Ankit,
I assume that you get the data from the front end in a JSON structure which is having some fields with deep structures.As long as you get the data back to SAP in deep structures you can loop which ever the info you need and write it to a text file.
My query is why you want the data in text file and in which format ( ie how you shown the data in text file ) you intend to have it.This query is just for my info.
I work with JSON structures to and fro between front-end and SAP but never had a requirement to download the data to a text file so want to understand what is the actual requirement.
K.Kiran.