Question

I have a class with dependencies which I want to hot deploy without restarting the dependencies. The class has an interface but there’s only one concrete implementation.

Initially I created a single bundle with exported the interface and registered the implementation using activator and implementation classes which were not exported. However, if I update the bundle, bundles which use the registered service get restarted after the update when PackageAdmin#refreshPackages is called (this is automatic when using fileinstall).

I have fixed this by creating a separate api bundle.

Is this the best way to achieve this?

Would you ever have a bundle which exports its api and includes the implementation in the same bundle. As far as I can see any give bundle would either export all its classes or no classes. What am I missing?

Answer 1

It is definitely a best practice to separate API bundles from their implementations in OSGi. If you do this, then any bundle that uses the API only needs to import classes from the API bundle, which can allow you to change implementations at runtime without restarting your dependent bundles.

Ideally your implementation bundle would implement the interface and export implementation as a service on the API provided interface. This allows the client bundles to utilize the service without referencing the implementation bundle.