control instantiation of osgi declarative service

Question

I am looking for a simple way to control the instantiation of a declarative service.

What I want is something like a factory which is asked to return an instance of a component, but where I can control the instantiation.

Currently I just found the ComponentFactory where I just can call newInstance with a given dictionary. But what I really want, is something like this, assuming IComponent is the declarative service interface and MyComponent is the implementation class

public class MyComponentFactory implements ? {

   public IComponent newInstance() {
       return new MyComponent("firstParameter", "secondParameter");
   }
}

Is there something possible like this with declarative services, or do I need to use my own service registration in a bundle activation code?

Thanks in advance

Answer 1

DS does not provide for the level of instance creation indirection you are looking for. DS will always use the public no-args constructor and then call the specified activator method to complete the instance initialization.

Answer 2

One alternative for such service instantiation control is using a combination of DS and CM.

You must set configuration-policy="require" in the DS xml and use CM to create a configuration instance that will be used to pass a Dictionary containing all properties that you need (only types supported by DS of course) to the created service instance. You can even use a propertie file plus Felix File Install for that connfiguration.

If that is not enough you have another alternative that is to track for new created service and call a setup(args) method just after you have added a configuration using CM.