rxJava.java

String[] getIds = new String[]{"id:0", "id:1", "id:2", "id:3"};
        rx.Observable.just(getIds)
                .flatMap(new Func1<String[], Observable<String>>() {
                    @Override
                    public Observable<String> call(String[] strings) {
                        //dla kazdego id odpytaj api
                        return Observable.from(strings);
                    }
                }).flatMap(new Func1<String, Observable<Integer>>() {
            @Override
            public Observable<Integer> call(String osoba) {
                //get na szczegóły osoby
                return Observable.just(osoba.length());
            }
        }, new Func2<String, Integer, Boolean>() {
            @Override
            public Boolean call(String osoba, Integer szczegoly) {
                //save to realm: osoba wraz z jej szczegółami
                return true;
            }
        }).subscribe(new Action1<Boolean>() {
            @Override
            public void call(Boolean aBoolean) {
                //onNext
            }
        }, new Action1<Throwable>() {
            @Override
            public void call(Throwable throwable) {
                //onError
            }
        });