The simple answer is yes.How can it be achieved is a much more challenging question.Sincere there are so many parts to SAP, you'll have to consider what component of SAP you are looking to integrate to, and what types of integration that component supports, REST API is hopefully the answer, else you would have to try to directly connect to the supporting underlying Database.
If you have a SAP system which does not have a REST api, then the SAP Java Connector is your friend.
From within it you can call Function Modules, depending on your needs.
From my limited experience, exactly as Pai said, there can't be a general TW SAP connector, simply because there is no general operation that you must perform against a SAP. Every service that you will expose in a SAP Extension will be a service dedicated to your own business logic.
The logic of developing with the SAP Java Connector is something like:
1. Understand what you need to do in the SAP
2. Choose the corresponding FM that can do that (test via SE37 in the SAP Client)
3. Use that FM in the Extension, via a Service.
Most of the time I spent looking for Function Modules...
Hope it helps,