Java model1

亦凉 2021-05-03 17:22 291阅读 0赞

## 概述： ##

![这里写图片描述][SouthEast]

1.  界面层：由JSP页面进行与客户端浏览器的交互，可以直接调用JavaBean
2.  业务逻辑层：由JavaBean进行处理业务逻辑，封装数据，并与数据库层进行交互
3.  数据库层：底层数据库，可被javaBean访问

优点：避免了JSP页面直接进行业务逻辑处理所带来的维护性，扩展性差的弱点.体现了分层设计的思想

缺点：Model 1模式的实现比较简单，适用于快速开发小规模项目。但从工程化的角度看，它的局限性非常明显：JSP页面身兼View和Controller两种角色，将控制逻辑和表现逻辑混杂在一起，从而导致代码的重用性非常低，增加了应用的扩展性和维护的难度。

## 实例： ##

需求：完成商品的展示与详细信息查看  
分析：使用model1实现，javabean负责与数据库交互，实现业务逻辑，jsp负责与浏览器交互，页面展示

![这里写图片描述][SouthEast 1]

**Items类**\-商品实体类，数据库表的映射

package entity;
    public class Items {
    
        private int id; // 商品编号
        private String name; // 商品名称
        private String city; // 产地
        private int price; // 价格
        private int number; // 库存
        private String picture; // 商品图片
        ..............
        setter，getter方法
    }

**DBHelper类** \-提供数据库连接，提高代码复用性

package util;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;
    
    public class DBHelper { 
        private static final String driver = "com.mysql.jdbc.Driver";
        private static final String url = "jdbc:mysql://localhost:3306/shopping?useUnicode=true&characterEncoding=UTF-8";
        private static final String username = "root";
        private static final String password = "970728";
        private static Connection con = null;
        static{
            try {
                Class.forName(driver);
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        public static Connection getConnection(){
            if (con == null) {
                try {
                    con = DriverManager.getConnection(url,username,password);
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                return con;
            }
            return con;
        }
    }

**ItemsDAO类**\-实现业务逻辑

package dao;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.util.ArrayList;
    import util.DBHelper;
    import entity.Items;
    
    public class ItemsDAO { 
        //获得所有的商品信息
        public ArrayList<Items> getAllItems()
        {
            ArrayList<Items> list = new ArrayList<Items>();
            Connection con = null;
            PreparedStatement stmt = null;
            ResultSet rs = null;
            try {
                con = DBHelper.getConnection();
                String sql = "select * from Items;";
                stmt = con.prepareStatement(sql);
                rs = stmt.executeQuery();
                while(rs.next())
                {
                    Items item = new Items();
                    item.setId(rs.getInt("id"));
                    item.setName(rs.getString("name"));
                    item.setCity(rs.getString("city"));
                    item.setNumber(rs.getInt("number"));
                    item.setPrice(rs.getInt("price"));
                    item.setPicture(rs.getString("picture"));
                    list.add(item);
                }
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }finally{
                //释放数据集
                if(rs!=null)
                {
                    try {
                        rs.close();
                        rs = null;
                    } catch (Exception e2) {
                        e2.printStackTrace();
                    }
                }
                //释放语句对象
                if(stmt!=null)
                {
                    try {
                        stmt.close();
                        stmt = null;
                    } catch (Exception e3) {
                        e3.printStackTrace();
                    }
                }
            }
            return list;
        }
        //根据商品编号，获取商品资料
        public Items getItemsById(int id)
        {
            Connection con = null;
            PreparedStatement stmt = null;
            ResultSet rs = null;
            Items item = new Items();
            try {
                con = DBHelper.getConnection();
                String sql = "select * from Items where id=?";
                stmt = con.prepareStatement(sql);
                stmt.setInt(1, id);
                rs = stmt.executeQuery();
                if(rs.next())
                {
                    item.setId(rs.getInt("id"));
                    item.setName(rs.getString("name"));
                    item.setCity(rs.getString("city"));
                    item.setNumber(rs.getInt("number"));
                    item.setPrice(rs.getInt("price"));
                    item.setPicture(rs.getString("picture"));
                }
                else 
                    return null;
            } catch (Exception e) {
                e.printStackTrace();
            }finally{
                if(rs!=null)
                {
                    try {
                        rs.close();
                        rs = null;
                    } catch (Exception e2) {
                        e2.printStackTrace();
                    }
                }
                if(stmt!=null)
                {
                    try {
                        stmt.close();
                        stmt = null;
                    } catch (Exception e3) {
                        e3.printStackTrace();
                    }
                }
            }
            return item;
        }
    }

**index.jsp**\-商品展示页

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%>
    <%@ page import="entity.Items"%>
    <%@ page import="dao.ItemsDAO"%>
    
    <style type="text/css"> div { float: left; margin: 10px; } div dd { margin: 0px; font-size: 10pt; } div dd.dd_name { color: blue; } div dd.dd_city { color: #000; } </style>
    </head>
    
    <body>
        <h1>商品展示</h1>
        <hr>
        <center>
            <table width="750" height="60" cellpadding="0" cellspacing="0" border="0">
                <tr>
                    <td>
                         
                        <% ArrayList<Items> list = new ItemsDAO().getAllItems(); if(list!=null&&list.size()>0) { for(int i=0;i<list.size();i++) { Items item = list.get(i); %>
                        <div>
                            <dl>
                                <dt>
                                    <a href="details.jsp?id=<%=item.getId()%>"><img src="images/<%=item.getPicture()%>" width="120" height="90" border="1" /> </a>
                                </dt>
                                <dd class="dd_name"><%=item.getName() %></dd>
                                <dd class="dd_city">
                                    产地:<%=item.getCity() %>  价格:￥<%=item.getPrice() %>
                                </dd>
                            </dl>
                        </div> 
                         
                        <% } } %>
                    </td>
                </tr>
            </table>
        </center>
    </body>
    </html>

**details.jsp**\-商品详细内容页

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8" %>
    <%@ page import="entity.Items"%>
    <%@ page import="dao.ItemsDAO"%>
        <style type="text/css"> div{ float:left; margin-left: 30px; margin-right:30px; margin-top: 5px; margin-bottom: 5px; } div dd{ margin:0px; font-size:10pt; } div dd.dd_name { color:blue; } div dd.dd_city { color:#000; } </style>
      </head>
    
      <body>
        <h1>商品详情</h1>
        <hr>
        <center>
          <table width="750" height="60" cellpadding="0" cellspacing="0" border="0">
            <tr>
              
              <% ItemsDAO itemDao = new ItemsDAO(); Items item = itemDao.getItemsById(Integer.parseInt(request.getParameter("id"))); if(item!=null) { %>
              <td width="70%" valign="top">
                 <table>
                   <tr>
                     <td rowspan="4"><img src="images/<%=item.getPicture()%>" width="200" height="160"/></td>
                   </tr>
                   <tr>
                     <td><B><%=item.getName() %></B></td> 
                   </tr>
                   <tr>
                     <td>产地：<%=item.getCity()%></td>
                   </tr>
                   <tr>
                     <td>价格：<%=item.getPrice() %>￥</td>
                   </tr> 
                 </table>
              </td>
              <% } %></tr>
          </table>
        </center>
      </body>
    </html>

[SouthEast]: /images/20210502/6f20cfe12431403e936e1bb408c81889.png
[SouthEast 1]: /images/20210502/78a384d63106439386d51b96cc90cf93.png