How to replace my old Java code with Optionals (Functional programming)?

Question

How to replace the below code using Java 8 Optionals (Functional programming)?

ClassA classA = dbService.findByA(a);

if (classA == null) {
    classA = dbService.findByB(b);
}

if (classA == null) {
    throw new Exception();
}

return classA;

edit: Maybe if I will make findByA and findByB returning Optional will make my code cleaner using Functional programming?

Answer 1

return Optional.ofNullable(Optional.ofNullable(dbService.findByA(a))
    .orElseGet(() -> dbService.findByB(b)))
    .orElseThrow(() -> new Exception());

Or, Java 9, a bit nicer:

Optional.ofNullable(dbService.findByA(a))
    .or(() -> Optional.ofNullable(dbService.findByB(b)))
    .orElseThrow(() -> new Exception());

Answer 2

This would work

Optional.ofNullable(
    Optional.ofNullable(dbService.findByA(a))
            .orElseGet(() -> dbService.findByB(b))
).orElseThrow(Exception::new);

I don't think this is much nicer.