Is it possible to filter out empty Optionals and map over the present ones in a single line with Java streams?

Question

I often find myself writing code like this:

return collectionOfOptionals.stream()
    .filter(Optional::isPresent)
    .map(Optional::get)
    .collect(toList());

But is there a way to compress those middle two lines into a single operation?

I can do this, but it feels even less satisfactory:

return collectionOfOptionals.stream()
    .flatMap(o -> o.map(Stream::of).orElseGet(Stream::empty))
    .collect(toList());

score 2 · Accepted Answer · answered Aug 14 '17 at 17:52

2

It seems that this is possible in Java 9, based on this question.

return collectionOfOptionals.stream()
    .flatMap(Optional::stream)
    .collect(toList());

This is much nicer. But what I have already will have to do in Java 8.

answered Aug 14 '17 at 17:52

Peter Hall

Even the `flatMap` is unnecessary, it is called a `flatten` operation that Java doesn't have. Java 8 half-a$$ed `Optional` can't be converted to a `Stream`, so... – Abhijit Sarkar Aug 15 '17 at 01:29

1 Answers1