Java JDBC Eclipse Populate JTable with Oracle DB

Question

so I am working to create a functioning GUI that can retrieve info from a database (in this case I'm using Oracle 11g XE) using JDBC to do things such as populate a JTable (built using WindowBuilder).

My Oracle DB Server is running and I can successfully connect to it, however when I try and execute a query to be passed to the DB something goes wrong.

Here is my Connection class, just used to connect to the DB:

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();
  }
}

This works (at least to my knowledge it is because I am prompted with a "Connection Successful!" message)

Now here my GUI class (only other class at the moment):

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();
    }
  }
}  

It seems to break on pat = conn.prepareStatement(query);

The error I am getting is...

at Management.generateDownloads(Management.java:207) at Management.access$1(Management.java:204) at Management$2.actionPerformed(Management.java:115) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$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)...

and continues on for many more lines of similar errors..

I can't seem to figure out any reason why it is not properly communicating with the DB. Any help would be GREATLY appreciated guys!

Answer 1

But your dbConnector() method always returns null.

Perhaps you want it to do this instead:

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;
}