这必须很容易解决。我昨天已经尝试了一整天，我无法让这个东西工作。我无法从数据库中获取数据并将其显示在 JList 中。通常，我将类分开在不同的文件中，但为了学习Java，我将所有内容放在一个文件中。
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);
}
}
- 验证 SQL 部分是否正常工作。在
while(rows.next())循环中尝试 System.out.println（）。 - 循环完成后，查询模型的大小。如果为零，则有问题。
- 如果模型不为空，但 JList 未显示任何内容，请验证模型在数据更改时是否实际触发了正确的事件（它应该触发，因为您使用的是未更改的 DefaultListModel，但在自定义实现中，您可能会忘记触发事件）。为此，您可以向模型添加一个 ListModelListener，并在触发事件时将其打印出来。
- 检查 JList 本身。是否禁用？您是否对它做了任何会阻止它显示数据的事情？剥离任何自定义代码，从普通
panel.add(new JList(myModel))开始，然后从那里开始。
最后执行list = new JList(model);，并填充模型。
*另一次尝试：这次使用 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());
}
}