I've written a book about this topic which is both available as ebook and paper book on my blog. Based on this I also wrote an article for Oracle Java Magazine to get you started quickly with Java on Raspberry Pi.

The inexpensive single-board computer works great with Java, making hardware development as easy as traditional software development.

Read the full article with link to source code, video etc. on blogs.oracle.com/javamagazine/getting-started-with-javafx-on-raspberry-pi