For some reason (historic that made sense at the time I am sure), the Pi4J project followed the WiringPi software for pin layout. To quote their site:
Pi4J (by default) uses an abstract pin numbering scheme to help insulate software from hardware changes.
Pi4J implements the same pin number scheme as the Wiring Pi project
The good news is that ...
I don't know what you was exactly looking for but RPiCameraViewer application (the video streaming part of course) can be condensed to 4-5 classes and one library. If you don't need transition effects like fading controls, camera listing and so on, the interesting code is just split between the following files: