Hello all, We are developing a desktop application based on Felix and thinking about the best approach to support plugins and extension points. My goal at the moment is to try to use only OSGi configuration for this, that is without any additional plugin/extensions descriptors. Another important goal is to load lazily, i.e. extensions are loaded only when they are requested, not when bundle which uses them is loaded.
If you look at Eclipse they have plugins as OSGi bundles. A plugin could define its own extension points and provide extensions to the other extension points. The extension point mechanism Eclipse uses is NOT based on OSGi, that is they have a plugin descriptor in plugin.xml, eclipse framework code reads those descriptors at startup and keeps all the wiring between extension points and their extensions ready in memory. When an extension point requests all its extensions the framework will traverse the wiring and will load and activate the required plugins (if they have not been activated yet) and then it will create the extensions. Basically to create an extension in Eclipse one needs to provide an implementation (key1) and specify which extension point it extends (key2). Two keys here. If I want to use say declarative services (or simply services) as extension points mechanism it seems I have only one key: service interface, that is when I declare my service I just announce to the framework that I have a service, I don't specify which extension point this service is intended to extend. I guess I can add some parameter to the service (i.e. extension point name) and have the framework code filter out services by this parameter when requested. It could work, but I don't really like this approach because these parameters are somewhat soft constraints and not enforced by OSGi in any way. Another reason I don't like it is because I suspect that the service (extension) will be loaded when a component requesting this service is loaded, but I want it to be loaded only when I specifically requested this service. Anybody has any thoughts/ideas on that? Are we reinventing a wheel? Thanks! -- Dmitry Skavish
