java.beans.EventHandler defeats AWT exception handling

Name: gm110360 Date: 07/11/2003


FULL PRODUCT VERSION :
java version "1.4.2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2-b28)
Java HotSpot(TM) Client VM (build 1.4.2-b28, mixed mode)

FULL OPERATING SYSTEM VERSION :
Microsoft Windows 2000 [Version 5.00.2195]

A DESCRIPTION OF THE PROBLEM :
java.beans.EventHandler.invoke() catches any exceptions and
dumps them to stdout. This defeats any application
exception handling (e.g. via the sun.awt.exception.handler
property).

EventHandler.invoke() implements
java.lang.reflect.InvocationHandler.invoke() which is
declared to throw Throwable, so EventHandler.invoke() could
just rethrow InvocationTargetException.getTargetException()
which would allow AWT (or any other caller) to handle it.

Another alternative would be to allow the application to
set a java.beans.ExceptionListener on the instance returned
by EventHandler.create. EventHandler.invoke could then
notify the listener of any exceptions that occur.

The current behavior makes EventHandler a black hole that
hides exceptions from the caller.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Run the attached ExceptionHandler app
2. Press the "Handled" button - it prints a message saying
the exception was handled - because this class is
registered as the sun.awt.exception.handler and the
exception propagated to the AWT event loop.
3. Press the "Unhandled" button - EventHandler dumps the
stack to stderr. The application was given no chance to
handle the exception.

EXPECTED VERSUS ACTUAL BEHAVIOR :
I would expect EventHandler.invoke to allow the exception
to propagate up to the AWT event loop which would then
handle it.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
This is the output from first pressing the "Handled" button and then
the "Unhandled" button:


caught and handled AWT exception java.lang.RuntimeException: handled
java.lang.RuntimeException: unhandled
at ExceptionHandler.handleButton(ExceptionHandler.java:32)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke
(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke
(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at java.beans.EventHandler.invoke(EventHandler.java:377)
at $Proxy0.actionPerformed(Unknown Source)
at javax.swing.AbstractButton.fireActionPerformed
(AbstractButton.java:1767)
at javax.swing.AbstractButton$ForwardActionEvents.actionPerformed
(AbstractButton.java:1820)
at javax.swing.DefaultButtonModel.fireActionPerformed
(DefaultButtonModel.java:419)
at javax.swing.DefaultButtonModel.setPressed
(DefaultButtonModel.java:257)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased
(BasicButtonListener.java:258)
at java.awt.Component.processMouseEvent(Component.java:5021)
at java.awt.Component.processEvent(Component.java:4818)
at java.awt.Container.processEvent(Container.java:1525)
at java.awt.Component.dispatchEventImpl(Component.java:3526)
at java.awt.Container.dispatchEventImpl(Container.java:1582)
at java.awt.Component.dispatchEvent(Component.java:3367)
at java.awt.LightweightDispatcher.retargetMouseEvent
(Container.java:3359)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3074)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3004)
at java.awt.Container.dispatchEventImpl(Container.java:1568)
at java.awt.Window.dispatchEventImpl(Window.java:1581)
at java.awt.Component.dispatchEvent(Component.java:3367)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:445)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy
(EventDispatchThread.java:191)
at java.awt.EventDispatchThread.pumpEventsForHierarchy
(EventDispatchThread.java:144)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:130)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:98)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.beans.*;

public class ExceptionHandler {
public static void main(String args[]) {
System.setProperty
("sun.awt.exception.handler", "ExceptionHandler");

JFrame frm = new JFrame();
frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JButton button1 = new JButton("Handled");
button1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
throw new RuntimeException("handled");
}
});

JButton button2 = new JButton("Unhandled");
button2.addActionListener((ActionListener)EventHandler.create
(ActionListener.class,
new ExceptionHandler(), "handleButton"));

frm.getContentPane().setLayout(new BorderLayout());
frm.getContentPane().add(button1, BorderLayout.NORTH);
frm.getContentPane().add(button2, BorderLayout.SOUTH);
frm.pack();
frm.setVisible(true);
}

public void handleButton() {
throw new RuntimeException("unhandled");
}

// Signature for sun.awt.exception.handler
public void handle(Throwable e) {
System.out.println("caught and handled AWT exception " + e);
}
}
---------- END SOURCE ----------
(Review ID: 158659)
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