【jsp】案例：显示商品列表 & 问题：List内添加元素，为什么值都变成一样的了

代码：

1.Product：

package domain;

public class Product {
    
/*    `pid` varchar(50) NOT NULL,
      `pname` varchar(150) DEFAULT NULL,
      `market_price` double DEFAULT NULL,
      `shop_price` double DEFAULT NULL,
      `pimage` varchar(200) DEFAULT NULL,
      `pdate` date DEFAULT NULL,
      `is_hot` int(11) DEFAULT NULL,
      `pdesc` varchar(255) DEFAULT NULL,
      `pflag` int(11) DEFAULT NULL,
      `cid` varchar(50) DEFAULT NULL,
      PRIMARY KEY (`pid`)*/
    
    private String pid;
    private String pname;
    private double market_price;
    private double shop_price;
    private String pimage;
    private String pdate;
    private int is_hot;
    private String pdesc;
    private int pflag;
    private String cid;
    
    public Product(){
        pid="";
        pname="";
        pimage="";
        pdate="";
        pdesc="";
        cid="";
    }
    
    public String getPid() {
        return pid;
    }
    public void setPid(String pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    public double getMarket_price() {
        return market_price;
    }
    public void setMarket_price(double market_price) {
        this.market_price = market_price;
    }
    public double getShop_price() {
        return shop_price;
    }
    public void setShop_price(double shop_price) {
        this.shop_price = shop_price;
    }
    public String getPimage() {
        return pimage;
    }
    public void setPimage(String pimage) {
        this.pimage = pimage;
    }
    public String getPdate() {
        return pdate;
    }
    public void setPdate(String pdate) {
        this.pdate = pdate;
    }
    public int getIs_hot() {
        return is_hot;
    }
    public void setIs_hot(int is_hot) {
        this.is_hot = is_hot;
    }
    public String getPdesc() {
        return pdesc;
    }
    public void setPdesc(String pdesc) {
        this.pdesc = pdesc;
    }
    public int getPflag() {
        return pflag;
    }
    public void setPflag(int pflag) {
        this.pflag = pflag;
    }
    public String getCid() {
        return cid;
    }
    public void setCid(String cid) {
        this.cid = cid;
    }
    
}

2.ProductListD

package dao;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

import domain.Product;

public class ProductListDao {

    public List<Product> getAllProduct(){
        List<Product> productList=new ArrayList<Product>();//List是接口，不能直接new List
//        Product product=new Product();//不能只定义一个变量，页面上只显示最后一个商品
        
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        try {
            Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/web17","root","root");
            PreparedStatement ps=con.prepareStatement("select * from product");
            ResultSet rs=ps.executeQuery();
//            int i=0;
            while(rs.next()) {
                Product product=new Product();
                
                product.setPid(rs.getString(1));
                product.setPname(rs.getString(2));
                product.setMarket_price(rs.getInt(3));
                product.setShop_price(rs.getInt(4));
                product.setPimage(rs.getString(5));
                product.setPdate(rs.getString(6));
                product.setIs_hot(rs.getInt(7));
                product.setPdate(rs.getString(8));
                product.setPflag(rs.getInt(9));
                product.setCid(rs.getString(10));
                
//                System.out.println(product.getPname());
                productList.add(product);
//                System.out.println(productList.get(i).getPname());
//                i++;
            }
            
            rs.close();
            ps.close();
            con.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        
        return productList;
    }
    
}

3.ProductListServlet

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 dao.ProductListDao;
import domain.Product;

public class ProductListServlet extends HttpServlet {

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

        ProductListDao productListDao=new ProductListDao();
        List<Product> productList=productListDao.getAllProduct();
//        System.out.println(productList.isEmpty());
        
        request.setAttribute("productList", productList);
        request.getRequestDispatcher("/product_list.jsp").forward(request, response);
        
    }

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

}

4.product_list.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import="java.util.*"%>
<%@ page import="domain.*"%>
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>会员登录</title>
<link rel="stylesheet" href="css/bootstrap.min.css" type="text/css" />
<script src="js/jquery-1.11.3.min.js" type="text/javascript"></script>
<script src="js/bootstrap.min.js" type="text/javascript"></script>
<!-- 引入自定义css文件 style.css -->
<link rel="stylesheet" href="css/style.css" type="text/css" />

<style>
body {
    margin-top: 20px;
    margin: 0 auto;
     100%;
}

.carousel-inner .item img {
     100%;
    height: 300px;
}
</style>
</head>

<body>


    <!-- 引入header.jsp -->
    <jsp:include page="/header.jsp"></jsp:include>


    <div class="row" style=" 1210px; margin: 0 auto;">
        <div class="col-md-12">
            <ol class="breadcrumb">
                <li><a href="#">首页</a></li>
            </ol>
        </div>

        <%
            List<Product> productList = (List<Product>) request.getAttribute("productList");

            if (productList != null) {
                for (Product product : productList) {

                    out.write("<div class='col-md-2'>");
                    out.write("<a href='product_info.htm'> <img src='"+product.getPimage()+"' width='170' height='170' style='display: inline-block;'>");
                    out.write("</a>");
                    out.write("<p>");
                    out.write("<a href='product_info.html' style='color: green'>"+product.getPname()+"</a>");
                    out.write("</p>");
                    out.write("<p>");
                    out.write("<font color='#FF0000'>商城价：&yen;"+product.getShop_price()+"</font>");
                    out.write("</p>");
                    out.write("</div>");

                }
            }
        %>

    </div>

    <!--分页 -->
    <div style=" 380px; margin: 0 auto; margin-top: 50px;">
        <ul class="pagination" style="text-align: center; margin-top: 10px;">
            <li class="disabled"><a href="#" aria-label="Previous"><span
                    aria-hidden="true">&laquo;</span></a></li>
            <li class="active"><a href="#">1</a></li>
            <li><a href="#">2</a></li>
            <li><a href="#">3</a></li>
            <li><a href="#">4</a></li>
            <li><a href="#">5</a></li>
            <li><a href="#">6</a></li>
            <li><a href="#">7</a></li>
            <li><a href="#">8</a></li>
            <li><a href="#">9</a></li>
            <li><a href="#" aria-label="Next"> <span aria-hidden="true">&raquo;</span>
            </a></li>
        </ul>
    </div>
    <!-- 分页结束 -->

    <!--商品浏览记录-->
    <div
        style=" 1210px; margin: 0 auto; padding: 0 9px; border: 1px solid #ddd; border-top: 2px solid #999; height: 246px;">

        <h4 style=" 50%; float: left; font: 14px/30px 微软雅黑">浏览记录</h4>
        <div style=" 50%; float: right; text-align: right;">
            <a href="">more</a>
        </div>
        <div style="clear: both;"></div>

        <div style="overflow: hidden;">

            <ul style="list-style: none;">
                <li
                    style=" 150px; height: 216; float: left; margin: 0 8px 0 0; padding: 0 18px 15px; text-align: center;"><img
                    src="products/1/cs10001.jpg" width="130px" height="130px" /></li>
            </ul>

        </div>
    </div>


    <!-- 引入footer.jsp -->
    <jsp:include page="/footer.jsp"></jsp:include>

</body>

</html>

结果：

http://localhost:8080/WEB17_2/ProductListServlet

注意：

加入List内的元素只保存了地址，而不是复制元素。将元素加入List后，修改该元素值，会影响到List内的元素值。所以每次放入一个新元素都需要new一个新地址。否则结果只有最后一个元素值，前面的元素值都被覆盖了。