A link I found:
Istead of doing it in Java, you could also find a command line program that provides this information and execute that program and get its output from Processing. For example https://medium.com/@george.seif94/the-4-best-command-line-tools-for-monitoring-your-cpu-ram-and-gpu-usage-692e3053000f shows a program called nvidia-smi that gives a lot of data. I just tried intel_gpu_top mentioned at https://awesomedetect.com/how-to-monitor-intel-integrated-gpu-usage-in-linux/ .