Question

I just had a pretty painful troubleshooting experience in troubleshooting some code that looked like this:

try {    doSomeStuff()    doMore() } finally {    doSomeOtherStuff() } 

The problem was difficult to troubleshoot because doSomeStuff() threw an exception, which in turn caused doSomeOtherStuff() to also throw an exception. The second exception (thrown by the finally block) was thrown up to my code, but it did not have a handle on the first exception (thrown from doSomeStuff()), which was the real root-cause of the problem.

If the code had said this instead, the problem would have been readily apparent:

try {     doSomeStuff()     doMore() } catch (Exception e) {     log.error(e); } finally {    doSomeOtherStuff() } 

So, my question is this:

Is a finally block used without any catch block a well-known java anti-pattern? (It certainly seems to be a not-readily-apparent subclass of the obviously well-known anti-pattern ‘Don’t gobble exceptions!’)

Answer 1

In general, no, this is not an anti-pattern. The point of finally blocks is to make sure stuff gets cleaned up whether an exception is thrown or not. The whole point of exception handling is that, if you can’t deal with it, you let it bubble up to someone who can, through the relatively clean out-of-band signaling exception handling provides. If you need to make sure stuff gets cleaned up if an exception is thrown, but can’t properly handle the exception in the current scope, then this is exactly the correct thing to do. You just might want to be a little more careful about making sure your finally block doesn’t throw.