Designing an application interface referencing to different APIs under one roof

I want to implement an interface (or Design) with which my application could accept inputs from different resources like Webservices (REST/Soap), File upload, Database and xyz in near future.

My application will accept the input -> Process it with Business logic or Core logic -> Return back in the same format (as it was accepted as request)

Are there better ways to redesign this kind of requirement? and How we could bring all these APIs (Webservice /File / Database) together?