RxJava2 and Retrofit 2.2.0 compatible factory, which wraps the {@link RxJava2CallAdapterFactory} and takes care of the error conversion.

RxErrorHandlingCallAdapterFactory.java

/**
 * RxJava2 and Retrofit 2.2.0 compatible factory,
 * which wraps the {@link RxJava2CallAdapterFactory} and takes care of the error conversion.
 *
 * Based on: https://github.com/square/retrofit/issues/1102#issuecomment-241250796
 */
public class RxErrorHandlingCallAdapterFactory extends CallAdapter.Factory {
    private final RxJava2CallAdapterFactory mOriginalCallAdapterFactory;

    private RxErrorHandlingCallAdapterFactory() {
        mOriginalCallAdapterFactory = RxJava2CallAdapterFactory.create();
    }

    public static CallAdapter.Factory create() {
        return new RxErrorHandlingCallAdapterFactory();
    }

    @Override
    public CallAdapter<?, ?> get(final Type returnType, final Annotation[] annotations, final Retrofit retrofit) {
        return new RxCallAdapterWrapper<>(retrofit, mOriginalCallAdapterFactory.get(returnType, annotations, retrofit));
    }

    private static class RxCallAdapterWrapper<R> implements CallAdapter<R, Observable<R>> {
        private final Retrofit mRetrofit;
        private final CallAdapter<R, ?> mWrappedCallAdapter;

        public RxCallAdapterWrapper(final Retrofit retrofit, final CallAdapter<R, ?> wrapped) {
            mRetrofit = retrofit;
            mWrappedCallAdapter = wrapped;
        }

        @Override
        public Type responseType() {
            return mWrappedCallAdapter.responseType();
        }

        @SuppressWarnings("unchecked")
        @Override
        public Observable<R> adapt(final Call<R> call) {
            return ((Observable) mWrappedCallAdapter.adapt(call)).onErrorResumeNext(new Function<Throwable, ObservableSource>() {
                @Override
                public Observable apply(final Throwable throwable) {
                    return Observable.error(asRetrofitException(throwable));
                }
            });
        }

        private RetrofitException asRetrofitException(final Throwable throwable) {
            // We had non-200 http error
            if (throwable instanceof HttpException) {
                final HttpException httpException = (HttpException) throwable;
                final Response response = httpException.response();

                return RetrofitException.httpError(response.raw().request().url().toString(), response, mRetrofit);
            }
            // A network error happened
            if (throwable instanceof IOException) {
                return RetrofitException.networkError((IOException) throwable);
            }

            // We don't know what happened. We need to simply convert to an unknown error

            return RetrofitException.unexpectedError(throwable);
        }
    }
}

@challme28 Look at this: http://bytes.babbel.com/en/articles/2016-03-16-retrofit2-rxjava-error-handling.html
And here is the original RetrofitException: https://gist.github.com/koesie10/bc6c62520401cc7c858f#file-retrofitexception-java

@marvinmosa
Look at this: https://gist.github.com/julianfalcionelli/a585d2cb2fbaca2e123ae7df3e36fa39

Did anyone had this Exception?
java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.reflect.Type retrofit2.CallAdapter.responseType()' on a null object reference
line 34.

Any ideas why mWrappedCallAdapter might be null?

@zkvarz

I have same issue now. Trying to find solution.

Have you solved that issue?

Same here! @zkvarz @arnoid

Have you solved that issue?