数据检索 - JDBC与Eclipse

Question

我试图从我的数据库检索数据。它是PHP MyAdmin数据库（MySQL）。这里是我写的代码：

package dto; 

import java.sql.Timestamp; 

public class Pictures { 

int idPicture; 
String longitude; 
String latitude; 
int status; 
String path; 
Timestamp timestamp; 

/* 
* Constructor for a picture 
*/ 
public Pictures(int idPicture, 
String longitude, 
String latitude, 
int status, 
String path, 
Timestamp timestamp){ 

    this.idPicture = idPicture; 
    this.longitude = longitude; 
    this.latitude = latitude; 
    this.status = status; 
    this.path = path; 
    this.timestamp = timestamp; 


} 

public int getIdPicture() { 
    return idPicture; 
} 

public void setIdPicture(int idPicture) { 
    this.idPicture = idPicture; 
} 

public String getLongitude() { 
    return longitude; 
} 

public void setLongitude(String longitude) { 
    this.longitude = longitude; 
} 

public String getLatitude() { 
    return latitude; 
} 

public void setLatitude(String latitude) { 
    this.latitude = latitude; 
} 

public int getStatus() { 
    return status; 
} 

public void setStatus(int status) { 
    this.status = status; 
} 

public String getPath() { 
    return path; 
} 

public void setPath(String path) { 
    this.path = path; 
} 

public Timestamp getTimestamp() { 
    return timestamp; 
} 

public void setTimestamp(Timestamp timestamp) { 
    this.timestamp = timestamp; 
} 

} 

上面是我有我的照片的课。

package dao; 

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

import dto.Pictures; 

public class Storingdb { 

private static final String url = "jdbc:mysql://localhost/internship"; 
private static final String username = "root"; 
private static final String password = ""; 


public Storingdb() { 

} 
/* 
* Connection method 
*/ 
private Connection connect() { 

    Connection connexion; 

    try { 
     Class.forName("com.mysql.jdbc.Driver"); 
    } catch (ClassNotFoundException cnfe) { 
     System.err.println("Error loading driver: " + cnfe); 
    } 
    // Connection to the database 
    try { 
     connexion = DriverManager.getConnection(url, username, password); 
     return connexion; 
    } catch (SQLException e) { 
     e.printStackTrace(); 
    } 

    return null; 
} 

public Pictures retrieveData() { 

    Pictures pic = null; 

    int idPicture = 0; 
    String longitude = null; 
    String latitude = null; 
    int status = 0; 
    String path = null; 
    Timestamp timestamp = null; 

    Connection connexion = connect(); 
    PreparedStatement ps = null; 
    ResultSet rs = null; 

    try { 
     ps = connexion.prepareStatement("SELECT * FROM storing WHERE id=1"); 
     rs = ps.executeQuery(); 
     pic = new Pictures(idPicture, longitude, latitude, status, path, timestamp); 


     while (rs.next()) { 
      pic.setIdPicture(rs.getInt(1)); 
      longitude = rs.getString(2); 
      latitude = rs.getString(3); 
      status = rs.getInt(4); 
      path = rs.getString(5); 
      timestamp = rs.getTimestamp(6); 



     } 
    } catch (SQLException e) { 

     e.printStackTrace(); 

    } finally { 
     try { 
      ps.close(); 
     } catch (SQLException e1) { 
      e1.printStackTrace(); 
     } 
     try { 
      connexion.close(); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 

    return pic; 
} 
} 

以上是DAO类。

<div> 
    <% 
    Storingdb dao = new Storingdb(); 
    //ArrayList<Pictures> file = new ArrayList<Pictures>(); 
    //file = dao.retrieveData(); 

    Pictures pic; 
    pic = dao.retrieveData(); 


    String empty = ""; 
    if(pic.getStatus() == 0) { 
     empty = "Empty"; 
    } else { 
     empty = "Taken"; 
    } 



    %> 

    <table class="table table-bordered"> 
     <thead> 
      <tr> 
       <th>Parking Space ID</th> 
       <th>Longitude</th> 
       <th>Latitude</th> 
       <th>Status :</th> 
       <th>Update time :</th> 
      </tr> 
     </thead> 
     <tbody> 
      <tr> 
       <td><%= pic.getIdPicture() %></td> 
       <td><%= pic.getLongitude() %></td> 
       <td><%= pic.getLatitude() %></td> 
       <td><%= empty %></td> 
       <td><%= pic.getTimestamp() %></td> 
      </tr> 
     </tbody> 


    </table> 
</div> 

这里是我的JSP的HTML代码。

我的表对于除iD /状态以外的所有内容都返回null。 我不明白为什么。

在我的数据库中，iD是一个i​​nt（11），自动递增。 经度为VARCHAR（32） 纬度为VARCHAR（32） 状态为int（1） 路径为VARCHAR（32） timestamp是TIMESTAMP，在添加/更新数据时更新。

为什么它是空的任何提示？

我接受提示而不是直接回答，所以我可以尝试单独修复。随时给我建议，但如果你想给它的话我接受答案。

在此先感谢，我一直在寻找答案3小时，我绝望哈哈！

Answer 1

您刚刚从数据库中选择了记录，但未检索到它。

所以试图从数据库中遍历ResultSet并获得的记录，像下面的方法retrieveData

rs = ps.executeQuery(); 
// retrieve records from database here 
if(rs.next()) { 
    idPicture = rs.getInt(1); // here 1 is column index of column pictureId 
    longitude = rs.getString(2); // here 2 is column index of string longitude 
    latitude = rs.getString(3); 
    status = rs.getInt(4); 
    path = rs.getString(5); 
    timestamp = rs.getTimestamp(6); 
    pic = new Pictures(idPicture, longitude, latitude, status, path, timestamp); 
} else { 
    // there is no record with id 1. 
} 

希望这会有所帮助。