Dear Spring people

I'm new to the forum, so if my question is in the wrong topic you can always replace it to somewhere else.

My question is the following.
I want to show my users who are logged in a specific stylesheet depending on a setting of the user. If the stylesheet does not exists, I want to show a default stylesheet.

I tried a lot of things but I can't seem to figure out how I can check this kind of information. Should I use a ResourceLoader or something in my controller?

I use thymeleaf to render my content.

Thanks in advance!