Java JDBC Eclipse 使用 Oracle DB 填充 JTable

Question

所以我正在努力创建一个功能性的 GUI，它可以使用 JDBC to do things such as populate a JTable (built using WindowBuilder 从数据库中检索信息（在本例中我使用的是 Oracle 11g XE）。

我的 Oracle 数据库服务器是运行，我可以成功连接到它，但是当我尝试执行要传递给数据库的查询时，出现了问题。

这是我的连接 class，只是用来连接到数据库：

import java.sql.*;
import javax.swing.*;

public class OracleConnection {
  static Connection con = null;

  public static Connection dbConnector() {
    try {
      Class.forName("oracle.jdbc.driver.OracleDriver");
      con = DriverManager.getConnection(
          "jdbc:oracle:thin:@localhost:1521:XE", "system", "system");
      JOptionPane.showMessageDialog(null, "Connection Successful!");
    } catch (Exception x) {
      JOptionPane.showMessageDialog(null, "Connection Unsuccessful.");
    }
    return null;
  }

  public static void main(String[] args) {
    dbConnector();
  }
}

这有效（至少据我所知，这是因为系统提示我 "Connection Successful!" 消息）

现在我的 GUI class（目前只有其他 class）：

import java.awt.EventQueue;
import java.sql.*;
import javax.swing.*;
import java.awt.CardLayout;
import javax.swing.JPanel;
import javax.swing.JButton;
import java.awt.Font;
import javax.swing.JLabel;
import javax.swing.JTable;
import javax.swing.JScrollPane;
import javax.swing.table.DefaultTableModel;

import net.proteanit.sql.DbUtils;

import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Management {

  private JFrame frame;
  private JTable tableDownloads;
  private JPanel panelMenu;
  private JPanel panelDown;
  private JPanel panelUp;
  private JPanel panelUtility;
  private JTable tableUploads;
  private JTable tableUtilities;
  ResultSet rs = null;
  PreparedStatement pat = null;
  Connection conn = null;


  /**
   * Launch the application.
   */
  public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
      public void run() {
        try {
          Management window = new Management();
          window.frame.setVisible(true);
        } catch (Exception e) {
          e.printStackTrace();
        }
      }
    });
  }

  /**
   * Create the application.
   */

  public Management() {
    conn = OracleConnection.dbConnector();
    initialize();
  }

  /**
   * Initialize the contents of the frame.
   */
  private void initialize() {

    //CREATES ALL FRAMES / PANELS / BUTTONS / SCROLLPANES / LABELS
    //I CUT A LOT OF UN-NEEDED STUFF OUT TO SAVE ROOM

    //CREATING FRAMES
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(new CardLayout(0, 0));


    //CREATING PANELS
    final JPanel panelMenu = new JPanel();
    frame.getContentPane().add(panelMenu, "name_13312291634045");
    panelMenu.setLayout(null);

    final JPanel panelDown = new JPanel();
    frame.getContentPane().add(panelDown, "name_13314999633769");
    panelDown.setLayout(null);
    panelDown.setVisible(false);


    //CREATING TABLES
    tableDownloads = new JTable();
    scrollPaneDownloads.setViewportView(tableDownloads);


    //CREATING BUTTONS
    JButton btnDownloads = new JButton("Downloads");
    btnDownloads.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent arg0) {
        panelMenu.setVisible(false);
        panelDown.setVisible(true);
        generateDownloads();
      }
    });
    btnDownloads.setFont(new Font("Cambria", Font.BOLD, 14));
    btnDownloads.setBounds(32, 104, 122, 39);
    panelMenu.add(btnDownloads);

    JButton btnBackDown = new JButton("Back to Menu");
    btnBackDown.setFont(new Font("Cambria", Font.PLAIN, 13));
    btnBackDown.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        panelDown.setVisible(false);
        panelMenu.setVisible(true);
      }
    });
    btnBackDown.setBounds(323, 239, 109, 23);
    panelDown.add(btnBackDown);


    //CREATING LABELS
    JLabel lblDownloaduploadAndUtility = new JLabel("Download/Upload and Utility Manager");
    lblDownloaduploadAndUtility.setFont(new Font("Cambria", Font.BOLD, 20));
    lblDownloaduploadAndUtility.setBounds(48, 11, 370, 39);
    panelMenu.add(lblDownloaduploadAndUtility);

    JLabel lblDownloadsTable = new JLabel("Downloads Table");
    lblDownloadsTable.setFont(new Font("Cambria", Font.BOLD, 24));
    lblDownloadsTable.setBounds(122, 0, 196, 29);
    panelDown.add(lblDownloadsTable);
  }


  //METHOD TO GENERATE DOWNLOADS TABLE ******NOT WORKING******

  private void generateDownloads() {
    try {
      String query = "SELECT * FROM DOWNLOADS";
      pat = conn.prepareStatement(query);     //******** FAILS HERE ********
      rs = pat.executeQuery();
      tableDownloads.setModel(DbUtils.resultSetToTableModel(rs));
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

好像在pat = conn.prepareStatement(query);

上断了

我收到的错误是...

at Management.generateDownloads(Management.java:207) at Management.access(Management.java:204) at Management.actionPerformed(Management.java:115) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)...

并继续更多类似错误的行..

我似乎无法找出它无法与数据库正确通信的任何原因。任何帮助将不胜感激！

Answer 1

但是你的dbConnector()方法总是returns null。

也许您希望它这样做：

public static Connection dbConnector() {
    if (con == null) {
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
            con = DriverManager.getConnection(
                "jdbc:oracle:thin:@localhost:1521:XE", "system", "system");
            JOptionPane.showMessageDialog(null, "Connection Successful!");
        } catch (Exception x) {
            JOptionPane.showMessageDialog(null, "Connection Unsuccessful.");
        }
    }
    return con;
}

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