You need to include a manifest file  which looks something like this:

Manifest-Version: 1.0
Class-Path: lib/somelib.jar
Main-Class: com.anthonyeden.MainClass



(Note: There must be a line feed after the Main-Class header.)

This file must be called MANIFEST.MF in the META-INF directory of your
JAR. You can find  more information on this if you look for information
about executable JARs.