Here you write your own subclass of org.nanohttpd.NanoWebSocketServer to configure and to serve the websocket requests. A small standard echo example is included as org.nanohttpd.samples.echo.DebugWebSocketServer. You can use it as a starting point to implement your own services.
The included class org.nanohttpd.SimpleWebServer is intended to be used as a starting point for your own implementation but it also can be used as is. Starting the class as is will start a HTTP server on port 8080 and publishing the current directory.