Catch a generic exception in Java?

Question

We use JUnit 3 at work and there is no ExpectedException annotation. I wanted to add a utility to our code to wrap this:

 try {
     someCode();         


        

Answer 1

I understand the impulse to try to simplify your exception-test idiom, but seriously: don't. Every possible choice you'll come up with is a cure that's worse than the disease. Especially JUnit 4's @ExpectedException nonsense! It is a too-clever frameworky solution, requiring everyone to learn how it works, as opposed to a plain self-evident bit of regular Java code. Worse, it gives you no way to wrap only the part of your test that you expect to throw the exception, so if an earlier setup step throws that same exception, your test will pass even though your code is broken.

I could write a long diatribe about this here (I'm sorry for not having enough time to), as we've had a lengthy discussion of this issue among Java engineers here at Google, and the consensus was that none of these crazy solutions are worthwhile. Get used to try/catch, it's really not that bad.

Answer 2

Generics are not types. They are not templates. They are compile time type checks, in Java. Exception blocks catch on type. You can catch(Exception e) or even catch(Throwable e) and then cast as needed.

Answer 3

Catch clause with type parameter is not possible:
http://docs.oracle.com/javase/tutorial/java/generics/restrictions.html#cannotCatch

Answer 4

You can also use an IDE that supports live template ( like IntellJ IDEA for instance ) and assign a shortcut like ee -> [tab] that inserts the try/catch/ignore for your and let you type the correct one.

Answer 5

@FunctionalInterface
 public interface ThrowingConsumer<T, E extends Exception> {
      void accept(T t) throws E;
 }

public static <T, E extends Exception> Consumer<T> errConsumerWrapper(ThrowingConsumer<T, E> throwingConsumer,
                   Class<E> exceptionClass, 
                   Consumer<E> exceptionConsumer) {
            return i -> {
                try {
                    throwingConsumer.accept(i);
                } catch (Exception ex) {
                    try {
                        exceptionConsumer.accept(exceptionClass.cast(ex));
                    } catch (ClassCastException ccEx) {
                        throw new RuntimeException(ex);
                    }
                }
            };
        }

3. Usage example

   Stream.of("a").forEach(errConsumerWrapper(i -> Integer.parseInt(i), NumberFormatException.class, Throwable::printStackTrace));

Answer 6

Well, you could just catch Exception and rethrow if it's not an expected Exception. Though good coding practice usually dictates that the success path of code should not be defined by an Exception, so you might want to rethink your design.