Concatenate Optional Lists

Question

I have three Optional> which have to be combined and returned. I tried to use Optional.map() and flatmap() but was not successful.

Answer 1

Something like :

return Optional.of(Stream.of(entity1.orElse(new ArrayList<>()), entity2.orElse(new ArrayList<>()), entity3.orElse(new ArrayList<>()))
            .flatMap(List::stream)
            .collect(Collectors.toList()));

or rather more readable as :

return Optional.of(Stream.of(entity1, entity2, entity3)
        .filter(Optional::isPresent)
        .map(Optional::get)
        .flatMap(List::stream)
        .collect(Collectors.toList()));