlet",urlPatterns = "/BuyServlet")
public class BuyServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    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();

        //从session得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);

        //request.getRequestDispatcher("/ListCarServlet").forward(request,response); 转发，刷新后会重新执行当前操作，不可用
        response.sendRedirect("ListCarServlet");


    }
}

显示用户购买的商品

//显示用户购买的商品
@WebServlet(name = "ListCarServlet",urlPatterns = "/ListCarServlet")
public class ListCarServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected 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();
        if(session == null){
            out.print("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<book>) session.getAttribute("list");
        for(book book : list){
            out.write(book.getName());
        }

    }
}