How to track how long a windows process has been running for and create a log file.

Hi I've been lurking these forums for a while now and finally decided to create an account because this community has always had answers to all my programming questions.
Today I have a question that I can't seem to find an answer anywhere so if you guys could help that would be great.

I've been learning java programming for a while now and I have a small project in which I need to track when a certain program is opened and track for how long its used until its closed.
This needs to be a constant process that runs in the background and the logs must be kept for future reference.
I am not quite sure how to approach this or if it is even possible In JAVA to do such a thing if you guys could give me suggestions or examples on how to do this it would be really helpful.

Thanks in advance