Exception Catcher
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringWriter;
import java.net.URL;
import java.util.EventListener;
import java.util.EventObject;
import java.util.Vector;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class ExceptionCatcherTester {
public ExceptionCatcherTester() {
JFrame f = new JFrame("Exception Catcher Tester");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final JTextArea textArea = new JTextArea();
textArea.setEditable(false);
JButton button = new JButton("Alive");
ActionListener buttonListener = new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("I'm Alive");
}
};
button.addActionListener(buttonListener);
final JTextField textField = new JTextField();
ActionListener textFieldListener = new ActionListener() {
public void actionPerformed(final ActionEvent e) {
// Code to load URL contents in separate thread
Runnable r = new Runnable() {
public void run() {
textField.setEditable(false);
String urlString = e.getActionCommand();
try {
System.out.println("Loading " + urlString);
textArea.setText("");
URL url = new URL(urlString);
InputStream is = url.openStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
StringWriter sw = new StringWriter();
char buf[] = new char[1024];
int count;
while ((count = br.read(buf, 0, 1024)) != -1) {
sw.write(buf, 0, count);
}
System.out.println("Done Loading");
updateTextArea(textArea, sw.toString());
} catch (IOException e) {
throw new ThreadException(this, e);
} finally {
textField.setEditable(true);
}
}
};
ExceptionCatcherThread runner = new ExceptionCatcherThread(r);
// Listener in case of exception
ThreadListener threadListener = new ThreadListener() {
public void exceptionHappened(ThreadException e) {
Throwable t = e.getSourceException();
final String message = t.getClass().getName() + ": "
+ t.getMessage();
Runnable r = new Runnable() {
public void run() {
JOptionPane.showMessageDialog(null, message);
}
};
SwingUtilities.invokeLater(r);
}
};
runner.addThreadExceptionListener(threadListener);
runner.start();
}
};
textField.addActionListener(textFieldListener);
Container c = f.getContentPane();
c.add(textField, BorderLayout.NORTH);
JScrollPane pane = new JScrollPane(textArea);
c.add(pane, BorderLayout.CENTER);
c.add(button, BorderLayout.SOUTH);
f.setSize(300, 300);
f.show();
}
public void updateTextArea(final JTextArea ta, final String text) {
// Because file loading happening not blocking event thread
// We have to set text area in event thread
Runnable r = new Runnable() {
public void run() {
ta.setText(text);
ta.setCaretPosition(0);
}
};
SwingUtilities.invokeLater(r);
}
public static void main(String args[]) {
new ExceptionCatcherTester();
}
}
class ExceptionCatcherThread extends ThreadGroup {
private Runnable runnable;
private Thread runner;
private Vector listenerList = new Vector(3);
/* For autonumbering our group. */
private static int threadInitNumber;
private static synchronized int nextThreadNum() {
return threadInitNumber++;
}
public ExceptionCatcherThread(Runnable r) {
super("ExceptionCatcherThread-" + nextThreadNum());
runnable = r;
// Create thread in this group
runner = new Thread(this, runnable);
}
public void start() {
runner.start();
}
/* Listener registration methods */
public synchronized void addThreadExceptionListener(ThreadListener t) {
listenerList.add(t);
}
public synchronized void removeThreadExceptionListener(ThreadListener t) {
listenerList.remove(t);
}
public void uncaughtException(Thread source, Throwable t) {
fireExceptionHappened(t);
super.uncaughtException(source, t);
}
protected void fireExceptionHappened(Throwable t) {
ThreadException e = (t instanceof ThreadException) ? (ThreadException) t
: new ThreadException(runnable, t);
Vector l;
synchronized (this) {
l = (Vector) listenerList.clone();
}
for (int i = 0, n = listenerList.size(); i < n; i++) {
ThreadListener tl = (ThreadListener) l.get(i);
tl.exceptionHappened(e);
}
}
}
class ThreadException extends RuntimeException {
Runnable runnable;
Throwable exception;
public ThreadException(Runnable r, Throwable t) {
runnable = r;
exception = t;
}
public ThreadException(Runnable r, Throwable t, String message) {
super(message);
runnable = r;
exception = t;
}
public Runnable getRunnable() {
return runnable;
}
public Throwable getSourceException() {
return exception;
}
}
class ThreadExceptionEvent extends EventObject {
public ThreadExceptionEvent(ThreadException source) {
super(source);
}
public Runnable getRunnable() {
ThreadException source = (ThreadException) getSource();
return (Runnable) source.getRunnable();
}
}
interface ThreadListener extends EventListener {
public void exceptionHappened(ThreadException e);
}
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