Retrofit CallAdapter for Rx Errors.

RxErrorCallAdapterFactory.java

public class RxErrorCallAdapterFactory extends CallAdapter.Factory {
  
  @Override
  public CallAdapter<?> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
    Class<?> rawType = getRawType(returnType);
    String canonicalName = rawType.getCanonicalName();
    boolean isSingle = rawType == Single.class;
    boolean isCompletable = rawType == Completable.class;
    // Return type not a Rx type.
    if (rawType != Observable.class && !isSingle && !isCompletable) {
      return null;
    }

    CallAdapter delegate = retrofit.nextCallAdapter(this, returnType, annotations);

    if (isCompletable) {
      return new CallAdapter<Completable>() {
        @Override public Type responseType() {
          return delegate.responseType();
        }

        @Override public Completable adapt(Call call) {
          return ((Completable) delegate.adapt(call)).onErrorResumeNext(
              throwable -> Completable.error(convertToDomainSpecificException(throwable)));
        }
      };
    } else if (isSingle) {
      return new CallAdapter<Single<?>>() {
        @Override public Type responseType() {
          return delegate.responseType();
        }

        @Override public Single<?> adapt(Call call) {
          return ((Single<?>) delegate.adapt(call)).onErrorResumeNext(
              throwable -> Single.error(convertToDomainSpecificException(throwable)));
        }
      };
    } else {
      return new CallAdapter<Observable<?>>() {
        @Override public Type responseType() {
          return delegate.responseType();
        }

        @Override public Observable<?> adapt(Call call) {
          return ((Observable<?>) delegate.adapt(call)).onErrorResumeNext(
              throwable -> Observable.error(convertToDomainSpecificException(throwable)));
        }
      };
    }
  }

  private Throwable convertToDomainSpecificException(Throwable throwable) {
    if (throwable instanceof HttpException) {
      Response response = ((HttpException) throwable).response();
      return DomainException.create(response);
    }
    return throwable;
  }
}