The ConfigurationAdmin compendium service in OSGi does support persisting properties. In fact it does so by default (the data ends up in the bundle cache, so you need to make sure you're not wiping that on every restart, which is bad practice anyway).
If you use the one from Apache Felix, you even get an option to:
- Reconfigure the location where the data is persisted.
- Provide your own storage back-end, if you want to use a database or something.
See: http://felix.apache.org/documentation/subprojects/apache-felix-config-admin.html