Hi there
I have been trying to implement a use-case, but I seem to be running
into walls ;) (Disclaimer: I can see multiple ways to implement this,
but would like to re-use the dependency injection and lazy
instantiation of DS).
My aim is to create configured service objects in the way that is
normally achieved by using a DS factory component with
configuration-policy require.
The catch is that the implementation of the objects I want to
configure and register as a service is not under my control and is
instanciated via a builder obtained from a factory that is registered
as an OSGi-service. Sounds a bit complicated, maybe it's clearer in
code.
@Component(
service = Foo.class,
configurationPolicy = ConfigurationPolicy.REQUIRE
)
public class FooServiceFactory implements ServiceFactory<Foo> {
@Reference // provides FooBuilder instances that are pre-configured via OSGi
private FooBuilderFactory fooBuilderFactory;
@Override
public Foo getService() {
FooBuilder fooBuilder = fooBuilderFactory.builder();
applyConfiguration(fooBuilder);
return fooBuilder.build();
}
private void applyConfiguration(FooBuilder fooBuilder) {
// apply OSGi configuration to FooBuilder object
}
... // ungetService omitted for brevity
}
As far as I understand, this is not currently possible. The bnd tool
shouts at the mismatch between the "service" attribute (Foo.class) and
the ServiceFactory interface and refuses to generate the SCR XML. With
a manually crafted XML, Apache Felix SCR ends up throwing exceptions.
And most likely both implementations are correct, as I could not find
anything supporting my use-case in the spec.
Can anyone on this list please confirm that this is not (currently) possible?
I think this use-case is relatively generic. It has two preconditions:
- the implementation of the service object (e.g. Foo) is out of my
control and can therefore not be enhanced with OSGi-specifics
- in order to be able to create the service object, dependencies on
other services are required
Does this sound like a possible addition to the Declarative Services
specification?
Regards
Julian
PS: For those curious on how this could be implemented today. One way
to implement this is to register the ServiceFactory (lazily) by hand.
Provided Foo is not a final class, another way is to create a wrapper
for Foo that delegates all calls to a "real" Foo instance. The
FooWrapper implementation is then under my control and can be enhanced
with DS annotations etc.
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