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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?
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Each OSGi bundle is a tightly coupled, dynamically loadable collection of classes, jars, and configuration files. Each OSGi bundle explicitly declares the packages they provide and the packages they require. By enforcing explicit declarations, the OSGi framework can provide a powerful component model.
OSGi facilitates creating and managing modular Java components (called bundles) that can be deployed in a container. As a developer, you use the OSGi specification and tools to create one or more bundles. OSGi defines the lifecycle for these bundles. It also hosts them and supports their interactions in a container.
The key difference with OSGi is that a JAR is now all private, adding metadata in the manifest makes it a bundle that can safely share with other bundles. OSGi makes sure violations are detected ahead of time. So, can a bundle be used in place of a jar in a JavaEE application? yes, it is a normal JAR.
OSGi is a Java framework for developing and deploying modular software programs and libraries. Each bundle is a tightly coupled, dynamically loadable collection of classes, jars, and configuration files that explicitly declare their external dependencies (if any).
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.
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