Which Java Optionals Approach Is Best for Mapping Objects to Optional Objects and Retrieving First Non-Empty Result Via Stream::flatMap?

Java Optional Integration with Stream::flatMap

Java developers seeking a concise way to map a list of objects to Optional objects and retrieve the first non-empty result using Java 8's Stream API may encounter a challenge.

The intuitive approach of using things.stream().flatMap(this::resolve).findFirst() is not feasible because Optional lacks a stream() method. This has led to the exploration of alternative solutions:

Java 16

Java 16 introduced Stream.mapMulti, enabling the following concise solution:

<code class="java">Optional<Other> result =
  things.stream()
        .map(this::resolve)
        .<Other>mapMulti(Optional::ifPresent)
        .findFirst();</code>

Java 9

Java 9 introduced Optional.stream, allowing for this simpler solution:

<code class="java">Optional<Other> result =
  things.stream()
        .map(this::resolve)
        .flatMap(Optional::stream)
        .findFirst();</code>

Java 8

In Java 8, the following approach using a helper method can be employed:

<code class="java">Optional<Other> result =
  things.stream()
        .map(this::resolve)
        .flatMap(Optional::ofNullable)
        .findFirst();

// Helper method that converts Optional<T> to Stream<T>
private static <T> Stream<T> streamOptional(Optional<T> optional) {
  return optional.isPresent() ? Stream.of(optional.get()) : Stream.empty();
}</code>

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