NullPointerException
Using any application of size, it’s almost inevitable that you’ll be slapped in the face time and time again with a bevy of NullPointerExceptions.
It’s hard to come up with a reasonable explanation of why these exceptions are so prevalent and commonplace. In fact, I have yet to come across a single application server that has never barfed out an NPE at some point or another.
Granted, in most cases it is the fault of the user; providing less than stellar input. J2EE descriptors are rather easy to get wrong, for example. You’d think though that a company that is able to muster up the resources to build a J2EE stack would be able to expend the fairly minimal amount of extra effort it takes to assume that users will pass in bad info, and handle it in a civilised and sociable manner.
JBoss (sorry, couldn’t resist) is a good example of that incredibly half-assed piss-poor lackadaisical approach. Very often, you get an NPE deep inside of JBoss code. The NPE is often repeated 3-4 times, wrapped inside of 2 or 3 other NPE’s. Sometimes you’re lucky and you actually get a helpful message that subtly hints of a vague area to begin sniffing around. Sometimes it’s particularly cruel and reports the wrong component entirely as the culprit, thus leading you on a wild goose chase familiar to those poor bastards trying to find decent documentation for any open source stuff.
Sadly, this particular ailment isn’t restricted to JBoss. JRun will also barf out endless reams of NPE’s if you so much as sneeze in its general direction. They also are of the ‘lets nest exceptions, it’s very helpful to end users’ school of thought that Weblogic now belongs to as well. Luckily, both of these servers will tend to hide that one crucial line of information describing the error you need in that behemoth of a trace. So if you do read it carefully, you might actually see it.
It really isn’t a very hard concept. Always expect bad input. If it can be entered into your code, then someone somewhere will enter it. Null checks are trivial and buy you a lot of love if they report clearly and coherently what is null, and why that’s bad. Don’t nest it, don’t obscure it, fail fast and helpfully.
