TrueStory.java

import java.util.*;
import java.util.concurrent.*;
import java.util.stream.*;

public class TrueStory {

    private static final int SLEEP = 1;

    private final int count = 10;
    private final ExecutorService service = Executors.newFixedThreadPool(count);
    private final long start = System.currentTimeMillis();

    public static void main(String[] args) throws Exception {
        final TrueStory trueStory = new TrueStory();
        final List<Integer> result = trueStory.process();
        System.out.println(trueStory.elapsedSeconds());
        trueStory.service.shutdown();
    }

    private List<Integer> process() {
        return IntStream.range(0, count)
                    .boxed()
                    .map(i -> service.submit(() -> doIt(i)))
                    .map(TrueStory::extractFuture)
                    .flatMap(TrueStory::stream)
                    .collect(Collectors.toList());
    }

    private Integer doIt(final int value) throws Exception {
        TimeUnit.SECONDS.sleep(SLEEP);
        return value;
    }

    static Optional<Integer> extractFuture(final Future<Integer> future) {
        try {
            return Optional.of(future.get());
        } catch (InterruptedException | ExecutionException e) {
            return Optional.empty();
        }
    }

    static <T> Stream<T> stream(final Optional<T> value) {
        return value.map(Stream::of).orElse(Stream.empty());
    }

    private int elapsedSeconds() {
        return (int)Math.floor((System.currentTimeMillis() - start) / 1_000);
    }

}