OSGI: What is the best approach to wait for a declarative service component to start?

Question

I have the following problem:

1: An OSGI bundle A (equinox) is activated, and the activator parses an XML file
2: in the XML file, a declarative service is requested, which is present in another bundle (B)
3: bundle B is not activated yet, so the activator of bundle A needs to wait

I know how to approach this purely in DS, but the parsing needs to be carried out in the activator. Also I do not want to fool around with start levels and the likes. Ideally, I would want to be able to register the service provided by bundle B when needed.

Is there an elegant way to achieve this?

Thanks,

Kees

Answer 1

OSGi services are dynamic by nature and therefore you should never depend on the availability of a service. You need to use some kind of service tracking via a ServiceTracker or better, go for the pure DS solution which does all the hard work for you.

Since you indicate that you must parse the XML file, I guess you decided to use some kind of external configuration with services to use. I would suggest to re-consider this type of architecture. You need to write a lot of code while often the same goals can be reached by using a combination of the configuration admin and declarative services/blueprint.