Session对象的应用：实现简单的购物车的功能

ShowAllBooksServlet.java文件：

package com.itheima.session.app1;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//显示所有可购买的商品，提供购买链接
//提供一个查看购物车的链接
public class ShowAllBooksServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        request.getSession();

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        //显示所有可购买的商品，提供购买链接
        out.write("
本站有以下好书：
");

        Map books = BookDB.findAllBooks();
        for(Map.Entry me:books.entrySet()){
            String url = request.getContextPath()+"/servlet/BuyServlet?id="+me.getKey();
            url = response.encodeURL(url);
            out.write(me.getValue().getName()+"  购买
");
        }
        //提供一个查看购物车的链接
        String url = request.getContextPath()+"/servlet/ShowCartServlet";
        url = response.encodeURL(url);
        out.write("查看购物车");
    }

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

}

ShowCartServlet.java文件：

package com.itheima.session.app1;

import java.io.IOException;
import java.io.PrintWriter;
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;
//显示购物车
public class ShowCartServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();

        HttpSession session = request.getSession();
        List cart = (List)session.getAttribute("cart");
        if(cart==null||cart.size()==0){
            out.write("您还没有购买任何商品");
            return;
        }

        out.write("
你购买的商品如下
");
        for(Book b:cart){
            out.write(b.getName()+"
");
        }
    }

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

}

BuyServlet.java文件：

package com.itheima.session.app1;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
//把书籍放入购物车
public class BuyServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String id = request.getParameter("id");
        Book b = BookDB.findById(id);

        //放到HttpSession中》用List来存
        HttpSession session = request.getSession();
        List cart = (List) session.getAttribute("cart");
        if(cart==null){
            cart = new ArrayList();
            session.setAttribute("cart", cart);
        }
        //肯定有购物车
        cart.add(b);
        String url = request.getContextPath()+"/servlet/ShowAllBooksServlet";
        url = response.encodeURL(url);
        out.write(b.getName()+"已放入您的购物车继续购物");

    }

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

}

Book.java文件：

package com.itheima.session.app1;

import java.io.Serializable;

public class Book implements Serializable{
    private String id;
    private String name;
    private String price;
    private String author;
    private String description;
    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 getPrice() {
        return price;
    }
    public void setPrice(String price) {
        this.price = price;
    }
    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;
    }
    @Override
    public String toString() {
        return "Book [id=" + id + ", name=" + name + ", price=" + price
                + ", author=" + author + ", description=" + description + "]";
    }
    public Book(String id, String name, String price, String author,
            String description) {
        super();
        this.id = id;
        this.name = name;
        this.price = price;
        this.author = author;
        this.description = description;
    }
    public Book(){}
}

BookDB.java文件：

package com.itheima.session.app1;

import java.util.HashMap;
import java.util.Map;

//模拟数据
public class BookDB {
    //key:书的id  value：id对应的书
    private static Map books = new HashMap();
    static{
        books.put("1", new Book("1", "葵花宝典", "10", "牛骞", "欲练此功，必须很牛"));
        books.put("2", new Book("2", "欲女心经", "2", "薛振宇", "欲练此功，必须清纯"));
        books.put("3", new Book("3", "金瓶梅", "20", "刘春龙", "爱情经典"));
        books.put("4", new Book("4", "辟邪剑法", "10", "王雷", "欲练此功，必须很牛"));
        books.put("5", new Book("5", "JavaWeb开发", "100", "王昭珽", "经典著作"));
    }
    public static Map findAllBooks(){
        return books;
    }
    public static Book findById(String bookId){
        return books.get(bookId);
    }
}

运行：http://localhost:8080/Session/servlet/ShowAllBooksServlet
结果：你购买的商品如下

欲女心经
葵花宝典
JavaWeb开发