get all (derived) interfaces of a class

Question

Apache Commons Lang has method you need: ClassUtils.getAllInterfaces

Guava Solution:

final Set<TypeToken> tt = TypeToken.of(cls).getTypes().interfaces();

This is a much more powerful and cleaner reflection API than the ancient Apache stuff.

Don't forget, Spring Framework has many similar util classes like Apache Commons Lang. So there is: org.springframework.util.ClassUtils#getAllInterfaces