genericexample.java

    public static <T,U> Observable<Response<T>> createRequest(U data, Func1<U, Call<T>> endpoint){
        return Observable.create(new Observable.OnSubscribe<Response<T>>() {
            @Override
            public void call(Subscriber<? super Response<T>> subscriber) {
                if (isThereInternetConnection()) {
                    Call<T> request = endpoint.call(data);
                    try {
                        Response<T> response = request.execute();
                        int code = response.code();
                        if (response.isSuccess()) {
                            subscriber.onNext(response);
                            subscriber.onCompleted();
                        } else if (code >= 400 && code < 500) {
                            subscriber.onError(new BadRequestException(response.errorBody()
                                    .string()));
                        } else {
                            subscriber.onError(new NetworkConnectionException());
                        }
                    } catch (Exception e) {
                        subscriber.onError(new NetworkConnectionException());
                    }
                } else {
                    subscriber.onError(new NetworkConnectionException());
                }
            }
        });
    }