java - 数据检索 - 带有 Eclipse 的 JDBC

Question

我正在尝试从数据库中检索数据。它是 PHP MyAdmin 数据库 (MySQL)。这是我写的代码:

    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;
}

}

上面是我有照片的类(class)。

    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;
}
}

上面是 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>

这是我的 JSP 的 HTML 代码。

我的表除了 iD/状态之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 int(11)，自动递增。 经度为 VARCHAR(32) 纬度为 VARCHAR(32) 状态为 int(1) 路径是 VARCHAR(32) 时间戳是添加/更新数据时更新的 TIMESTAMP。

关于为什么它为空的任何提示？

我接受提示而不是直接答案，这样我就可以尝试单独修复。请随意给我建议，但如果你确实想给出答案，我会接受。

先谢谢了，我已经找了3个小时的答案了，我很绝望哈哈!

Answer 1

您只是从数据库中选择了记录，但尚未检索它。

因此，尝试迭代 ResultSet 并从数据库中获取记录，如下方法 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。