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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: SAXException, checked, buy why?
* Karl Waclawek <karl@w...> [2005-01-03 12:21]:
> Alan Gutierrez wrote:
>
> >>> http://www.saxproject.org/apidoc/org/xml/sax/ErrorHandler.html
> > What if the type of error is not a SAXParseException? I'm
> > already feeling uncomfortable calling everything a SAXException.
> Yes, but that is the trouble with checked exceptions.
> Personally I think it would have been better to pass an object
> of some non-exception type to the error handler call-backs.
> The class could have been named SAXError, or SAXStatus.
> Actually, in SAX for .NET we have decided to pass a non-ecxeption
> class to the error handlers, but we are still calling it ParseError
> - so maybe we should rename it to SAXError, to be more generic.
Naming is important.
Thanks for this message. This is, for me, a very productive
discussion.
What you're saying, is that in .NET, you didn't bother with an
exception. This is in line with my thinking.
I'd like to treat the SAXError as a container and structure that
contains the necessary information to recover from the
exceptional situation. That it is also an Error, means that
there's a ready object for throwing, one with a correct strack
trace.
> Well - in our western society - what is not explicitly forbidden, is
> allowed. :-)
Sweet liberty.
> As an example for another possible approach, one could have
> defined all handlers to accept a "Status" object as additional
> parameter (based on some abstract class definition). Each handler
> in the chain could inspect and modify this object, allowing
> information to pass up and down. The application could register a
> concrete subclass instance of that Status class with the event
> generator, to provide for custom processing of errors.
I am working with a bevy resuable handlers that I reuse through
object composition. In any SAX content handler in a content
handler chain, I've got dozens of objects decorating and
delegating.
Its not one monolithic SAX content handler, but a composition of
SAX strategies.
I'd planned on using the event handler below, as described.
public interface SAXCassandra {
public void error(SAXError saxError);
}
The SAXError, although it will be an unchecked exception class,
will also provide context information.
It will be like the status object in your .NET API. There will
be an added benfit of being something that the error handler can
throw if things don't work out.
public class BarFooCassandara {
public void error(SAXError saxError) {
try {
throw error.getCause();
} catch (FileNotFoundException e) {
// Perhaps providing parse state is overexposure.
// I've wondered why FileNotFoundException didn't
// have a getFile() method since that would be what
// we need here.
String fileName = error.getElement() // (Not really SAX.)
.getAttributes()
.getValue("file-name");
if (!BarFileUtils.touch(new File(fileName))) {
// Throw SAXError since it's unchecked.
throw saxError;
}
// Otherwise, we are fine. Work with touched file.
} catch (FooResourceError e) {
if (!FooManager.freeUpSomeFoos()) {
// Wrap this in an exception type that the
// process initiator expects to catch.
throw new BarFooError(e);
}
} catch (Throwable e) {
// If the contianed exception is unchecked, throw
// that, otherwise, throw the saxError.
throw saxError.asUnchecked();
}
}
}
The SAXError class now looks like:
public final class SAXError extends Error {
public SAXError(Throwable cause) {
super("Error in SAX.", cause);
}
public Element getElement() { }
public Object getErrorObject() { } // This.
public Map getErrorInfo() { } // Even more Perlish.
}
The class in final because a SAX error is really just a wrapper
for a real, application error. No message either. That is found
in the real cause. Eh?
I've decided to forgo checked exceptions. (I've had my
awakening.) I'll have that debate with anyone, if they'd like,
so's to learn something. I know its a common an trollish debate,
so I've avoided it in the past. I will gladly read any
references on the state of that debate.
I am hoping I don't sound to confident, I'd still like to know
what's wrong with my thinking. There must be something.
Cheers.
--
Alan Gutierrez - alan@e...
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