Fail fast finally clause in Java

Question

Is there a way to detect, from within the finally clause, that an exception is in the process of being thrown?

See the example below:

try {
    // code that may or may not throw an exception
} finally {
    SomeCleanupFunctionThatThrows();
    // if currently executing an exception, exit the program,
    // otherwise just let the exception thrown by the function
    // above propagate
}

or is ignoring one of the exceptions the only thing you can do?

In C++ it doesn't even let you ignore one of the exceptions and just calls terminate(). Most other languages use the same rules as java.

Answer 1

Set a flag variable, then check for it in the finally clause, like so:

boolean exceptionThrown = true;
try {
   mightThrowAnException();
   exceptionThrown = false;
} finally {
   if (exceptionThrown) {
      // Whatever you want to do
   }
}

Answer 2

If you find yourself doing this, then you might have a problem with your design. The idea of a "finally" block is that you want something done regardless of how the method exits. Seems to me like you don't need a finally block at all, and should just use the try-catch blocks:

try {
   doSomethingDangerous(); // can throw exception
   onSuccess();
} catch (Exception ex) {
   onFailure();
}

Answer 3

If a function throws and you want to catch the exception, you'll have to wrap the function in a try block, it's the safest way. So in your example:

try {
    // ...
} finally {
    try {
        SomeCleanupFunctionThatThrows();
    } catch(Throwable t) { //or catch whatever you want here
        // exception handling code, or just ignore it
    }
}