public static void main(String[] args) throws InterruptedException {
         System.out.println("main.1");
         Flowable<Integer> obs = Flowable.just(1, 2);
         System.out.println("main.2");
         Flowable<String> obs2 =
                 obs
                         .doOnNext(i -> System.out.println("obs.1 : " + i))
                         .compose(compose())
                         .doOnNext(i -> System.out.println("obs.2 : " + i));
         System.out.println("main.3");
         obs2.subscribe(i -> System.out.println("obs.subscribe"));
         System.out.println("main.4");
     }
 
     private static FlowableTransformer<Integer, String> compose() {
         System.out.println("func compose.1");
         FlowableTransformer<Integer, String> transformer = obsInt ->
                 obsInt
                         .doOnNext(i -> System.out.println("compose.1 : " + i))
                         .map(i -> "s" + i)
                         .doOnNext(i -> System.out.println("compose.2 : " + i));
         System.out.println("func compose.2");
         return transformer;
     }