More on SAX Exceptions

[Rob Lugt <roblugt@elcel.com>]

Further to the recent thread about throwing exceptions from user code, I
would like to clarify exactly what a SAX Driver should do when it encounters
exceptions.

There are two places that an application may be told about an exception: on
return from the parse() function or via one of the ErrorHandler interfaces.
I'm looking for clarification about how the following situations should be
handled:-

1)  The SAX Driver encounters some kind of system exception, let's say it
gets an I/O error attempting to read the document entity.  Should this (a)
be thrown as a SAXException returned from parse() or (b) should it be
wrapped in a SAXParseException and handed over to
ErrorHandler::fatalError()?

2)  A handler method, let's assume EntityResolver::resolveEntity()
encounters an unrecoverable problem.  It traps an IOException.  It decides
to wrap this in a SAXException and throw it.  What should happen next?
Should this exception be (a) returned to the caller of parse() or (b) should
it be wrapped in a SAXParseException and reported to an ErrorHandler if one
exists?

3)  If you answered (b) to either of the above, then what do you think
should be done when ErrorHandler::warning() throws an Exception.  (a) return
it to parse() or (b) wrap the exception in a SAXParseException and call
ErrorHandler::fatalError().

4)  Finally, what about when ErrorHandler::fatalError() rethrows the
SAXParseException, as is the case with DefaultHandler?  This must obviously
be returned to parse() otherwise we'd be in a real pickle.

I believe the correct answer to all of the above is (a), throwing a
SAXException will cause the SAX Driver to terminate and return the thrown
exception to the caller of parse().  Without this behaviour how could the
application force a parse to cease prematurely?  It couldn't because the
ErrorHandler may deal with it and allow the parse to continue.

So, this brings me to my final question: should a SAX Driver ever call the
ErrorHandler with a real (i.e. unexpected) exception, or will these always
be returned to the caller of parse().

Regards
~Rob

--
Rob Lugt
ElCel Technology
http://www.elcel.com/