Server :: Associate A Tomcat Context To A Domain Name?

I've got a server that runs on Ubuntu Server 11.04 amd64.

I've installed Tomcat 6 and Apache 2 servers.

On Tomcat, I installed Liferay portal as a WAR. I can access to my portal with the following address : http://localhost:8080/lportal

I would like to associate a domain name to the "/lportal" context so that I could access my webapp with the "http://my.domain.com" URL. To make it short, I'd like to access the webapp on "http://localhost:8080/lportal" with "http://my.domain.com".