我正在开发一个程序(Java)，该程序应该显示一个 GUI，允许用户输入 SQL 查询，一旦单击执行按钮，结果集应在 GUI 上显示为表格。我可以看到空白表的初始轮廓，但是一旦执行查询，该表就不会更新。我对 Java GUI 很陌生，所以我可能会犯一个非常愚蠢的错误。我想也许我只是显示一个空白的不可编辑的滚动 Pane 而不是实际的表格，但我不再那么确定了。老实说，我不知道我哪里搞砸了。
我很确定清除按钮将与执行按钮类似，只是我需要创建一个空白表格，然后将其显示在那里。我只是无法让表格更新哈哈。无论如何，我要偏离主题了。我将粘贴下面的代码。下面粘贴了 2 个类。一个称为 QueryGUI，另一个称为 ResultTable。预先感谢您的帮助!
编辑:我可以做些什么来让这件事变得更容易帮助我吗？我已经盯着 Google、Oracle 网站和该网站上的其他线程看了几个小时，但我不知道为什么该表不会更新/显示。
EDIT2:弄清楚了，我试图将模型设置为我的滚动 Pane 而不是我的 JTable，这就是它不起作用的原因。
import java.sql.SQLException;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.EtchedBorder;
public class QueryGUI extends JFrame implements ActionListener{
private static ResultTable tableModel;
private static String[] jdbcDriverStrings = {"com.mysql.jdbc.Driver", "com.ibm.db2.jdbc.netDB2Driver",
"oracle.jdbc.driver.OracleDriver", "com.jdbc.odbc.jdbcOdbcDriver"};
private static String[] dbURLStrings = {"jdbc:mysql://localhost:3306/project4", "jdbc://localhost3306/bikedb",
"jdbc:mysql://localhost3306/test"};
static String JDBC_DRIVER = null;
static String DATABASE_URL = null;
static String USERNAME = null;
static String PASSWORD = null;
static String QUERY = null;
private static JComboBox driverList = new JComboBox(jdbcDriverStrings);
private static JComboBox dbURLList = new JComboBox(dbURLStrings);
private static JTextField usernameField = new JTextField(20);
private static JPasswordField passwordField = new JPasswordField(20);
private static JTable resultTable = new JTable(tableModel); // create JTable delegate for tableModel
private static JTextArea sqlCommandEntry = new JTextArea(7, 30);
private static JScrollPane scrollingSQLCommandEntry = new JScrollPane(
sqlCommandEntry, ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,
ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
private static JLabel connectionLabel = new JLabel("No Connection Now");
public static void addComponentsToPane(Container pane) {
JFrame frame = new JFrame("SQL Client GUI - (MJL)");
pane.setLayout(null);
//Create all the labels, combo boxes, buttons, and text fields/areas
JLabel comboAndTextLabel = new JLabel("Enter Database Information");
JLabel driverLabel = new JLabel("JDBC Driver");
JLabel dbURLLabel = new JLabel("Database URL");
JLabel usernameLabel = new JLabel("Username");
JLabel passwordLabel = new JLabel("Password");
JLabel SQLEntryLabel = new JLabel("Enter SQL Command");
JLabel SQLResultLabel = new JLabel("SQL Execution Result");
JButton connectButton = new JButton("Connect to Database");
JButton clearButton = new JButton("Clear Command");
JButton executeButton = new JButton("Execute SQL Command");
JButton clearResultButton = new JButton("Clear Result Window");
JScrollPane sqlResultArea = new JScrollPane(resultTable);
//scrollingSQLCommandEntry.setWrapStyleWord(true);
//scrollingSQLCommandEntry.setLineWrap(true);
pane.add(driverList);
pane.add(dbURLList);
pane.add(comboAndTextLabel);
pane.add(driverLabel);
pane.add(dbURLLabel);
pane.add(usernameLabel);
pane.add(passwordLabel);
pane.add(usernameField);
pane.add(passwordField);
pane.add(SQLEntryLabel);
pane.add(scrollingSQLCommandEntry);
pane.add(connectionLabel);
pane.add(connectButton);
pane.add(clearButton);
pane.add(executeButton);
pane.add(SQLResultLabel);
pane.add(sqlResultArea);
pane.add(clearResultButton);
//pane.add(new JScrollPane(resultTable), BorderLayout.CENTER);
driverList.addActionListener(driverList);
dbURLList.addActionListener(dbURLList);
Insets insets = pane.getInsets();
//The next giant block of code takes each component and moves them to the
//desired space on the GUI. It uses absolute positioning
//This section moves the 5 labels on the top left
Dimension size = comboAndTextLabel.getPreferredSize();
comboAndTextLabel.setBounds(8 + insets.left, 5 + insets.top,
size.width, size.height);
size = driverLabel.getPreferredSize();
driverLabel.setBounds(8 + insets.left, 26 + insets.top,
size.width, size.height);
size = dbURLLabel.getPreferredSize();
dbURLLabel.setBounds(8 + insets.left, 54 + insets.top,
size.width, size.height);
size = usernameLabel.getPreferredSize();
usernameLabel.setBounds(8 + insets.left, 80 + insets.top,
size.width, size.height);
size = passwordLabel.getPreferredSize();
passwordLabel.setBounds(8 + insets.left, 105 + insets.top,
size.width, size.height);
//This section moves the combo boxes and the text fields on the top left
size = driverList.getPreferredSize();
driverList.setBounds(90 + insets.left, 22 + insets.top,
size.width + 90, size.height);
size = dbURLList.getPreferredSize();
dbURLList.setBounds(90 + insets.left, 51 + insets.top,
size.width + 65, size.height);
size = usernameField.getPreferredSize();
usernameField.setBounds(90 + insets.left, 80 + insets.top,
size.width + 73, size.height);
size = passwordField.getPreferredSize();
passwordField.setBounds(90 + insets.left, 104 + insets.top,
size.width + 73, size.height);
//This section moves the label and text area on the top right
size = SQLEntryLabel.getPreferredSize();
SQLEntryLabel.setBounds(425 + insets.left, 5 + insets.top,
size.width, size.height);
size = scrollingSQLCommandEntry.getPreferredSize();
scrollingSQLCommandEntry.setBounds(425 + insets.left, 24 + insets.top,
size.width - 1, size.height + 4);
//Puts a border around the text area on the right
sqlCommandEntry.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.LOWERED));
//Moves the connection status label and 3 middle buttons, also sets label color to red
size = connectionLabel.getPreferredSize();
connectionLabel.setForeground(Color.RED);
connectionLabel.setBounds(8 + insets.left, 180 + insets.top,
size.width + 175, size.height);
size = connectButton.getPreferredSize();
connectButton.setBounds(297 + insets.left, 175 + insets.top,
size.width, size.height);
size = clearButton.getPreferredSize();
clearButton.setBounds(456 + insets.left, 175 + insets.top,
size.width, size.height);
size = executeButton.getPreferredSize();
executeButton.setBounds(588 + insets.left, 175 + insets.top,
size.width, size.height);
//Moves SQL execution label and text area as well as clear result window button
size = SQLResultLabel.getPreferredSize();
SQLResultLabel.setBounds(8 + insets.left, 200 + insets.top,
size.width, size.height);
size = sqlResultArea.getPreferredSize();
sqlResultArea.setBounds(8 + insets.left, 217 + insets.top,
size.width + 295, size.height - 177);
//puts border around result text area
resultTable.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.LOWERED));
size = clearResultButton.getPreferredSize();
clearResultButton.setBounds(20 + insets.left, 451 + insets.top,
size.width, size.height);
connectButton.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent event){
try {
char[] tempPass = null;
USERNAME = usernameField.getText();
tempPass = passwordField.getPassword();
PASSWORD = String.valueOf(tempPass);
JDBC_DRIVER = (String)QueryGUI.driverList.getSelectedItem();
DATABASE_URL = (String)QueryGUI.dbURLList.getSelectedItem();
tableModel = new ResultTable(JDBC_DRIVER, DATABASE_URL, USERNAME, PASSWORD);
connectionLabel.setText("Connected to " + DATABASE_URL);
}
catch(ClassNotFoundException classNotFound){
JOptionPane.showMessageDialog(null,
"MySQL driver not found", "Driver not found",
JOptionPane.ERROR_MESSAGE);
System.exit(1); // terminate application
}
catch(SQLException sqlException){
JOptionPane.showMessageDialog(null, sqlException.getMessage(),
"Database error", JOptionPane.ERROR_MESSAGE);
// ensure database connection is closed
tableModel.disconnectFromDatabase();
System.exit(1); // terminate application
}
}
}
);
//create event listener for executeButton
executeButton.addActionListener(
new ActionListener(){
// pass query to table model
public void actionPerformed(ActionEvent event){
// perform a new query
try{
tableModel.setQuery(sqlCommandEntry.getText());
//These next 2 lines don't work. Bottom one line throws an eror message window
//stating can't execute query
//tableModel = new ResultTable(JDBC_DRIVER, DATABASE_URL, USERNAME, PASSWORD);
//tableModel.setUpdate(sqlCommandEntry.getText());
}
catch(SQLException sqlException){
JOptionPane.showMessageDialog(null, sqlException.getMessage(),
"Database error", JOptionPane.ERROR_MESSAGE );
}
}
}
);
}
//JDBC Driver combo box action
public void actionPerformed(ActionEvent e){
if(e.getSource() == QueryGUI.driverList){
//JComboBox cb = (JComboBox)e.getSource();
JDBC_DRIVER = (String)QueryGUI.driverList.getSelectedItem();
}
if(e.getSource() == QueryGUI.dbURLList){
DATABASE_URL = (String)QueryGUI.dbURLList.getSelectedItem();
}
}
//Create the GUI and show it.
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("SQL Client GUI - (MJL)");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Set up the content pane.
addComponentsToPane(frame.getContentPane());
//Size and display the window.
Insets insets = frame.getInsets();
frame.setSize(785 + insets.left + insets.right,
525 + insets.top + insets.bottom);
frame.setVisible(true);
//dispose of window when user quits application (this overrides
// the default of HIDE_ON_CLOSE)
frame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
// ensure database connection is closed when user quits application
frame.addWindowListener(
new WindowAdapter(){
// disconnect from database and exit when window has closed
public void windowClosed(WindowEvent event){
tableModel.disconnectFromDatabase();
System.exit(0);
}
}
);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
//new QueryGUI();
createAndShowGUI();
}
});
}
}
这是第二节课
import java.sql.Connection;
import java.sql.Statement;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import javax.swing.table.AbstractTableModel;
public class ResultTable extends AbstractTableModel{
private Connection connection;
private Statement statement;
private ResultSet resultSet;
private ResultSetMetaData metaData;
private int numberOfRows;
// keep track of database connection status
private boolean connectedToDatabase = false;
// constructor initializes resultSet and obtains its meta data object;
// determines number of rows
public ResultTable(String driver, String url,
String username, String password)
throws SQLException, ClassNotFoundException{
// load database driver class
Class.forName(driver);
// connect to database
connection = DriverManager.getConnection(url, username, password);
// create Statement to query database
statement = connection.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
// update database connection status
connectedToDatabase = true;
// set query and execute it
//setQuery(query);
}
// get class that represents column type
public Class getColumnClass(int column) throws IllegalStateException{
// ensure database connection is available
if(!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
// determine Java class of column
try{
String className = metaData.getColumnClassName(column + 1);
// return Class object that represents className
return Class.forName(className);
}
catch(Exception exception){
exception.printStackTrace();
}
return Object.class; // if problems occur above, assume type Object
}
// get number of columns in ResultSet
public int getColumnCount() throws IllegalStateException{
// ensure database connection is available
System.out.println("inside getColumnCount");
if(!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
// determine number of columns
try{
return metaData.getColumnCount();
}
catch(SQLException sqlException){
sqlException.printStackTrace();
}
return 0; // if problems occur above, return 0 for number of columns
}
// get name of a particular column in ResultSet
public String getColumnName(int column) throws IllegalStateException{
// ensure database connection is available
if(!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
// determine column name
try{
return metaData.getColumnName(column + 1);
}
catch(SQLException sqlException){
sqlException.printStackTrace();
}
return ""; // if problems, return empty string for column name
}
// return number of rows in ResultSet
public int getRowCount() throws IllegalStateException{
// ensure database connection is available
if(!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
return numberOfRows;
}
// obtain value in particular row and column
public Object getValueAt(int row, int column) throws IllegalStateException{
// ensure database connection is available
if(!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
// obtain a value at specified ResultSet row and column
try{
resultSet.next(); /* fixes a bug in MySQL/Java with date format */
resultSet.absolute( row + 1 );
return resultSet.getObject( column + 1 );
}
catch(SQLException sqlException){
sqlException.printStackTrace();
}
return ""; // if problems, return empty string object
}
// set new database query string
public void setQuery(String query)
throws SQLException, IllegalStateException{
// ensure database connection is available
if(!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
// specify query and execute it
resultSet = statement.executeQuery(query);
// obtain meta data for ResultSet
metaData = resultSet.getMetaData();
// determine number of rows in ResultSet
resultSet.last(); // move to last row
numberOfRows = resultSet.getRow(); // get row number
// notify JTable that model has changed
fireTableStructureChanged();
}
// set new database update-query string - this isn't working presently.
//Gives me an error message saying "Cannot issue select".
/*public void setUpdate(String query)
throws SQLException, IllegalStateException{
int res;
// ensure database connection is available
if (!connectedToDatabase)
throw new IllegalStateException("Not Connected to Database");
// specify query and execute it
res = statement.executeUpdate(query);
// notify JTable that model has changed
fireTableStructureChanged();
} */
// close Statement and Connection
public void disconnectFromDatabase(){
if (!connectedToDatabase)
return;
// close Statement and Connection
try{
statement.close();
connection.close();
}
catch(SQLException sqlException){
sqlException.printStackTrace();
}
finally{ // update database connection status
connectedToDatabase = false;
}
}
}
最佳答案
这是一项伟大的努力。然而，您需要立即对大量代码进行故障排除。如果您想在将来尽快获得帮助，我建议您扔掉所有不必要的东西。例如，您可能会丢弃 GUI 中除 JTable 之外的所有组件。
最终，我相信您的问题是您正在静态创建 JTable。在您创建它时，您的 TableModel 尚未初始化，因此它被设置为 NULL。稍后，当您初始化 TableModel 时，它不会更新 JTable 的引用(它仍将设置为 null)。
我建议使用空构造函数创建 JTable，然后在构造 TableModel 后调用 setModel。
此外，如果您有可用的开发人员，我强烈建议您让一位经验丰富的开发人员对其进行审核(StackOverflow 并不是专门为此设计的)。虽然很明显您为此花费了大量精力，但这里有很多事情使代码难以阅读和维护，她可以帮助解释这些问题背后的原因。
例如:
- 您有很多静态变量，这往往会导致代码无法测试。
- 在 GUI 开发中往往不鼓励使用绝对定位。
- 您正在连接到数据库并在 Swing 事件线程中执行大量阻塞 I/O。
- 您的连接在应用程序的生命周期内保持 Activity 状态，这可能会消耗资源，通常您会希望使用连接池或使用短期连接。
关于java - JDBC，帮助在 Java GUI 中将结果集显示为表格，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19592178/