A simple way in Jcreator is to add a bat file as external tool: configure->option->tools->new->program
than add a bat file like this:makeJar.bat
jar cf output.jar *
once you have done it, simply add this external tools to your toolbar:
right click on toolbar->customise
select categorie "Tools" drag first tools icon to your toolbar.
you may also use/customise this tools http://www.java-gaming.org/forums/index.php?topic=17584.0
to make exacly what you want as for example read filename from a txt file as requiered by your first post.