service binding to wrong interface

I am working on a server running debian with 2 nics, one goes to the
internet the other goes to the internal lan. This machine has a
iptables firewall with masquerading running. Services like apache and
tomcat work fine on it.
I am a programmer trying to start a java service that works on a
specific port i am using a random one like 8100. I have had a hole in
the iptables firewall specifically opened for this port. I am 100%
positive the port is not blocked. But the problem is the service is
only accesable from my internal lan. I believe when i start this
simple program it is binding itself to the internal lan interface and
so it only listens from that side. How can i get it to bind to the
external interface?

This is not a traditional service just a little program that listens on
a socket so i can't quite figure out how you do this on linux.

thanks a bunch...