multiple api request using retrofit and rx java

Question

I am new to android and I have a scenario where I want to get get data from multiple api. Let suppose api_a, api_b, api_c,

Answer 1

There are at least 2 ways to achieve this -

1) Using RxJava Zip operator (for parallel requests)

Get all the observables

Observable observable1 = retrofit.getApi_a();
Observable observable2 = retrofit.getApi_b();
Observable observable3 = retrofit.getApi_c();

Zip the observables to get a final observable

Observable> result = 
Observable.zip(observable1.subscribeOn(Schedulers.io()), observable2.subscribeOn(Schedulers
            .io()), observable3.subscribeOn(Schedulers.io()), new Function3>() {
    @Override
    public List apply(ResponseType1 type1, ResponseType2 type2, ResponseType3 type3) {
        List list = new ArrayList();
        list.add(type1.data);
        list.add(type2.data);
        list.add(type3.data);
        return list;
    }
});

now subscribe on the resultant observable

result.observeOn(AndroidSchedulers.mainThread())
            .subscribeWith(new Observer>() {
                @Override
                public void onSubscribe(Disposable d) {

                }

                @Override
                public void onNext(List s) {
                    Log.d(TAG, "s is the list with all the data");
                }

                @Override
                public void onError(Throwable e) {
                    Log.e(TAG, e.getMessage());
                }

                @Override
                public void onComplete() {

                }
            });

2) Using RxJava flatMap() operator. (To request serially one after another)

This is simple chaining of requests

    List result = new ArrayList<>();
    Disposable disposable = retrofit.getApi_a()
            .subscribeOn(Schedulers.io())
            .flatMap((Function>) response1 -> {
                result.add(response1.data);
                return retrofit.getApi_b();
            })
            .flatMap((Function>) response2 -> {
                result.add(response2.data);
                return retrofit.getApi_c();
            })
            .map(response3 -> {
                result.add(response3.data);
                return response3;
            })
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeWith(new DisposableObserver() {

                @Override
                public void onNext(Response3 response3) {
                    Log.d(TAG, "result variable will have all the data");
                }

                @Override
                public void onError(Throwable e) {
                    Log.e(TAG, e.getMessage());
                }

                @Override
                public void onComplete() {

                }
            });