Hi,
I'm a new user in iPOJO land. Having used declarative services before, I
must say its quite nice!
I have a few questions which I have not been able to find any answers to:
a) What's the status on iPOJO 2.0? Last message I can find was from 2013.
My main interest for 2.0 is the support for inherited annotations, which
brings me to my second question.
b) Since annotation inheritance is not possible in iPOJO 1.x, I cannot
have a "base class" with @Updated, @Validated etc.
Are there any good design patterns which allows me do have as simple
implementation classes as possible?
What I'm after is something like this:
@Component(managedservice = "my.pid", immediate = true)
public class MyComponent extends MyBaseComponent {
@Override
protected void addResources(...) {
....
}
}
public abstract class MyBaseComponent {
@Validate
public void validate() {
// start up some magic server and configure it with default
stuff, lots of code which I dont want to repeat
// in every "real" component
addResources(...);
// done!
}
@Invalidate
public void invalidate() {
// teardown...
}
}
The base component does lots of stuff which is shared among components,
triggered on @Validate/@Invalidate.
The subclass (which there will be several implementations of) just does
the specifics for that particular component, but since
it inherits form the base class it will automatically get calls to
validate etc.
I realize this is not possible today due to the use of compile-time-only
annotations et all, and if the base component would be in compiled form,
the manipulator has no way of seeing those annotations.
I could just implement the methods in every class and call
super.<method>() but if possible, I'd like to avoid that.
Any suggestions?
c) Concerning the component instance lifecycle, more specifically
the call order of Validate/Invalidate/Updated.
On startup, it seems Updated is called, then Validate, then Updated
again (but not in all cases? Think I saw other order once..).
I see two approaches:
1) Ignore first Updated if validate has not yet been called. Start my
stuff in Validate. Reconfigure my stuff in Updated. Downside is that i
reconfigure it once directly after startup, which I'd like to avoid.
2) Ignore Updated unless Validate has been called. In Validate, just
mark "valid". In following Updated, reconfigure/startup as necessary.
Version 2 is what I'll go for I guess, but I wonder, is there any way to
detect if my component is valid or invalid, besides implementing
Validate/Invalidate which would just update a boolean?
d) Final question: I'm trying to wrap my head around services and
property propagation..
I've been playing with Provides/Requires, and Provides strategy
"instance". As long as I have @Instantiate on my service impl, it will
create
one instance at startup, and then one new for every iPOJO object which
requests the service, as expected. However, I'd like to avoid creating
that extra
instance on startup, but without @Instantiate, the component does not
become available at all and my depending components will stay invalid.
When it comes to property propagation, I cannot really find any examples
which makes us of this or any description
on how this actually is supposed to work. My made up idea of how it
could work is something like this:
Service component ZServerImpl provides ZServer interface, with
strategy=instance. It requires property "listenPort" to start.
Component Y, which Requires an ZServer instance.
Y is instantiated via config admin, and the config has property
"listenPort = 1234".
When ZServer var is accessed (or when Y is instantiated), the property
"listenport" is propagated down to XServerImpl when it is instantiated
solely for my Y instance.
Basically, a way to reuse the ZServerImpl service, separately
instantiated for each user, with params inherited from each config.
Is this at all how property propagation is supposed to work? If not, any
other patterns to archieve this?
Thanks for your efforts on iPojo (and all other Felix projects), and for
replies to these lengthy questions :)
Regards
Johan
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