[FIXED] Best way to check whether a certain exception type was the cause (of a cause, etc ...) in a nested exception?

Issue

I am writing some JUnit tests that verify that an exception of type MyCustomException is thrown. However, this exception is wrapped in other exceptions a number of times, e.g. in an InvocationTargetException, which in turn is wrapped in a RuntimeException.

What's the best way to determine whether MyCustomException somehow caused the exception that I actually catch? I would like to do something like this (see underlined):

try {
    doSomethingPotentiallyExceptional();
    fail("Expected an exception.");
} catch (RuntimeException e) {
     if (!e.wasCausedBy(MyCustomException.class)
        fail("Expected a different kind of exception.");
}

I would like to avoid calling getCause() a few "layers" deep, and similar ugly work-arounds. Is there a nicer way?

Apparently, Spring has NestedRuntimeException.contains(Class), which does what I want - but I'm not using Spring.

Solution

Why would you want to avoid getCause. You can, of course, write yourself a method to perform the task, something like:

public static boolean isCause(
    Class<? extends Throwable> expected,
    Throwable exc
) {
   return expected.isInstance(exc) || (
       exc != null && isCause(expected, exc.getCause())
   );
}

Answered By - Tom Hawtin - tackline
Answer Checked By - Pedro (JavaFixing Volunteer)