Hello Arjun,
On Sep 18, 2008, at 12:57 , Arjun Panday wrote:
I've been playing with DependencyManager recently and I must say i
find the design and syntax extremely elegant and also much more
traceable than the SCR.
Thanks. :)
So much so that I was about to remove all my DeclarativeService XMLs
to replace them with a few lines of DependencyManager when i bumped
into an issue: I sometimes have a dependency on a class (as opposed
to an interface), but this is made impossible in DependencyManager
because of the use of proxies.
Here's a typical error i get when i try to bind a specific
classloader:
java.lang.IllegalArgumentException: java.lang.ClassLoader is not an
interface
at java.lang.reflect.Proxy.getProxyClass(Proxy.java:362)
at java.lang.reflect.Proxy.newProxyInstance(Proxy.java:581)
at
org
.apache
.felix
.dependencymanager
.ServiceDependency.getNullObject(ServiceDependency.java:96)
But i guess it would be the same if i was to bind any implementation
of an abstract class.
Yes it would. If a service is not available, the dependency manager
will use the Null Object Pattern to inject an object that "does
nothing". The ServiceDependency.getNullObject() is implemented using
dynamic proxies, which only work on interfaces.
I'd be quite sad to have to abandon DependencyManager for this
reason.. Does anyone know of a workaround, or a future release that
would address this issue?
For now, you might be able to work around this issue. For one, these
null objects will only be injected if you have optional dependencies
and you use automatic injection for them. So if you can avoid that
combination, that would help.
You can turn off injection for a ServiceDependency by configuring it
with setAutoConfig(false) and still get notifications using callbacks.
Up to now I have not had anybody use it with services that are not
interfaces, but I would not mind adding support for that. Obviously in
that case I cannot support that null object pattern "automatically"
anymore (automatically meaning me creating a proxy that does nothing)
but I could:
a) let the user supply some kind of factory method to supply a proxy
b) add an option to completely turn off the creation of null objects
c) anything reasonably that's suggested here :)
Greetings, Marcel
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