how to access servlet only via specific port?

Hi all,
I have an app with 2 servlets, I want each servlet to be accessible via a different port.
so I open HTTP on my web server, on port 80 and 18080, but now BOTH servlets are available via BOTH ports.
how can I make sure that servlet 1 is accessible only via port 80, and servlet2 is only accessible via port 18080?
tnx