Exception vs. redirecting to an errorpage

Question

When should I throw an exception to the server and when shold I redirect the user to an error page?
Is there a clear distinction for when to use either of them?
/Niklas Andersson
Sweden

Answer 1

I seem to recall seeing an ad on TV about the upcoming (made for TV?) movie "Helen of Troy," over which a mythical war was fought. I dare say I'd rather fight to a bloody death for (fill in whatever your imagination wants) with Helen (or at least the actress playing her role) than face the religious conflict this Easter Sunday that answering such questions often engenders.
That said, my personal opinion is that you should throw exceptions, rather than redirect.
If you are using JSPs, the errorPage directive will dispatch (rather than redirect) to an error page JSP, conveniently filling in the variable 'exception' with whatever Exception you threw. At that point, you can display some sanitized message to a user, log the event to stderr (with a stack trace), use the JavaMail API to page your cell phone at 3 a.m. to alert you to the impending disaster on your site, etc. etc. etc. When I'm debugging, I even print the stack trace in an HTML comment block on the error page, so I can easily see what happened, without corrupting the "user friendly" graphics, blandly denying to our users that NullPointerExceptions are anything but planned routine maintenance, for which we sincerely apolgize.
When you redirect, you lose all this, and you lose the exception itself, so you have no clue what went wrong, unless you include code in each and every catch block in your entire system, to write the trace to some kind of log. The one you skip will invariably, it seems, be the place where the most exceptions end up getting caught.
Okay, now I'll let some zealot with an opposing point of view weigh in, after which you'll be right back where you started.
Cheers!
Jerry Oberle
perl -e 'printf "mailto%cg%s%cearthlink%cnet\n", 58, "oberle", 64, 46;'