Retrofit will throw error for 401,402 type server response if we want to catch that in RxJava, Things to do for Retrofit RxJava Error Handling -> Check OperatorMapResponseToBodyOrError.java for error handling other classes are just to instanciate the Rxjava adapter on proejct level

ApiCallActivity.java

  if (throwable instanceof HttpException) {
                Response response = ((HttpException) throwable).response();
                RetrofitError commonResponse = null;
                if (response != null) {
                    Gson gson = new Gson();
                    try {
                        commonResponse = gson.fromJson(response.errorBody().string(), RetrofitError.class);
                        CommonUtilities.showAlertDialog(context, commonResponse.getMessage());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }

                }
                webApiResponseInterface.onError(commonResponse);
            }