Question

如何使用数据库中的值插入组合框我想从数据库中选择并添加组合框我有两节课：

构造函数Database（）第一类

//constructeur 
Database()   
                  {  

 void remplir_Jcomb() {
           Connection conn = null;
           Statement  st = null;
           String rq1 = "SELECT region  FROM  rg";
           String rq2 = "SELECT ACTELS  FROM  rg";

        // - Paramètres de connexion à la base de données
           String url = "jdbc:mysql://localhost/réseau";
           String login = "root";
           String password = "";
           String driver = "com.mysql.jdbc.Driver";

           try {

            //comboBox_gouver.removeAllItems();
               try {
                    Class.forName(driver);
                    conn = DriverManager.getConnection(url,login,password);
                    } catch (ClassNotFoundException e) {
                        e.printStackTrace();
                         }

               st = conn.createStatement();
               ResultSet rs1 = st.executeQuery(rq1);
               ResultSet rs2 = st.executeQuery(rq2);

               while ((rs1.next())&&(rs2.next())) {
                comboBox_gouver.addItem(rs1.getString(1));
                comboBox_ACTELS.addItem(rs2.getString(1));
               }
               st.close();
               rs1.close();
               rs2.close();
               conn.close();

           }  catch (SQLException e) { 
                e.printStackTrace();}

            }
        }

界面摆动第二类，其中包含两个JComboBox 调用构造函数Database（）

private Database BD= new Database();  
    public Region() {


//first JComboBox
    comboBox_gouver = new JComboBox<String>();
            BD.remplir_Jcomb();
                sl_contentPanel.putConstraint(SpringLayout.NORTH, lbl_gouver, 5, SpringLayout.NORTH, comboBox_gouver);
                sl_contentPanel.putConstraint(SpringLayout.NORTH, comboBox_gouver, 5, SpringLayout.NORTH, contentPanel);
                sl_contentPanel.putConstraint(SpringLayout.WEST, comboBox_gouver, 16, SpringLayout.EAST, lbl_gouver);
                sl_contentPanel.putConstraint(SpringLayout.EAST, comboBox_gouver, -26, SpringLayout.EAST, contentPanel);
                contentPanel.add(comboBox_gouver);

comboBox_ACTELS = new JComboBox<String>();
        sl_contentPanel.putConstraint(SpringLayout.NORTH, lbl_ACTELS, 5, SpringLayout.NORTH, comboBox_ACTELS);
        sl_contentPanel.putConstraint(SpringLayout.NORTH, comboBox_ACTELS, 6, SpringLayout.SOUTH, comboBox_gouver);
        sl_contentPanel.putConstraint(SpringLayout.WEST, comboBox_ACTELS, 90, SpringLayout.EAST, lbl_ACTELS);
        sl_contentPanel.putConstraint(SpringLayout.SOUTH, comboBox_ACTELS, -29, SpringLayout.SOUTH, contentPanel);
        sl_contentPanel.putConstraint(SpringLayout.EAST, comboBox_ACTELS, -26, SpringLayout.EAST, contentPanel);
        contentPanel.add(comboBox_ACTELS);
}}

ERREUR：

java.sql.SQLException: Operation not allowed after ResultSet closed
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927)
    at com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:794)
    at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:7139)
    at tn.pack.ACTEL.Database.remplir_Jcomb(Database.java:94)
    at tn.pack.ACTEL.Region.<init>(Region.java:75)
    at tn.pack.ACTEL.Region.main(Region.java:41)

Answer 1

1）从Db填充数据（使用finally block关闭已打开的对象，因为此代码在所有情况下都会执行）

void whatever {

   Connection conn = null;
   Statement  st1 = null;

   try {
       st1 = conn.createStatement();

   }  catch (SQLException e) { 
      e.printStackTrace();
   }  finally { 
      try {
          st1.close();
          rs1.close();
          rs2.close();
          conn.close();
      } catch (SQLException ex) {
          //
      } 
   }
}

2）在Db Statement填充数据中（注意到Java6 / Java7之间API的差异），

到ComboBoxModel - JComboBox(ComboBoxModel aModel)/JComboBox(ComboBoxModel<E> aModel)
到arrays of Objects/Elements - JComboBox(Object[] items)/JComboBox(E[] items)
到Vector of Objects/Elements - JComboBox(Vector items)/JComboBox(Vector<E> items)

如果Sql块结束，则将数组类型添加到JComboBox

编辑：

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import javax.swing.*;

public class ComboBoxListeners {

    private JFrame f;
    private JComboBox comboBox;
    private JLabel label = new JLabel();
    private DefaultComboBoxModel comboBoxModel = new DefaultComboBoxModel();

    public ComboBoxListeners() {
        comboBox = new JComboBox(comboBoxModel);
        comboBox.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                if ((e.getStateChange() == ItemEvent.SELECTED)) {
                    String str = comboBox.getSelectedItem().toString();
                    label.setText("Selected Value From JComboBox is :   " + str);
                }
            }
        });
        label.setPreferredSize(new Dimension(400, 30));
        JButton btnAdd = new JButton(new AbstractAction("Append Items") {

            private static final long serialVersionUID = 1L;

            @Override
            public void actionPerformed(ActionEvent e) {
                addNewItemsFromDatabase();
            }
        });
        JButton btnRefresh = new JButton(new AbstractAction("Refresh Items") {

            private static final long serialVersionUID = 1L;

            @Override
            public void actionPerformed(ActionEvent e) {
                refreshItemsFromDatabase();
            }
        });
        f = new JFrame("ComboBox ItemListeners");
        f.setLayout(new GridLayout(0, 1, 15, 15));
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(comboBox);
        f.add(label);
        f.add(btnAdd);
        f.add(btnRefresh);
        f.setLocation(150, 150);
        f.pack();
        f.setVisible(true);
    }

    public void addNewItemsFromDatabase() {
        ArrayList<Integer> ageList = new ArrayList<Integer>();
        for (int i = 1; i <= 5; ++i) {
            ageList.add(i);
        }
        for (final Integer i : ageList) {
            EventQueue.invokeLater(new Runnable() {

                public void run() {// updates to the Swing GUI must be done on EDT
                    comboBoxModel.addElement(i);
                }
            });
        }
    }

    public void refreshItemsFromDatabase() {
        comboBoxModel = new DefaultComboBoxModel();
        ArrayList<Integer> ageList = new ArrayList<Integer>();
        for (int i = 1; i <= 5; ++i) {
            ageList.add(i);
        }
        for (final Integer i : ageList) {
            EventQueue.invokeLater(new Runnable() {

                public void run() {// updates to the Swing GUI must be done on EDT
                    comboBoxModel.addElement(i);
                }
            });
        }
        comboBox.setModel(comboBoxModel);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                ComboBoxListeners comboBoxListeners = new ComboBoxListeners();
            }
        });
    }
}

Answer 2

为两个ResultSet对象使用两个单独的Statement对象。当Statement对象已经打开并由ResultSet使用时，您无法重用它。这样的事情： -

void remplir_Jcomb() {
       Connection conn = null;
       Statement  st1 = null;
       Statement  st2 = null;
       String rq1 = "SELECT region  FROM  rg";
       String rq2 = "SELECT ACTELS  FROM  rg";

       //Rest of your code here

       try {

          // snipping off some more code
          //...

           st1 = conn.createStatement();
           st2 = conn.createStatement();
           ResultSet rs1 = st1.executeQuery(rq1);
           ResultSet rs2 = st2.executeQuery(rq2);

           while ((rs1.next())&&(rs2.next())) {
            comboBox_gouver.addItem(rs1.getString(1));
            comboBox_ACTELS.addItem(rs2.getString(1));
           }

       }  catch (SQLException e) { 
            e.printStackTrace();
       }
       finally{
           st1.close();
           st1.close();
           rs1.close();
           rs2.close();
           conn.close();
       }

    }

如何用数据库中的值填充组合框？

2 个答案: