JavaRx parallelism

Main.java

package it.r.rx;

import org.apache.commons.lang.RandomStringUtils;
import rx.Observable;
import rx.functions.Action1;
import rx.schedulers.Schedulers;

import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {

    public static void main(String[] args) {
        final List<String> result = Observable.from(new Integer[]{4, 5, 6, 6, 7, 3})
            .doOnNext(debug("Init"))
            .flatMap(i -> Observable.defer(() -> toRandomList(i)).subscribeOn(Schedulers.io()))
            .doOnNext(debug("defer"))
            .flatMap(Main::chooseString)
            .doOnNext(debug("chooseString"))
            .toList()
            .doOnNext(debug("list"))
            .toBlocking()
            .single();
        System.out.println("\nresult = " + result);
    }


    public static Observable<List<String>> toRandomList(Integer n) {
        debug("perform IO").call(n);
        try {
            Thread.sleep(new Random().nextInt(3000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        debug("IO done").call(n);
        final List<String> result = Stream.iterate(0, t -> t + 1)
            .map(i -> RandomStringUtils.randomAlphanumeric(n))
            .limit(n)
            .collect(Collectors.toList());
        return Observable.just(result);
    }

    public static Observable<String> chooseString(List<String> list) {
        if (Math.random() > .3) {
            return Observable.just(list.get(new Random().nextInt(list.size())));
        }
        else {
            return Observable.empty();
        }
    }

    public static <T> Action1<T> debug(String s) {
        return o -> System.out.println(o + " | " + s + " | " + Thread.currentThread().getName());
    }

}