Handle empty response with retrofit and rxjava 2.x

Question

When using rxjava 1.x i used to return Observable<Void> to handle empty response from retrofit:

@POST( "login" )
Observable<Void> getToken( @Header( "Authorization" ) String authorization,
                                       @Header( "username" ) String username,
                                       @Header( "password" ) String password );

But since rxjava 2.x won't emit anything with Void is there any good practice to handle those empty responses?

Maksim Ostrovidov · Accepted Answer · 2017-06-27T23:55:41.530

46

Completable was designed for such cases. It available since RxJava 1.1.1. From the official docs:

Represents a deferred computation without any value but only indication for completion or exception. The class follows a similar event pattern as Reactive-Streams: onSubscribe (onError|onComplete)?

So just change your method's return type:

@POST("login")
Completable getToken(@Header("Authorization") String authorization,
                     @Header("username")      String username,
                     @Header("password")      String password);

And rewrite your subscriber, e.g.:

apiManager.getToken(auth, name, pass)
    ...
    .subscribe(() -> {
        //success
    }, exception -> {
        //error
    });

edited Jun 27 '17 at 23:55

answered Jan 10 '17 at 08:05

Maksim Ostrovidov

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1

This solution won't work if the response can be either empty for success or error with body – dephinera Jul 09 '20 at 14:24
Good solution for "fire and forget" requests. Thanks! – Bugdr0id Nov 17 '20 at 10:39

Leo DroidCoder · Answer 2 · 2020-07-10T09:58:58.983

7

Another solution is:

@POST("login")
Observable<Response<Void>> getToken(@Header("Authorization") String authorization,
                                    @Header("username") String username,
                                    @Header("password") String password);

Update: But I would rather use Completable

edited Jul 10 '20 at 09:58

answered Dec 08 '17 at 10:46

Leo DroidCoder

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NickJ · Answer 3 · 2020-06-23T00:11:57.673

So the accepted answer is only partially correct. Completable will work in some cases where one and only one emission is expected, however, Completable will only emit once, and will not emit after that. It is similar to Single (except we ignore the value being emitted). Observable, on the other hand, can emit multiple times. So if the source observable will emit multiple times, the answer, at least in RxJava2, is to emit something like Observable<Irrelevant> (where Irrelevant is a static enum/class), or better yet Observable<Kotlin.Unit>.

public class Source {
    private PublishSubject<Kotlin.Unit> heartbeatOperation;
...
    void getHeartbeats() {
         while(getHeartbeatFromSource() != null) {
             hearbeatOperation.accept(Unit.INSTANCE);
         }  
    }

    public Observable<Unit> heartbeats() {
         return hearbeatOperation.hide();
    }
...
}


public class SourceConsumer {
   @Inject Source source;
...
    void printHearbeats() {
         source.heartbeats()
         .subscribe(unused -> {
             System.out.println("Heartbeat received at " + DateTime.now());
         });
    }
}

score -1 · Answer 4 · answered Jan 10 '17 at 08:23

Did you try using Observable<Object> ?

This is from the official documentation of RxJava 2:

enum Irrelevant { INSTANCE; }

Observable<Object> source = Observable.create((ObservableEmitter<Object> emitter) -> {
   System.out.println("Side-effect 1");
   emitter.onNext(Irrelevant.INSTANCE);

   System.out.println("Side-effect 2");
   emitter.onNext(Irrelevant.INSTANCE);

   System.out.println("Side-effect 3");
   emitter.onNext(Irrelevant.INSTANCE);
});

source.subscribe(e -> { /* Ignored. */ }, Throwable::printStackTrace);

Handle empty response with retrofit and rxjava 2.x

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