购物车系列教材 （四）- 模块

从开发者的角度来看，购买行为 就是创建一条一条的订单项 
而显示购物车，也就是把这些订单项显示在页面上。 

在这个阶段，订单项都会保存在session中，直到最后生成订单的时候，才会把这些订单项保存在数据库中。

步骤1:SQL
步骤2:OrderItem
步骤3:ProductDAO
步骤4:购买商品
步骤5:显示购物车内容
步骤6:购买相同商品
步骤7:配置web.xml
步骤8:测试
步骤9:练习-删除订单项
步骤10:答案-删除订单项
步骤11:练习-加入购物车
步骤12:答案-加入购物车

步骤 1 : SQL

暂时不需要为OrderItem创建表，因为在这个环节OrderItem还是保存在Session中的

步骤 2 : OrderItem

OrderItem使用属性Product类型的product，而非int类型的pid，因为在后续显示购物车的时候，可以很简单的通过el表达式就显示商品名称和价格了

${oi.product.name}

package bean;

public class OrderItem {

    private int id;

    private Product product;

    private int num;

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public Product getProduct() {

        return product;

    }

    public void setProduct(Product product) {

        this.product = product;

    }

    public int getNum() {

        return num;

    }

    public void setNum(int num) {

        this.num = num;

    }

}

步骤 3 : ProductDAO

因为购买的时候，提交到服务器的是pid, 而OrderItem类的product属性是一个Product类型

所以ProductDAO需要根据id获取Product对象

package dao;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.util.ArrayList;

import java.util.List;

import bean.Product;

public class ProductDAO {

    public static void main(String[] args) {

        System.out.println(new ProductDAO().getProduct(1).getName());

    }

    public Product getProduct(int id) {

        Product result = null;

        try {

            Class.forName("com.mysql.jdbc.Driver");

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/cart?characterEncoding=UTF-8",

                    "root", "admin");

            String sql = "select * from product where id = ?";

            PreparedStatement ps = c.prepareStatement(sql);

            ps.setInt(1, id);

            ResultSet rs = ps.executeQuery();

            if (rs.next()) {

                result = new Product();

                result.setId(id);

                String name = rs.getString(2);

                float price = rs.getFloat(3);

                result.setName(name);

                result.setPrice(price);

            }

            ps.close();

            c.close();

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        return result;

    }

    public List<Product> ListProduct() {

        List<Product> products = new ArrayList<Product>();

        try {

            Class.forName("com.mysql.jdbc.Driver");

            Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/cart?characterEncoding=UTF-8",

                    "root", "admin");

            String sql = "select * from product order by id desc";

            PreparedStatement ps = c.prepareStatement(sql);

            ResultSet rs = ps.executeQuery();

            while (rs.next()) {

                Product product = new Product();

                int id = rs.getInt(1);

                String name = rs.getString(2);

                float price = rs.getFloat(3);

                product.setId(id);

                product.setName(name);

                product.setPrice(price);

                products.add(product);

            }

            ps.close();

            c.close();

        } catch (ClassNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        return products;

    }

}

步骤 4 : 购买商品

购买行为本身就是创建一个OrderItem对象
在负责购买商品的OrderItemAddServlet 中，进行如下流程
1. 获取购买数量
2. 获取购买商品的id
3. 根据id获取商品对象
4. 创建一个新的OrderItem对象
5. 从session中取出一个List , 这个List里面存放陆续购买的商品。
 如果是第一次从session中获取该List,那么它会是空的，需要创建一个ArrayList
6. 把新创建的OrderItem对象放入该List 中
7. 跳转到显示购物车的listOrderItem

package servlet;

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 bean.OrderItem;

import bean.Product;

import dao.ProductDAO;

public class OrderItemAddServlet extends HttpServlet {

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        int num = Integer.parseInt(request.getParameter("num"));

        int pid = Integer.parseInt(request.getParameter("pid"));

        Product p = new ProductDAO().getProduct(pid);

        OrderItem oi = new OrderItem();

        oi.setNum(num);

        oi.setProduct(p);

        List<OrderItem> ois = (List<OrderItem>) request.getSession().getAttribute("ois");

        if (null == ois) {

            ois = new ArrayList<OrderItem>();

            request.getSession().setAttribute("ois", ois);

        }

         

        ois.add(oi);

        response.sendRedirect("/listOrderItem");

    }

}

步骤 5 : 显示购物车内容

显示购物车的OrderItemListServlet 其实什么也没做，因为数据已经在session准备好了，直接服务端跳转到listOrderItem.jsp

在listOrderItem.jsp中，从session中遍历出所有的OrderItem。 因为保存在OrderItem 上的是一个Product对象，所以很容易就可以通过EL表达式遍历出商品的名称和价格。

${oi.product.name}

${oi.product.price}

• OrderItemListServlet.java
• listOrderItem.jsp

package servlet;

import java.io.IOException;

import java.util.List;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import bean.Product;

import dao.ProductDAO;

public class OrderItemListServlet extends HttpServlet

{

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        request.getRequestDispatcher("listOrderItem.jsp").forward(request, response);

    }

}

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8" import="java.util.*" isELIgnored="false"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<h1 align="center" >购物车</h1>

<table align='center' border='1' cellspacing='0'>

    <tr>

        <td>商品名称</td>

        <td>单价</td>

        <td>数量</td>

        <td>小计</td>

    </tr>

    <c:forEach items="${ois}" var="oi" varStatus="st">

        <tr>

            <td>${oi.product.name}</td>

            <td>${oi.product.price}</td>

            <td>${oi.num}</td>

            <td>${oi.product.price*oi.num}</td>

        </tr>

    </c:forEach>

</table>

步骤 6 : 购买相同商品

遍历session中所有的OrderItem

如果找到对应的product.id一样的条目，就调整其数量
如果没有找到，就新增加一条

package servlet;

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 bean.OrderItem;

import bean.Product;

import dao.ProductDAO;

public class OrderItemAddServlet extends HttpServlet {

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        int num = Integer.parseInt(request.getParameter("num"));

        int pid = Integer.parseInt(request.getParameter("pid"));

        Product p = new ProductDAO().getProduct(pid);

        OrderItem oi = new OrderItem();

        oi.setNum(num);

        oi.setProduct(p);

        List<OrderItem> ois = (List<OrderItem>) request.getSession().getAttribute("ois");

        if (null == ois) {

            ois = new ArrayList<OrderItem>();

            request.getSession().setAttribute("ois", ois);

        }

        boolean found = false;

        for (OrderItem orderItem : ois) {

            if (orderItem.getProduct().getId() == oi.getProduct().getId()) {

                orderItem.setNum(orderItem.getNum() + oi.getNum());

                found = true;

                break;

            }

        }

        if (!found)

            ois.add(oi);

        response.sendRedirect("/listOrderItem");

    }

}

步骤 7 : 配置web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app>

    <servlet>

        <servlet-name>ProductListServlet</servlet-name>

        <servlet-class>servlet.ProductListServlet</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>ProductListServlet</servlet-name>

        <url-pattern>/listProduct</url-pattern>

    </servlet-mapping>

    <servlet>

        <servlet-name>UserLoginServlet</servlet-name>

        <servlet-class>servlet.UserLoginServlet</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>UserLoginServlet</servlet-name>

        <url-pattern>/login</url-pattern>

    </servlet-mapping>

    <servlet>

        <servlet-name>OrderItemAddServlet</servlet-name>

        <servlet-class>servlet.OrderItemAddServlet</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>OrderItemAddServlet</servlet-name>

        <url-pattern>/addOrderItem</url-pattern>

    </servlet-mapping>

     

    <servlet>

        <servlet-name>OrderItemListServlet</servlet-name>

        <servlet-class>servlet.OrderItemListServlet</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>OrderItemListServlet</servlet-name>

        <url-pattern>/listOrderItem</url-pattern>

    </servlet-mapping>

</web-app>

步骤 8 : 测试

从登陆页面开始，登陆后到产品显示页面，然后修改购买数量，最后点击购买

http://127.0.0.1/login.jsp

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