wireless printing using a thermal printer for an Android mobile app

We've developed a mobile app for Android. It's a point of sale app. We wish to add the functionality of printing different receipts using a thermal printer and the invoices (A4 format) using a desktop LAN printer.
For the connectivity, we want the printing module to be able to connect to different printers (thermal and desktop) using Bluetooth, WiFi or USB.

there will be some UI to develop in order to add a new printer, configure or delete the old ones and to choose what printer to use.
We want that the printer module be delivered in a stand alone package (a jar file for example) that we can integrate to our project.