Question

In Java, is there an elegant way to detect if an exception occurred prior to running the finally block? When dealing with ‘close()’ statements, it’s common to need exception handling within the finally block. Ideally, we’d want to maintain both exceptions and propagate them up (as both of them may contain useful information). The only way I can think of to do this is to have a variable outside the try-catch-finally scope to save a reference to a thrown exception. Then propagate the ‘saved’ exception up with any that occur in the finally block.

Is there a more elegant way of doing this? Perhaps an API call that will reveal this?

Here’s some rough code of what I’m talking about:

Throwable t = null;  try {       stream.write(buffer);  } catch(IOException e) {     t = e;   //Need to save this exception for finally     throw e; } finally {        try {        stream.close();   //may throw exception    } catch(IOException e) {       //Is there something better than saving the exception from the exception block?       if(t!=null) {          //propagate the read exception as the 'cause'--not great, but you see what I mean.          throw new IOException('Could not close in finally block: ' + e.getMessage(),t);       } else {          throw e;  //just pass it up       }        }//end close } 

Obviously, there are a number of other similar kludges that might involve saving the exception as an member variable, returning it from a method, etc… but I’m looking for something a bit more elegant.

Maybe something like Thread.getPendingException() or something similar? For that matter, is there an elegant solution in other languages?

This question actually spawned from comments in another question that raised an interesting question.

Answer 1

Your idea about setting a variable outside the scope of the try/catch/finally is correct.

There cannot be more than one exception propagating at once.