Handling exceptions in SwingWorker

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Efi Merdler - 26 Feb 2007 16:37 GMT

Hello,
I didn't find any information on this subject.
Let's assume that I have an exception while running my background
method, what are my available options :
1. Handle the exception from within the background method, sometimes
not possible especially if it requires handling GUI.
2. Create a getter method called getException() that returns the
exception if one exists and null if none exists.
The background method can return some kind of a value indicating that
something wrong happened like null (although not always possible).
You have to make sure that the background methods terminates quietly
i.e. does not allow the exception to propagate up but to catch it.
In the done() method which is called after background method returned
you can check getException() and do what ever you think you should do
(logging, display an error message etc...)

Does the above solution sounds ok ?

Thanks,
Efi

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Michael Rauscher - 27 Feb 2007 05:17 GMT

> Hello,
> I didn't find any information on this subject.
[quoted text clipped - 4 lines]
> 2. Create a getter method called getException() that returns the
> exception if one exists and null if none exists.

OK, I'd like to add some possibilities:

3. Use a global 'ErrorManager'

4. Create an 'ExceptionListener' and a method addExceptionListener

5. Use a combination of 3 and 4

Bye
Michael

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Rogan Dawes - 27 Feb 2007 08:09 GMT

>> Hello,
>> I didn't find any information on this subject.
[quoted text clipped - 15 lines]
> Bye
> Michael

6. Extend SwingWorker to have both a done() and exception(Exception e)
method, both of which are called on the EDT. Depending on requirements,
you may want both methods to be called if an Exception occurs, or the
exception() method could chain to the done() method.

7. Catch the exception in your worker method, and set the return value
to the exception. In your done() method, check if you get an instance of
Exception and handle it appropriately.

Rogan

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Efi Merdler - 27 Feb 2007 19:23 GMT

> >> Hello,
> >> I didn't find any information on this subject.
[quoted text clipped - 26 lines]
>
> Rogan

Great !
How do you call a method on the EDT, do you use
SwingUtilities.InvokeLater(new Runner(...
exception(e));

?

Thanks,
Efi

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Rogan Dawes - 27 Feb 2007 21:05 GMT

>>>> Hello,
>>>> I didn't find any information on this subject.
[quoted text clipped - 34 lines]
> Thanks,
> Efi

I'd take a careful look at the source for SwingWorker. The concurrency
issues here are quite severe, it seems. It took 3 or more revisions of
SwingWorker by seasoned practitioners before it became robust . . .

Rogan

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Michael Rauscher - 28 Feb 2007 10:23 GMT

> How do you call a method on the EDT, do you use
> SwingUtilities.InvokeLater(new Runner(...
> exception(e));

SwingUtilities.invokeLater( new Runnable() {
public void run() {
exception(e);
}
});

You can also implement a method in non-EDT-safe way, too:

public void exception( final Throwable e ) {
if ( SwingUtilities.isEventDispatchThread() ) {
// manipulate the GUI
} else {
SwingUtilities.invokeLater( new Runnable() {
public void run() {
exception(e);
}
});
}
}

Bye
Michael

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Handling exceptions in SwingWorker

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