This post by Ruchika Goyal walks you through the use of OSGi services and OSGi's service registry. It includes an extensive hands-on example on how these OSGi concepts fit in the overall scheme of server side programming. Read Ruchika Goyal's post on 'Experimenting with OSGi on the Server Side ' http://blog.xebia.com/2008/10/16/experimenting-with-osgi-on-server-side/