Ich habe eine Tabelle namens "Benutzer", aus dem ich die Benutzertypen in einer Combo-Box anzeigen möchte. Ich habe eine separate Klasse für die Verbindung erstellt.Daten nicht in Combobox - Sql und Java mit Netbeans
package testdb;
import java.sql.*;
import javax.swing.*;
public class MySqlConnect {
Connection conn = null;
public static Connection ConnectDB(){
try{
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "");
JOptionPane.showMessageDialog(null, "Connected to database");
return conn;
}
catch (Exception e){
JOptionPane.showMessageDialog(null, e);
return null;
}
}
}
Das Formular, auf dem ich das Kombinationsfeld erstellt habe, hat den folgenden Code.
package testdb;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.swing.JOptionPane;
public class Combo extends javax.swing.JFrame {
Connection conn = null;
PreparedStatement pst = null;
ResultSet rs = null;
public Combo() {
initComponents();
}
private void initComponents() {
jLabel1 = new javax.swing.JLabel();
combo1 = new javax.swing.JComboBox<>();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jLabel1.setText("User Type");
combo1.setModel(new javax.swing.DefaultComboBoxModel<>(new String[] { "Item 1", "Item 2", "Item 3", "Item 4" }));
combo1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
combo1ActionPerformed(evt);
}
});
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(41, 41, 41)
.addComponent(jLabel1)
.addGap(73, 73, 73)
.addComponent(combo1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(181, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(43, 43, 43)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel1)
.addComponent(combo1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addContainerGap(237, Short.MAX_VALUE))
);
pack();
}// </editor-fold>
private void combo1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
try{
conn = MySqlConnect.ConnectDB();
String s = "Select * from user";
pst = conn.prepareStatement(s);
rs = pst.executeQuery();
while(rs.next()){
String cb = rs.getString("username");
combo1.addItem(cb);
}
}
catch (Exception e){
JOptionPane.showMessageDialog(null, e);
}
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(Combo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(Combo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(Combo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(Combo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new Combo().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JComboBox<String> combo1;
private javax.swing.JLabel jLabel1;
// End of variables declaration
}
Das Kombinationsfeld zeigt immer noch keine Werte aus der Datenbank an. Könnte mir bitte jemand sagen, was in meinem Code nicht stimmt?