I am forced to learn writing web services for my Mobile App, is it common scenario?

Yup. Standalone apps are uncommon these days.

Quite typical nowadays. It's a good thing though. You learn and you can customize the web service to your app needs which you are the one who knows better. There's nothing like trying to debug a misbehaving app for hours only to find out that it was a poorly written web service that was causing the problem all along. And then trying to explain to the other dev why and how to fix it.

Also had to write a web service for my company's Android app. I used the Play Framework (now at 2.5) which has come a long way in the last few years and it wasn't too terrible.