I am currently working to add OSGi modularity to a project for the purpose of plugins. The basic idea is that users can develop their own plugins that can be added at runtime to the main application to extend or modify its functions and/or capabilities.
For example, the main application uses Restlets to define an HTTP API for the application. The user may wish to create a plugin to add an endpoint with a specific function. Or they may wish to create a new entity that is stored in the database with a specific purpose.
I understand that this is not a 'true' OSGi modular application implementation and after some research I managed to quite easily add OSGi capability to the existing project with embedded Felix. Along with felix.fileinstall the application watches a deploy folder and automatically installs and starts the jar bundles that are dropped into the deploy folder (stops and uninstalls when removed).
So the basic idea is implemented and work great. What I'm struggling to understand is how I define and publish the main applications API (that can be implemented by any plugin bundles). On the flip side I don't understand how bundle developers can gain access to that API info?
In order for a bundle developer to be able to utilise the API they would need some sort of SDK?
One approach would be to set the Constants.FRAMEWORK_BUNDLE_PARENT framework launch property to your application class loader and the Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA framework launch property to the list of packages that you want to expose to plugins. The plugins would then use Import-Package in their bundle manifest for your application's packages in the same way as any other package.