Java Optional orElseThrow with empty collection

Question

I\'m implementing a stream in which I use a collection listOfFoo to get ids of all items in that list and use them to get values of Bar instances.

Answer 1

Just add an Optional.filter for it then. You could do it as :

List bars = Optional.ofNullable(
        listOfFoos.stream().map(fooId -> service.getBars(fooId))
                .filter(Objects::nonNull).collect(Collectors.toList()))
        .filter(a -> !a.isEmpty())
        .orElseThrow(() -> new ResourceNotFoundException(Bar.class, OBJECT_NULL));

Aside: By the implementation shared in the code, the list returned by the stream could not be null, so Optional.ofNullable could possibly be replaced by Optional.of.