convert Optional to Stream

Question

I want to convert an Optional<T> to a Stream<T>:

• If the optional does hold a value, the stream contains that value.
• If the optional does not hold a value, the stream should be empty.

I came up with the following:

public static Stream<T> stream(Optional<T> optional) {
    return optional.map(Stream::of).orElseGet(Stream::empty);
}

Is there a shorter way?

Answer 1

Upgrade to Java 9, you have a method there: https://docs.oracle.com/javase/9/docs/api/java/util/Optional.html#stream--

public Stream<T> stream​()

If a value is present, returns a sequential Stream containing only that value, otherwise returns an empty Stream.

Since: 9

Answer 2

Optional.of(10).map(Stream::of).orElseGet(Stream::empty);

In Java9 the missing stream method has been added, so the code would have been written like so,

optional.stream()

Answer 3

Your code return Stream<Stream<T>>. Try change to this

public static <T> Stream<T> stream(Optional<T> optional) {
    return optional
            .map(t -> Stream.of(t))
            .orElseGet(Stream::empty);
}

Answer 4

The code you posted does not compile. Why did you use an additional Stream.of(...)? This works:

public static <T> Stream<T> stream(Optional<T> optional) {
    return optional.map(Stream::of).orElseGet(Stream::empty);
}