Becoming Concise with Java 8's Optional and Stream::flatMap

When working with Java 8 streams, transforming a List to Optional and extracting the first Other value efficiently can be a challenge. While flatMap typically requires a return stream, the absence of stream() for Optional complicates matters.

Java 16 Solution

Java 16 introduces Stream.mapMulti, enabling a more concise approach:

Optional result = things.stream()
    .map(this::resolve)
    .mapMulti(Optional::ifPresent)
    .findFirst();

Java 9 Solution

JDK 9 adds Optional.stream, simplifying the task:

Optional result = things.stream()
    .map(this::resolve)
    .flatMap(Optional::stream)
    .findFirst();

Java 8 Solution

In Java 8, the following approach can be taken:

Optional result = things.stream()
    .map(this::resolve)
    .flatMap(o -> o.isPresent() ? Stream.of(o.get()) : Stream.empty())
    .findFirst();

Using a helper function to convert Optional to Stream:

static  Stream streamopt(Optional opt) {
    if (opt.isPresent())
        return Stream.of(opt.get());
    else
        return Stream.empty();
}

Optional result = things.stream()
    .flatMap(t -> streamopt(resolve(t)))
    .findFirst();