RXJava2: correct pattern to chain retrofit requests

Question

I am relatively new to RXJava in general (really only started using it with RXJava2), and most documentation I can find tends to be RXJava1; I can usually translate between

Answer 1

I would suggest using flat map (And retrolambda if that is an option). Also you do not need to keep the return value (e.g Single<FirstResponse> first) if you are not doing anything with it.

retrofitService.getSomething()
    .flatMap(firstResponse -> retrofitService.getSecondResponse(firstResponse.id)
    .subscribeWith(new DisposableSingleObserver<SecondResponse>() {
         @Override
         public void onSuccess(final SecondResponse secondResponse) {
            // we're done with both!
         }

         @Override
          public void onError(final Throwable error) {
             // a request request Failed, 
          }                        
   });

This article helped me think through styles in how I structure RxJava in general. You want your chain to be a list of high level actions if possible so it can be read as a sequence of actions/transformations.

EDIT Without lambdas you can just use a Func1 for your flatMap. Does the same thing just a lot more boiler-plate code.

retrofitService.getSomething()
    .flatMap(new Func1<FirstResponse, Observable<SecondResponse> {
        public void Observable<SecondResponse> call(FirstResponse firstResponse) {
            return retrofitService.getSecondResponse(firstResponse.id)
        }
    })
    .subscribeWith(new DisposableSingleObserver<SecondResponse>() {
         @Override
         public void onSuccess(final SecondResponse secondResponse) {
            // we're done with both!
         }

         @Override
          public void onError(final Throwable error) {
             // a request request Failed, 
          }                        
   }); 

Answer 2

Does this not work for you?

retrofitService
.getSomething()
.flatMap(firstResponse -> retrofitService.getSecondResponse(firstResponse.id))
.doOnNext(secondResponse -> {/* both requests succeeded */})
/* do more stuff with the response, or just subscribe */