CompletionStageExample.java

package com.lightbend.akka.sample;

import akka.actor.AbstractActor;
import akka.actor.ActorSystem;
import akka.dispatch.OnSuccess;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.Executor;
import scala.compat.java8.FutureConverters;
import scala.concurrent.Future;
import static akka.dispatch.Futures.future;

public class CompletionStageExample extends AbstractActor {
    final ActorSystem system = ActorSystem.create("helloakka");

    @Override
    public Receive createReceive() {

      Future<List<String>> scalaFuture = future(new Callable<List<String>>() {
        public List<String> call() {
          return Arrays.asList("Hello", "World!");
            }
        }, system.dispatcher());

        final Executor ex = system.dispatcher();
        CompletionStage<List<String>> fromScalaFuture = FutureConverters.toJava(scalaFuture)
                .thenApplyAsync(s -> {
                    s.contains("Hello");
                    return s;
                }, ex)
                .thenApplyAsync(s -> {
                    s.contains("World");
                    return s;
                }, ex)
                .thenApplyAsync(s -> {
                    new PrintResult<List<String>>();
                    return s;
                }, ex);

        List<String> helloWorldStrings = fromScalaFuture.toCompletableFuture().join();
        return AbstractActor.emptyBehavior();
    }

    public final static class PrintResult<T> extends OnSuccess<T> {
        @Override public final void onSuccess(T t) {
            System.out.println(t);
        }
    }

}