Java代码实现 增删查 + 分页——实习第四天

Posted 2020-09-24 Seraphjin

今天项目内容已经开始了，并且已经完成好多基本操作，今天就开始总结今天学习到的内容，和我遇到的问题，以及分析这其中的原因。

内容模块：

1：Java代码实现对数据库的增删查；

2：分页且获取页面信息；

---

 

这里针对于项目里面的Genre实体，以及对于它的操作进行举例

 1 package com.music.entity;
 2 
 3 public class Genre {
 4     private int id;
 5     private String name;
 6     private String description;
 7     
 8     public int getId() {
 9         return id;
10     }
11     public void setId(int id) {
12         this.id = id;
13     }
14     public String getName() {
15         return name;
16     }
17     public void setName(String name) {
18         this.name = name;
19     }
20     public String getDescription() {
21         return description;
22     }
23     public void setDescription(String description) {
24         this.description = description;
25     }
26     
27 }

Genre.java

 

逻辑层代码展示：

GenreDao:  

 1 package com.music.Dao;
 2 
 3 import java.util.List;
 4 
 5 import com.music.entity.Genre;
 6 
 7 public interface GenreDao {
 8     //查询
 9     public List<Genre> getAll();
10     //删除
11     public boolean deleteGenre(int id);
12     //插入
13     public boolean addGenre(Genre g);
14     //更新
15     public boolean updateGenre(Genre g);
16 }

在这个接口里方法的具体实现GenreDaoImpl:

  1 package com.music.Dao.Impl;
  2 
  3 import java.sql.ResultSet;
  4 import java.sql.SQLException;
  5 import java.util.ArrayList;
  6 import java.util.List;
  7 
  8 import com.music.Dao.GenreDao;
  9 import com.music.entity.Genre;
 10 
 11 public class GenreDaoImpl extends BaseDao implements GenreDao{
 12     
 13     //保存获取结果
 14     ArrayList<Genre> genres = new ArrayList<Genre>();
 15     @Override
 16     public List<Genre> getAll() {
 17         try {
 18             //创建连接
 19             openConnection();
 20             String sql = "select * from genre";
 21             //执行查询，获取结果
 22             ResultSet resultSet = executeQuery(sql, null);
 23             //将查询结果转换成对象
 24             while (resultSet.next()) {
 25                 Genre g = new Genre();
 26                 g.setId(resultSet.getInt("id"));
 27                 g.setName(resultSet.getString("name"));
 28                 g.setDescription(resultSet.getString("description"));
 29                 genres.add(g);
 30             }            
 31         } catch (ClassNotFoundException e) {
 32             
 33             e.printStackTrace();
 34         } catch (SQLException e) {
 35             
 36             e.printStackTrace();
 37         }finally{
 38             closeResourse();
 39         }
 40         return genres;        
 41     }
 42     
 43     @Override
 44     public boolean deleteGenre(int id) {
 45         boolean result = false;
 46         try {
 47             openConnection();
 48             String sql ="delete from genre where id = ?";
 49             result = excute(sql, new Object[]{id});
 50         } catch (ClassNotFoundException e) {
 51             
 52             e.printStackTrace();
 53         } catch (SQLException e) {
 54             
 55             e.printStackTrace();
 56         }finally{
 57             closeResourse();
 58         }        
 59         return result;
 60     }
 61 
 62     @Override
 63     public boolean addGenre(Genre g) {
 64         boolean result = false;
 65         try {
 66             openConnection();
 67             String sql ="insert into genre value(?,?,?)";
 68             result =excute(sql, new Object[]{
 69                     g.getId(),
 70                     g.getDescription(),
 71                     g.getName()
 72             });            
 73         } catch (ClassNotFoundException e) {
 74             e.printStackTrace();
 75         } catch (SQLException e) {
 76             e.printStackTrace();
 77         }finally{
 78             closeResourse();
 79         }    
 80         return result;
 81     }
 82 
 83     @Override
 84     public boolean updateGenre(Genre g) {
 85         boolean result = false;
 86         try {
 87             openConnection();
 88             String sql = "update genre set name = ?, description =? where id=?";
 89             result = excute(sql, new Object[]{
 90                     g.getId()
 91             });
 92         } catch (ClassNotFoundException e) {
 93             
 94             e.printStackTrace();
 95         } catch (SQLException e) {
 96             
 97             e.printStackTrace();
 98         }finally{
 99             closeResourse();
100         }        
101         return result;
102         
103     }
104 
105     public static void main(String[] args) {
106         GenreDaoImpl genreDaoImpl = new GenreDaoImpl();
107         genreDaoImpl.getAll();
108         System.out.println(genreDaoImpl);
109     
110     }
111 
113 }

这里还必须要提出BaseDao:

 1 package com.music.Dao.Impl;
 2 
 3 import java.sql.Connection;
 4 import java.sql.DriverManager;
 5 import java.sql.PreparedStatement;
 6 import java.sql.ResultSet;
 7 import java.sql.SQLException;
 8 
 9 public class BaseDao {
10     //连接数据库    
11     private String className = "com.mysql.jdbc.Driver";
12     private String dburl = "jdbc:mysql://localhost/ZJJ";
13     private String user = "root";
14     private String password = "root";
15     private Connection connection;
16     private PreparedStatement statement;
17     private ResultSet resultSet;
18     
19     public void openConnection() throws ClassNotFoundException, SQLException{
20         //加载驱动
21         Class.forName(className);
22         //创建连接
23         connection = DriverManager.getConnection(dburl,user,password);        
24     }
25     
26     //查询方法
27     public ResultSet executeQuery(String sql,Object[] params) throws SQLException{        
28         statement =connection.prepareStatement(sql);
29         //追加参数
30         if(params !=null){
31             int i=1;
32             for (Object object : params) {
33                 statement.setObject(i, object);    
34                 i++;
35             }
36         }        
37         resultSet =statement.executeQuery();
38         return resultSet;                
39     }
40     
41     //更新
42     public boolean excute(String sql,Object[] params) throws SQLException {
43         statement =connection.prepareStatement(sql);
44         if(params !=null){
45             int i=1;
46             for (Object object : params) {
47                 statement.setObject(i, object);                
48             }
49         }
50         return statement.execute();        
51     }
52     //释放资源
53     public void closeResourse(){
54         try {
55             if(resultSet != null){
56                 resultSet.close();
57             }
58             if(statement != null){
59                 statement.close();
60             }
61             if(connection != null){
62                 connection.close();
63             }
64                         
65         } catch (SQLException e) {
66             // TODO Auto-generated catch block
67             e.printStackTrace();
68         }
69     }
70     
71     
72 
73 }

这个里面的方法都会获得调用。

今天报了一个错误：

错误的原因是：

这个setObject(i,object)有一个好处就是将所有的对象类型都写成object，这样就可以不用分开写各个类型的方法，比较简便。

---

分页：

接口部分：

1 //分页
2     public List<Album> getAlbumWithPage(int genreid,int pageNum,int pageSize);

 

 1 1 public List<Album> getAlbumWithPage(int genreid, int pageNum, int pageSize) 

 

实现部分：

 1 public List<Album> getAlbumWithPage(int genreid, int pageNum, int pageSize) {
 2         ArrayList<Album> albums = new ArrayList<Album>();
 3         //pageNum当前页数
 4         try {
 5             openConnection();
 6             String sql= "select * from album where genreid =? limit ?,?";
 7             ResultSet resultSet = executeQuery(sql, new Object[]{
 8                     genreid,
 9                     (pageNum-1)*pageSize,
10                     pageSize
11             });
12             while (resultSet.next()) {
13                 Album al= new Album();
14                 al.setId(resultSet.getInt("id"));
15                 al.setGenreid(resultSet.getInt("genreid"));
16                 al.setArtist(resultSet.getString("artist"));
17                 al.setTitle(resultSet.getString("title"));
18                 al.setPrice(resultSet.getBigDecimal("price"));
19                 al.setStock(resultSet.getInt("stock"));
20                 al.setDateReleased(resultSet.getString("dateReleased"));
21                 al.setDescription(resultSet.getString("description"));    
22                 albums.add(al);
23             }            
24         } catch (ClassNotFoundException e) {
25             
26             e.printStackTrace();
27         } catch (SQLException e) {
28             
29             e.printStackTrace();
30         }
31         return albums;


       

1 public List<Album> getAlbumWithPage(int genreid, int pageNum, int pageSize) {

    return daoImpl.getAlbumWithPage(genreid, pageNum, pageSize);
 4     }
 5 
 6     @Override
 7     public int getRowCountWithGenreid(int id) {
 8         
 9         return daoImpl.getAlbumWithGenreid(id).size();
10     }

 

JSP代码部分

 1 <%@page import="com.music.entity.Album"%>
 2 <%@page import="com.music.biz.Impl.AlbumBizImpl"%>
 3 <%@page import="com.music.biz.AlbumBiz"%>
 4 <%@page import="com.music.Dao.Impl.AlbumDaoImpl"%>
 5 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 6 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 7 <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
 8   
 9 <html>
10   <head>
11     <title>欢迎光临 Music Store</title>
12     <link type="text/css" rel="Stylesheet" href="style/front.css"/>
13     <script type="text/javascript" src="script/jquery-1.4.1.js"></script>
14   </head>
15   <%
16     AlbumBiz albumItem = new AlbumBizImpl();
17     String id = request.getParameter("genreId");
18     
19     int pageSize =3;
20     int pageNum =1;
21     
22     if(request.getParameter("page")!=null){
23           pageNum =Integer.valueOf(request.getParameter("page"));         
24       }
25       
26     List<Album> albums = albumItem.getAlbumWithPage(Integer.valueOf(id), pageNum, pageSize);
27  
28     request.setAttribute("albums", albums);
29     request.setAttribute("pageNum", pageNum);
30     
31     int rows = albumItem.getRowCountWithGenreid(Integer.valueOf(id));
32     int pageCount = (int)Math.ceil((double)rows/pageSize);
33    // int pageCount =albumItem.getRowCountWithGenreid(Integer.valueOf(id));
34     request.setAttribute("pageCount", pageCount);
35     
36     request.setAttribute("genreId", id);
37     
38   
39    %>
40   
41   <body>
42     <div id="wrapper">
43             <%@ include file="shared/front_header.jsp" %>
44         <div id="content">
45             <%@ include file="shared/front_sidebar.jsp" %>
46             <div id="main">
47                 <h3 id="main-title">唱片列表</h3>
48                 <c:forEach var="album" items="${albums}">
49                    <table class="albumItem">
50                        <tr>
51                            <td rowspan="3" class="albumItem-image"><img src="CoverImages/${album.id}.jpg" alt="" /></td>
52                            <td colspan="2" class="albumItem-title">
53                                <a href="album.jsp?albumId=${album.id}">${album.title}</a>
54                            </td>
55                        </tr>
56                        <tr>
57                            <td class="albumItem-artist"><strong>歌手：${album.artist }</strong></td>
58                            <td class=".albumItem-price"><strong>定价：${album.price }</strong>￥</td>
59                        </tr>
60                        <tr>
61                            <td colspan="2">
62                             ${album.description}
63                            </td>
64                        </tr>
65                    </table>    
66                 </c:forEach>
67                 <hr/>
68                   
69                    <a href="album_list.jsp?page=1&genreId=${genreId}&title=${title}">第一页</a>
70                    <c:if test="${pageNum>1 }">
71                     <a href="album_list.jsp?page=${pageNum-1}&genreId=${genreId}&title=${title}">上一页</a>
72          
73                   </c:if>
74                   <c:if test="${pageNum<pageCount}">
75                     <a href="album_list.jsp?page=${pageNum+1}&genreId=${genreId}&title=${title}">下一页</a>
76                 </c:if>
77                    <a href="album_list.jsp?page=${pageCount}&genreId=${genreId}&title=${title}">最后一页</a>
78                     &nbsp;共${pageCount}页，第${pageNum}页。
79                 
80             </div>
81             <div class="clearBoth"></div>
82         </div>
83         <%@ include file="shared/front_footer.jsp" %>
84     </div>
85   </body>
86 </html>

 

对于分页，前面的博客有讲述，就不赘述了~

 

 说实话，今天我好累了~就写那么多吧~现在距离下课还有5分钟，我要记会儿单词~