JSP实现购物车功能（session+Map）

记录一下从上个项目中抽离出来的购物车功能：Jsp+Session+Map

先来看一下最后效果吧
我们先来整理一下购物车的开发思路：
1.确定将哪本书放入购物车，使用id来进行传值或者直接从Session取出
2.判断是否存在购物车，若存在则直接使用，不存在则创建
3.判断购物车是否存在当前存入的这本书，若存在，数量加1，否则存入该书，设置初始数量为1
4.将购物车存入Session,方便前台获取

---

下面开始放代码

首先创建实体类：

package com.servlet;

/**
 * Book实体类
 */
public class Book {
    private Integer id;
    private String name;
    private  double price;

    public Book() {
    }

    public Book(int id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

数据库链接MySqlDao类：

package com.untils;

import java.beans.Statement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLClientInfoException;
import java.sql.SQLException;

/**
 * @title BaseDao
 * @author Bailu
 * @time 下午1:08:11
 *
 */
//数据库连接和关闭类
/**
 * 加载驱动
 * 创建连接对象
 * 准备sql语句
 * 创建执行对象
 * 执行并获取结果
 * 释放链接
 */
public class MysqlDB {
    public static Connection conn=null;
    public static PreparedStatement state= null;
    public static ResultSet result=null;


    public static Connection getConn() throws SQLException,ClassNotFoundException {
        Class.forName("com.mysql.cj.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/shopping?useSSL=false&serverTimezone=Asia/Shanghai&allowPublicKeyRetrieval=true","root","root");//此处所用数据库为mysql8.0 其他版本的链接信息需要自行更改一下
        return conn;
    }
    /**
     *数据更新
     */
    public static int update(String sql,Object...obs) {
        int result = 0;
        try{
            conn = getConn();
            state = conn.prepareStatement(sql);
            for (int i = 0; i < obs.length; i++) {
                state.setObject(i+1, obs[i]);
            }
            result = state.executeUpdate();

        }catch(Exception e){
            e.printStackTrace();
        }
        return result;

    }
    /**
     *查询
     */
    public static ResultSet query(String sql,Object...obs) {
        try {
            conn=getConn();
            state=conn.prepareStatement(sql);
            for (int i = 0; i < obs.length; i++) {
                state.setObject(i+1, obs[i]);
            }
            result=state.executeQuery();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

    public static void closeObject(){
        try {
            if(result!=null){
                result.close();
            }
            if(result!=null){
                result.close();
            }
            if(result!=null){
                result.close();
            }
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
    }

}

接下来写数据交互层：
首先定义好接口再实现

package com.dao;

import com.servlet.Book;

import java.util.List;

/**
 * BookDao接口
 */
public interface BookDao {
/**
*
**/ 
    public List<Book> select(String sql, Object[] arr);

    public Book getBook(Integer id);

}

接口实现：

package com.servlet;

import com.dao.BookDao;
import com.servlet.Book;
import com.untils.MysqlDB;

import java.util.ArrayList;
import java.util.List;

/**
 * BookDao接口实现
 */
public class BookDaoImpl implements BookDao {
    @Override
    public List<Book> select(String sql, Object[] arr) {
        MysqlDB.result = MysqlDB.query(sql);
        List<Book> list = new ArrayList<Book>();
        try {
            while (MysqlDB.result.next()){
                Book book = new Book();
                book.setId(MysqlDB.result.getInt("id"));
                book.setName(MysqlDB.result.getString("name"));
                book.setPrice(MysqlDB.result.getDouble("price"));
                list.add(book);
            }
            return  list;
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            MysqlDB.closeObject();
        }
        return null;
    }

    @Override
    public Book getBook(Integer id) {
        String sql = "select * from cart where id = ? ";
        MysqlDB.result = MysqlDB.query(sql,id);
        try {
            while (MysqlDB.result.next()){
                Book books = new Book();
                books.setId(MysqlDB.result.getInt("id"));
                books.setName(MysqlDB.result.getString("name"));
                books.setPrice(MysqlDB.result.getDouble("price"));
                return books;
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            MysqlDB.closeObject();
        }
        return null;
    }
}

实现接口：

package com.dao;

import com.servlet.Book;

import java.util.List;

public interface BookService {
    public List<Book> select(Book book);

    public Book getBook(Book book);
}

具体实现：

package com.servlet;

import com.dao.BookDao;
import com.dao.BookService;

import java.util.ArrayList;
import java.util.List;

public class BookServiceImpl implements BookService {
    private BookDao dao=new BookDaoImpl();
    @Override
    public List<Book> select(Book book) {
        StringBuilder  sql = new StringBuilder("select * from cart where 1=1") ;
        List<Object> list=new ArrayList<Object>();
        if(book!= null){
            if(book.getId() != null &&book.getId()!=0){
                sql.append("and id=?");
                System.out.println(sql);
                list.add(book.getId());
            }
        }
        return dao.select(sql.toString(), list.toArray());
    }

    @Override
    public Book getBook(Book book) {
        if(book.getId() != null &&book.getId()!=0){
            System.out.println("这个是BookServiceImpl的book.getID:"+book.getId());
             return dao.getBook(book.getId());
        }
        return null;
    }
}

接下来写jsp+servlet:

<%@ page import="java.util.Date" %>
<%@ page import="java.util.List" %>
<%@ page import="com.servlet.Book" %>
<%@ page import="com.servlet.BookServiceImpl" %><%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2020-02-25
  Time: 13:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%--图书列表显示页面-这里建议直接用El表达式写-%>
<html>
<head>
    <title>$Title$</title>
</head>
<body>
<div>
    <table>
        <tr><th>id</th><th>name</th><th>price</th><th>cart</th></tr>
        <%

            List<Book> list = (List<Book>) request.getAttribute("list");
            for(Book b:list){
        %>
        <tr align="center">
            <td><%=b.getId() %></td>
            <td><%=b.getName() %></td>
            <td><%=b.getPrice() %></td>
            <td><a href="add?id=<%=b.getId()%>">添加到购物车</a></td>
        </tr>
        <%} %>
    </table>
</div>
</body>
</html>

图书列表显示Servlet:

package com.servlet;

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

@WebServlet(name = "ShowServlet",value = "/showlist")
public class ShowServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Book book = new Book();
        BookServiceImpl service = new BookServiceImpl();
        List<Book> list = service.select(book);
        request.setAttribute("list",list);
        request.getRequestDispatcher("/jsp/shoppinglist.jsp").forward(request,response);
    }
}

接下来我们写购物车，首先创建一个购物车实体类。存购物车信息和数量

package com.servlet;

/**
 * Cartitem实体类
 */
public class CartItem {
    private Book book;
    private Integer number;

    public CartItem() {

    }

    public CartItem(Book book, Integer number) {
        this.book = book;
        this.number = number;
    }

    public Book getBook() {
        return book;
    }

    public void setBook(Book book) {
        this.book = book;
    }

    public Integer getNumber() {
        return number;
    }

    public void setNumber(Integer number) {
        this.number = number;
    }
}

这里就是购物车的核心部分了：

package com.servlet;

import com.dao.BookService;

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

@WebServlet(name = "addSeeionServlet",value = "/add")
public class addSeeionServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Book book=new Book();
        //接收需要添加购物车的商品id
        String sid=request.getParameter("id");
        Integer id=Integer.parseInt(sid);
        BookService service=new BookServiceImpl();
        book.setId(id);
        Book books=service.getBook(book);
        HttpSession session = request.getSession();
        //判断session是否存在购物车
        Map<Integer, CartItem> cart = (Map<Integer, CartItem>) session.getAttribute("cart");
        if(cart == null){
        //若不存在则创建
            cart = new HashMap<>();
        }
        //考虑购物车是否存在该商品，
        CartItem cartItem = cart.get(books.getId());
        if(cartItem == null){
            cartItem = new CartItem();
            //若不存在，将该商品添加进购物车
            cartItem.setBook(books);
            //设初始数量为1
            cartItem.setNumber(1);
        }else{
        //若存在，则数量+1
            cartItem.setNumber(cartItem.getNumber()+1);
        }
        cart.put(books.getId(),cartItem);
        //将购物车存入Session
        session.setAttribute("cart",cart);
        request.getRequestDispatcher("/jsp/add.jsp").forward(request,response);
    }
}

购物车的展示页面：

<%@ page import="com.servlet.CartItem" %>
<%@ page import="java.util.Map" %>
<%@ page import="com.servlet.Book" %><%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2020-03-04
  Time: 17:25
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>添加商品</title>
</head>
<body>
添加完成
<table width="100%" align="center" border="1px">
    <tr>
        <th>id</th>
        <th>name</th>
        <th>price</th>
        <th>count price</th>
        <th>unit cost</th>

    </tr>
    <%
        Map<Integer,CartItem> map=(Map<Integer,CartItem>)session.getAttribute("cart");
        //2:将购物车里面的内容遍历出来
        double count=0;//显示出总价格
        for(Map.Entry<Integer,CartItem> entry : map.entrySet()){
            //计算出每一样的书籍一共花了多少钱
            double price=entry.getValue().getBook().getPrice() * entry.getValue().getNumber();
            //计算出一共花了多少钱
            count=count+price;
    %>
    <tr align="center">
        <td><%=entry.getKey() %></td>
        <td><%=entry.getValue().getBook().getName() %></td>
        <td><%=entry.getValue().getBook().getPrice() %></td>
        <td><%=entry.getValue().getNumber() %></td>
        <td><%=entry.getValue().getBook().getPrice() * entry.getValue().getNumber()%></td>

    </tr>
    <%} %>
    <tr>
        <td colspan="4" align="right">价格总计</td>
        <td><%=count %></td>
    </tr>
</table>
</body>
</html>

这是一个非常简陋的购物车，还需要完善，加油！