无法使用JList显示来自数据库的结果

Question

This got to be an easy fix. I have been trying all day yesterday, and I cannot get this thing working.I cannot fetch data from a database and show it in a JList. Normally, I separate the classes in different files, but for the purpose of me to learn Java, I put everything in one file.

public class Window extends JFrame{
private static final long serialVersionUID = 1L;

// declare global text fields
private JTextField txtCustomerID;
private JTextField txtFirstName;
private JTextField txtLastName;
private JTextField txtMiddleInitial;
private JTextField txtStreet;
private JTextField txtCity;
private JTextField txtState;
private JTextField txtZip;
private JTextField txtPhone;
private JTextField txtEmail;
private JTextField txtSearch;

// declare global list
private static JList list;
private String[] results;
private DefaultListModel model;

// declare global labels
private JLabel labFirstName;
private JLabel labLastName;
private JLabel labMiddleInitial;
private JLabel labStreet;
private JLabel labCity;
private JLabel labState;
private JLabel labZip;
private JLabel labPhone;
private JLabel labEmail;

// declare global buttons
private JButton newCustomer;
private JButton open;
private JButton update;
private JButton cancel;
private JButton remove;
private JButton search;

// function that adds components to GridBagConstraints Layout Manager
private void addComponent(JPanel panel, JComponent theComponent, int xPos, int yPos, int compWidth, int compHeight, int place, int stretch, boolean useScrollPane){
    GridBagConstraints gbc = new GridBagConstraints();
    gbc.gridx = xPos;
    gbc.gridy = yPos;
    gbc.gridwidth = compWidth;
    gbc.gridheight = compHeight;
    gbc.weightx = 100;
    gbc.weighty = 100;
    gbc.insets = new Insets(2,2,2,2);
    gbc.anchor = place;
    gbc.fill = stretch;
    if(useScrollPane){
        JScrollPane scrollPane = new JScrollPane(theComponent);
        scrollPane.setPreferredSize(new Dimension(400, 200));
        panel.add(scrollPane, gbc);
    } else {
        panel.add(theComponent, gbc);
    }

}

// function that adds components to panel
private void addComponent2(JPanel panel, JComponent theComponent){
    panel.add(theComponent);
}


// function that connects and tests to the database
private void insertDatabase(){

    try {

        Connection connect = null;

        Class.forName("com.mysql.jdbc.Driver");

        String url = "";
        String user = "";
        String password ="";

        connect = DriverManager.getConnection(url,user,password);

        Statement SQLStatement = connect.createStatement();
        String insert = "INSERT INTO customerinfo(FirstName," +
                "LastName, MiddleInitial, Street, City, State, ZipCode, Phone, Email) VALUES('"+ txtFirstName.getText() +"', " +
                        "'" + txtLastName.getText() +"', '" + txtMiddleInitial.getText() +"', '" + txtStreet.getText() +"', " +
                                "'" + txtCity.getText() +"', '" + txtState.getText() +"', '" + Integer.parseInt(txtZip.getText()) +"'" +
                                ", '" + txtPhone.getText() +"', '" + txtEmail.getText() +"')";
        SQLStatement.execute(insert);

        connect.close();

    } catch (ClassNotFoundException e) {
        JOptionPane.showMessageDialog(this, "Where is your Mysql JDBC Driver?");
        e.printStackTrace();
    } catch (SQLException e){
        JOptionPane.showMessageDialog(this, "SQLException: " + e.getMessage());
        JOptionPane.showMessageDialog(this, "VendorError: " + e.getErrorCode());
    }

}


// function that checks for empty fields
private void checkForEmptyFields(){

    String[] labValues = {labFirstName.getText(), labLastName.getText(), labMiddleInitial.getText(),
            labStreet.getText(), labCity.getText(), labState.getText(), labZip.getText(), 
            labPhone.getText(), labEmail.getText()};

    String[] values = {txtFirstName.getText(), txtLastName.getText(),
            txtMiddleInitial.getText(), txtStreet.getText(), txtCity.getText(),
            txtState.getText(), txtZip.getText(), txtPhone.getText(), txtEmail.getText()};

    for(int i=0; i<values.length; i++){
        if(values[i].length() == 0){
            JOptionPane.showMessageDialog(this, labValues[i].replace(":", "") + " field is empty");
        }
    }

}

// function that will update a field in the database
private void updateDatabase(){
    try {

        Connection connect = null;

        Class.forName("com.mysql.jdbc.Driver");

        String url = "";
        String user = "";
        String password ="";

        connect = DriverManager.getConnection(url,user,password);

        Statement SQLStatement = connect.createStatement();
        String update = "UPDATE customerinfo SET FirstName='" + txtFirstName.getText() +"', LastName='" + txtLastName.getText() +"', " +
                "MiddleInitial='"+ txtMiddleInitial.getText() +"', Street='"+ txtStreet.getText() +"', City='"+ txtCity.getText() +"', " +
                "State='"+ txtState.getText() +"', ZipCode='"+ txtZip.getText() +"', Phone='"+ txtPhone.getText() +"', " +
                "Email='"+ txtEmail.getText() +"'" +
                "WHERE CustomerID='"+ txtCustomerID.getText() +"'";
        SQLStatement.execute(update);

    } catch (ClassNotFoundException e) {
        JOptionPane.showMessageDialog(this, "Where is your Mysql JDBC Driver?");
        e.printStackTrace();
    } catch (SQLException e){
        JOptionPane.showMessageDialog(this, "SQLException: " + e.getMessage());
        JOptionPane.showMessageDialog(this, "VendorError: " + e.getErrorCode());
    }
}

// function that will delete a record from the database
private void deleteRecord(){
    try {

        Connection connect = null;

        Class.forName("com.mysql.jdbc.Driver");

        String url = "";
        String user = "";
        String password ="";

        connect = DriverManager.getConnection(url,user,password);

        Statement SQLStatement = connect.createStatement();
        String delete = "DELETE FROM customerinfo WHERE CustomerID='"+ txtCustomerID.getText() +"'";
        SQLStatement.execute(delete);

        connect.close();

    } catch (ClassNotFoundException e) {
        JOptionPane.showMessageDialog(this, "Where is your Mysql JDBC Driver?");
        e.printStackTrace();
    } catch (SQLException e){
        JOptionPane.showMessageDialog(this, "SQLException: " + e.getMessage());
        JOptionPane.showMessageDialog(this, "VendorError: " + e.getErrorCode());
    }
}

// function that will search for records in the database
private void searchRecord(){

    model = new DefaultListModel();
    list = new JList(model);
    list.setVisibleRowCount(3);
    list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    //list.setFixedCellHeight(27);
    //list.setFixedCellWidth(130);

    try {

        model.clear();

        Connection connect = null;

        Class.forName("com.mysql.jdbc.Driver");

        String url = "";
        String user = "";
        String password ="";

        connect = DriverManager.getConnection(url,user,password);

        Statement SQLStatement = connect.createStatement();
        String select = "SELECT * FROM customerinfo WHERE LastName LIKE '"+ txtSearch.getText().trim() +"%'";
        ResultSet rows = SQLStatement.executeQuery(select);

        while(rows.next()){
            model.addElement(rows.getString("FirstName") + "\n");
            System.out.print(model.toString() + "\n");
        }


            System.out.print(model.getSize());
            rows.close();
            SQLStatement.close();
            connect.close();

            txtSearch.setText("");

    } catch (ClassNotFoundException e) {
        JOptionPane.showMessageDialog(this, "Where is your Mysql JDBC Driver?");
        e.printStackTrace();
    } catch (SQLException e){
        JOptionPane.showMessageDialog(this, "SQLException: " + e.getMessage());
        JOptionPane.showMessageDialog(this, "VendorError: " + e.getErrorCode());
    }

}

// function that clear fields once register
private void clearFields(){
    txtFirstName.setText("");
    txtLastName.setText("");
    txtMiddleInitial.setText("");
    txtStreet.setText("");
    txtCity.setText("");
    txtState.setText("");
    txtZip.setText("");
    txtPhone.setText("");
    txtEmail.setText("");
}

// Implement Action Listener
private class handler implements ActionListener{

    @Override
    public void actionPerformed(ActionEvent e) {
        // if user clicks on New Customer Button, do the following...
        if(e.getSource() == newCustomer){
            checkForEmptyFields();
            insertDatabase();
            clearFields();
        } else if(e.getSource() == update){
            checkForEmptyFields();
            updateDatabase();
            clearFields();
        } else if(e.getSource() == remove){
            checkForEmptyFields();
            deleteRecord();
            clearFields();
        } else if(e.getSource() == cancel){
            clearFields();
        } else if(e.getSource() == open){

        } else if(e.getSource() == search){
            searchRecord();
        } 

    }

}

private class selectRow implements ListSelectionListener{

    @Override
    public void valueChanged(ListSelectionEvent event) {
        if(!event.getValueIsAdjusting()){
            String selection = list.getSelectedValue().toString();
        }

    }

}

// window constructor
public Window(){

    JPanel theMainPanel = new JPanel(new BorderLayout());

    JPanel thePanel = new JPanel();
    thePanel.setLayout(new GridBagLayout());

    JTabbedPane tabbedPane = new JTabbedPane();


    JLabel labCustomerID = new JLabel("Customer ID:");
    addComponent(thePanel, labCustomerID, 0, 0, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtCustomerID = new JTextField(24);
    txtCustomerID.setEnabled(false);
    txtCustomerID.setBackground(Color.LIGHT_GRAY);
    addComponent(thePanel, txtCustomerID, 1, 0, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    open = new JButton("Open");
    addComponent(thePanel, open, 1, 0, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);

    labFirstName = new JLabel("First Name:");
    addComponent(thePanel, labFirstName, 0, 1, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtFirstName = new JTextField(30);


    addComponent(thePanel, txtFirstName, 1, 1, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    labLastName = new JLabel("Last Name:");
    addComponent(thePanel, labLastName, 0, 3, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtLastName = new JTextField(30);
    addComponent(thePanel, txtLastName, 1, 3, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    labMiddleInitial = new JLabel("Middle Initial:");
    addComponent(thePanel, labMiddleInitial, 0, 4, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtMiddleInitial = new JTextField(30);
    addComponent(thePanel, txtMiddleInitial, 1, 4, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    labStreet = new JLabel("Street:");
    addComponent(thePanel, labStreet, 0, 5, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtStreet = new JTextField(30);
    addComponent(thePanel, txtStreet, 1, 5, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    labCity = new JLabel("City:");
    addComponent(thePanel, labCity, 0, 6, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtCity = new JTextField(30);
    addComponent(thePanel, txtCity, 1, 6, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    labState = new JLabel("State:");
    addComponent(thePanel, labState, 0, 7, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtState = new JTextField(30);
    addComponent(thePanel, txtState, 1, 7, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    labZip = new JLabel("Zip Code:");
    addComponent(thePanel, labZip, 0, 8, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtZip = new JTextField(5);
    addComponent(thePanel, txtZip, 1, 8, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    labPhone = new JLabel("Phone:");
    addComponent(thePanel, labPhone, 0, 9, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtPhone = new JTextField(30);
    addComponent(thePanel, txtPhone, 1, 9, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    labEmail = new JLabel("Email:");
    addComponent(thePanel, labEmail, 0, 10, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtEmail = new JTextField(30);
    addComponent(thePanel, txtEmail, 1, 10, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    this.add(thePanel, BorderLayout.NORTH);

    JPanel thePanel2 = new JPanel();
    thePanel2.setLayout(new FlowLayout(FlowLayout.RIGHT));
    newCustomer = new JButton("New Customer");
    addComponent2(thePanel2, newCustomer);
    update = new JButton("Update");
    addComponent2(thePanel2, update);
    remove = new JButton("Remove");
    addComponent2(thePanel2, remove);
    cancel = new JButton("Cancel");
    addComponent2(thePanel2, cancel);
    this.add(thePanel2, BorderLayout.CENTER);

    JPanel thePanel3 = new JPanel(new GridBagLayout());
    thePanel3.setBorder(BorderFactory.createTitledBorder("Customer Action"));
    JLabel labSearch = new JLabel("Search By Last Name:");
    addComponent(thePanel3, labSearch, 0, 0, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    txtSearch = new JTextField(15);
    addComponent(thePanel3, txtSearch, 1, 0, 1, 1, GridBagConstraints.WEST, GridBagConstraints.NONE, false);
    search = new JButton("Search");
    addComponent(thePanel3, search, 2, 0, 1, 1, GridBagConstraints.EAST, GridBagConstraints.NONE, false);
    //JScrollPane scrollPane = new JScrollPane(list);
    //scrollPane.setPreferredSize(new Dimension(400,200));
    addComponent(thePanel3, list, 0, 1, 3, 1, GridBagConstraints.CENTER, GridBagConstraints.NONE, true);
    this.add(thePanel3, BorderLayout.SOUTH);


    theMainPanel.add(thePanel, BorderLayout.NORTH);
    theMainPanel.add(thePanel2, BorderLayout.CENTER);
    theMainPanel.add(thePanel3, BorderLayout.SOUTH);



    tabbedPane.addTab("Customer Info", theMainPanel);
    this.add(tabbedPane);


    handler listen = new handler();
    newCustomer.addActionListener(listen);
    update.addActionListener(listen);
    remove.addActionListener(listen);
    cancel.addActionListener(listen);
    search.addActionListener(listen);



}


}

Answer 1

Do list = new JList(model); at the end, with the model filled.

---

* Another attempt: This time with first().

private void searchRecord() {

    model = new DefaultListModel();
    try {
        Connection connect = null;

        Class.forName("com.mysql.jdbc.Driver");

        String url = "";
        String user = "";
        String password ="";

        connect = DriverManager.getConnection(url,user,password);

        Statement sqlStatement = connect.createStatement();
        String select = "SELECT FirstName, LastName "
            + "FROM customerinfo WHERE LastName LIKE '" +  txtSearch.getText().trim() + "%' "
            + "ORDER BY FirstName, LastName";
        ResultSet rows = sqlStatement.executeQuery(select);

        if (rows.first()) {
            do {
                model.addElement(rows.getString("FirstName"));
            } while (rows.next());
        }

        rows.close();
        sqlStatement.close();
        connect.close();

        txtSearch.setText("");

        list = new JList(model);
        list.setVisibleRowCount(3);
        list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    } catch (ClassNotFoundException e) {
        JOptionPane.showMessageDialog(this, "Where is your Mysql JDBC Driver?");
        e.printStackTrace();
    } catch (SQLException e){
        JOptionPane.showMessageDialog(this, "SQLException: " + e.getMessage());
        JOptionPane.showMessageDialog(this, "VendorError: " + e.getErrorCode());
    }

}

Answer 2

1. verify that the SQL portion works correctly. Try a System.out.println() in the while(rows.next()) loop.
2. After the loop completes, query the model for its size. If it is zero, you have a problem.
3. If the model is not empty, but the JList doesn't show anything, verify that the model actually fires the correct events (it should, since you are using unchanged DefaultListModel, but in custom implementations you might forget to fire the events) when data changes. For this you can add a ListModelListener to the model and have it print out whenever an event is fired.
4. Check the JList itself. Is it disabled? Are you doing anything to it that would prevent it from displaying data? Strip off any customization code and start with a plain panel.add(new JList(myModel)) and go from there.