I have created a custom rest API to expose the items in openHAB, now I need a custom UI to play around with the API that I have created. Can I do this using paper UI?
I don’t think so. I think you will need to write your own UI. PaperUI is designed and implemented to work with the built in OH REST API. If you have implemented a separate API then PaperUI would know nothing about it.
Given that you can do almost everything using the existing REST API, what drove you to create a new one?
I wanted to get the items in openHAB in different JSON format to expose it to other applications, hence, ended up creating a custom REST API application in angularJS for it.