Back in 2014 I decided to develop a music visualiser, and since I was mostly working with Java at the time my choice fell on this very language. Sadly, I couldn't find any decent tutorials or examples of music visualiser implementation in Java, so I decided to make one myself. Keep in mind, this project was made when I hardly had any experience with Java and, unfortunately, I did not make use of Maven during the development process.
Active Visualiser is a pretty basic music visualiser written in Java. It uses reasonably trivial techniques to analyse the audio and then produce some visualisation using OpenGL. You can find the source code and some documentation on its GitHub page. Check out the video below for a simple demo of the visualiser.