how to call customed class in SoapUI?

Hi All,
I would like to call a method which I declare in one customed class. but how to register this class and then to be called in script step? just like the sample class of soapui affiliated: Greet.

I can use it like this:

def greet = new Greet("Aaron",log)

is there anybody can show your suggestion and solution here?

Thanks,
Aaron