Catching throwable and handling specific exceptions

Question

Ok I know catching throwable is not a good idea:

    try {          // Some code     } catch(Throwable e) { // Not cool!         // handle the exception     } 

But recently I was reading through an open sourced code and I saw this interesting (at least to me) piece of code:

    try {         // Some Code     } catch (Throwable ex){         response = handleException(ex, resource);     }      private handleException(Throwable t, String resource) {         if (t instanceof SQLEXception) {                // Some code         } else if (t instanceof IllegalArgumentException) {                //some code         } //so on and so forth     } 

This doesn't seem to be that bad? What is wrong with this approach?

Answer 1

There are various reasons why you should not catch a Throwable. First of all is, that Throwable includes Errors - and there's normally not much an application can do if one of these appears. Also Throwable reduces your chances of finding out, WHAT has happened. All you get is "something bad has happened" - which might be a catastrophe or just a nuisance.

The other aproach is better but of course I still would not catch Throwable, but try to catch more specific Exceptions, if possible at all. Otherwise you are catching everything and then try to sort out which kind of bad thing happened. Your example could be written as...

try {     ... } catch (SQLEXception ex){     response = ... ; } catch (IllegalArgumentException ex){     response = ...; } 

...which would reduce the amount of if ( ... instanceof ... ) blocks (which are only needed because the author first decided to catch everything in one big bucket). It something actually throws Throwable, then you don't have much choice, of course.