Map Java 8 streams to RxJava Observables.

README.md

Output

Greeting: Hey
Greeting: Hi
Greeting: Hello

[60, 61, 62, 63, 64, 65, 66, 67, 68, 69]
[70, 71, 72, 73, 74, 75, 76, 77, 78, 79]
[80, 81, 82, 83, 84, 85, 86, 87, 88, 89]
[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

RxStreams.java

import java.util.Iterator;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import rx.Observable;
import rx.Subscriber;

public class RxStreams<T> extends Observable<T> {
  public static <T> RxStreams<T> from(Stream<T> stream) {
    return new RxStreams<T>(new OnStreamSubscribe<T>(stream));
  }

  protected RxStreams(OnStreamSubscribe<T> func) {
    super(func);
  }

  protected static class OnStreamSubscribe<T> implements OnSubscribe<T> {
    private final Stream<T> stream;

    public OnStreamSubscribe(Stream<T> stream) {
      this.stream = stream;
    }

    @Override public void call(Subscriber<? super T> subscriber) {
      for (Iterator<T> i = stream.iterator(); i.hasNext(); ) {
        if (subscriber.isUnsubscribed()) {
          return;
        }
        subscriber.onNext(i.next());
      }
      subscriber.onCompleted();
    }
  }

  public static void main(String... args) {
    Observable<String> o1 = RxStreams.from(Stream.of("Hey", "Hi", "Hello"));
    o1.map(s -> "Greeting: " + s).subscribe(System.out::println);

    Observable<String> o2 = RxStreams.from(IntStream.range(0, 100).mapToObj(String::valueOf));
    o2.skip(60).buffer(10).subscribe(System.out::println);
  }
}

Hello Jake,
isn't it better to use this simpler version?

Stream stream = ...
Observable.from(() -> stream.iterator());

@nottmey: thanks very much, I had been looking for this a while now! I am a bit confused, though, which signature of Observable.from is used when invoked with a callable? I cannot seem to find it: http://reactivex.io/RxJava/javadoc/rx/Observable.html

that would be: http://reactivex.io/RxJava/javadoc/rx/Observable.html#from(java.lang.Iterable)

or more succinctly, you can use

Stream stream = ...
Observable.from(stream::iterator);

...and to go back the other way - I worked this out: (RxJava Observable-to-java.util.Stream)

http://www.cogmission.ai/2016/04/06/speed-blog-how-to-convert-an-rx-observable-to-a-java-util-stream/