Desing pattern for designing a Java library

There is this design issue that I'm trying to figure out at work. Would appreciate some inputs.

We have a core C application that acts as an interface engine to facilitate multiple devices from talking to each other and exchanging messages in different formats. This application is installed on a server and a whole wide variety of devices can initiate communication with this server and exchange messages. Now we're trying to extend the scope of this application be providing a Web interface for a subset of operations - mostly monitoring the plethora of devices connected to the server.

The architecture that I have in mind is to write a Java library that can be used to talk to the core C application. Then create a REST API that makes calls to this Java library. This API will be accessed by the front-end application, further up the stack. I'm looking for suggestions on what design pattern to use for this library. The core task that it does is monitors a whole bunch of different devices that communicate with each other. Any help appreciated.