System packages and Extender packages in OSGi

The OSGi spec allows the Framework (through its system bundle) to export the relevant packages from its parent classloader as system packages using the org.osgi.framework.system.packages property.As repacking the hosting JDK as a bundle isn't a viable option, one can use this setting to have the system bundle (or the bundle with id 0) export these packages itself.


Extension Bundles :Another possible option is to enhance the system bundle through extension bundles. These act as fragments;they are not bundles of their own but rather are attached to a host. Once attached, the fragment content (including any permitted headers) is treated as part of the host. Extension bundles are a special kind of fragments that get attached only to the Systembundle in order to deliver optional parts of the Framework (such as the Start Level service).


The System package entry is added using org.osgi.framework.system.packages = \ i
n java6-server.profile in the lib directory of the dm server


In both the above cases the classes are loaded by the bootclassloader and not a seperate bundle classloader.Hence these are candidates when we are considering putting classes at the boot class path.

ref:http://blog.springsource.com/2009/01/19/exposing-the-boot-classpath-in-osgi/.