Exctract the Stream from an Optional<Stream>

Question

Suppose I have an Optional containing a Stream:

Optional<Stream<Integer>> optionalStream = Optional.of(Stream.of(1, 2, 3));

Now I need to extract the Stream itself. If the Optional is empty, you want to get an empty Stream.

I'm looking of is something like flatStream() that performs transformation in one step. How can I do this?

My current attempt:

Stream<Integer> stream = optionalStream.stream().flatMap(Function.identity());

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The Context of the Problem

In my real scenario, I have something like this, which gives me a Stream<Optional<Foo>>:

stream.findFirst().map(e -> e.getChildren())

Answer 1

I guess you could use the orElseGet() method:

optionalStream.orElseGet(()->Stream.empty())