Which is the best way to create a stream out of a collection:
final Collection entities = someService.getArrayList();
The second one does not do what you think it does! It does not give you a stream with the elements of the collection; instead, it will give you a stream with a single element, which is the collection itself (not its elements).
If you need to have a stream containing the elements of the collection, then you must use entities.stream().