How to set classpath from GUI

Hello,
I have created a library of java code to make complex tasks, and I would like to use other libraries from within this code, which are only available in .jar format. When I run my .class file from within the GUI of comsol, it seems to set the classpath to the directory of the file I am running. How can I set the classpath to also include the .jar files?
Thank you
Daniel