一、新建项目、实体类、servlet

1.新建Dynamic Web project，新建过程如下；

2.在src目录下新建两个包，一个命名为entity，一个命名为servlet，新建过程如下；

3.在entity目录下新建两个实体类，一个名为Cake,一个名为CakeDB,新建过程如下：
4.在servlet目录下新建三个servlet，命名分别为ListCakeServlet、PurchaseServlet和CartServlet，新建过程如下：

所有东西建完后结果如图：

二：源代码

1.Cake实体类：

package entity;

public class Cake {
	private String id;
	private String name;
	
	public Cake() {
	}
	public Cake(String id, String name) {
		this.id = id;
		this.name = name;
	}
	
	public void setId(String id) {
		this.id=id;
	}
	public String getId() {
		return id;
	}
	
	public void setName(String name) {
		this.name=name;
	}
	public String getName() {
		return name;
	}
}

2.CakeDB实体类：

package entity;

import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;

public class CakeDB {
	private static Map<String, Cake> cake = new LinkedHashMap<String, Cake>();
    static {//模拟数据库中的记录
        cake.put("1001", new Cake("1001", "A类：巧克力蛋糕"));
        cake.put("1002", new Cake("1002", "B类：水果沙拉蛋糕"));
        cake.put("1003", new Cake("1003", "C类：慕斯蛋糕"));
        cake.put("1004", new Cake("1004", "D类：奶油蛋糕"));
        cake.put("1005", new Cake("1005", "E类：干果蛋糕"));
    }
    // 获得所有的蛋糕
    public static Collection<Cake> getAll() {
        return cake.values();
    }
    // 根据指定的id获蛋糕
    public static Cake getCake(String id) {
        return cake.get(id);
    }
}

3.ListCakeServlet：

package servlet;

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

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

import entity.Cake;
import entity.CakeDB;

@WebServlet("/ListCakeServlet")
public class ListCakeServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

    public ListCakeServlet() {
        super();
    }

	protected void doGet(HttpServletRequest request, HttpServletResponse resp) 
			throws ServletException, IOException {
		resp.setContentType("text/html;charset=utf-8");
        PrintWriter out = resp.getWriter();
        Collection<Cake> cakes = CakeDB.getAll();
        out.write("本站提供的蛋糕有：<br>");
        for (Cake cake : cakes) {
            String url = "PurchaseServlet?id=" + cake.getId();
            out.write(cake.getName() + "<a href='" + url
                    + "'>点击购买</a><br>");
        }
	}

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

4.PurchaseServlet：

package servlet;

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

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;

import entity.Cake;
import entity.CakeDB;

@WebServlet("/PurchaseServlet")
public class PurchaseServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    public PurchaseServlet() {
        super();
    }

	protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
			throws ServletException, IOException {
		// 获得用户购买的商品
        String id = req.getParameter("id");
        if (id == null) {
            // 如果id为null，重定向到ListBookServlet页面
            String url = "ListBookServlet";
            resp.sendRedirect(url);
            return;
        }
        Cake book = CakeDB.getCake(id);
        // 创建或者获得用户的Session对象
        HttpSession session = req.getSession();
        // 从Session对象中获得用户的购物车
        List<Cake> cart = (List) session.getAttribute("cart");
        if (cart == null) {
            // 首次购买，为用户创建一个购物车(List集合模拟购物车)
            cart = new ArrayList<Cake>();
            // 将购物城存入Session对象
            session.setAttribute("cart", cart);
        }
        // 将商品放入购物车
        cart.add(book);
        // 创建Cookie存放Session的标识号
        Cookie cookie = new Cookie("JSESSIONID", session.getId());
        cookie.setMaxAge(60 * 30);
        cookie.setPath("/Servlet");
        resp.addCookie(cookie);
        // 重定向到购物车页面
        String url = "CartServlet";
        resp.sendRedirect(url);
	}

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

}

5.CartServlet:

package servlet;


import entity.Cake;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

@WebServlet("/CartServlet")

public class CartServlet extends HttpServlet {



    protected void  doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter out = resp.getWriter();
        List<Cake> cart = null;
        boolean purFlag = true;
        HttpSession session = req.getSession(false);
        if (session == null)
        {
            purFlag =false;
        }
        else {
            cart = (List) session.getAttribute("cart");

            if (cart == null){
                purFlag=false;
            }
        }

        if(!purFlag){
            out.write("抱歉，您还没有购买任何商品！<br>");
        }
        else {
            out.write("您购买的蛋糕有：<br>");
            double price = 0;
            for (Cake cake:cart){
                out.write(cake.getName() +"<br>");
            }
        }

    }


}

三、运行

1.在ListCakeServlet文件下运行，点击鼠标右键，选择run as，具体如图:

2.运行结果如图：

点击购买之后跳转CartServlet页面，比如我点了巧克力蛋糕后：

以上就是使用Session和cookie会话对象实现简单购物车功能。希望对你有帮助哦~