Johan, it seems that your point is then related to what I asked a couple of
months ago
https://www.mail-archive.com/users%40felix.apache.org/msg15540.html
Check the whole thread, it might be of use to you
-----Original Message-----
From: Johan Ström [mailto:[email protected]]
Sent: Friday, February 13, 2015 11:13 AM
To: [email protected]
Subject: Re: Some questions regarding iPOJO
On 13/02/15 16:54, Endo Alejandro wrote:
I am no iPojo expert so I might be raising more questions than I'm
answering
You said
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
I don’t think that's how instantiation works or, at least to me, you
seem to be mixing two different concepts. If you don't want that
initial instance then you need to just remove @Instantiate. Then, as
you say, the component does not become available, that's expected.
Then you have to instantiate the component using one of the techniques
discussed here
http://felix.apache.org/documentation/subprojects/apache-felix-ipojo/a
pache-felix-ipojo-userguide/apache-felix-ipojo-instances.html
You see the first one is @Instantiate, which doesn't work for you
since you don't want a single instance Just use one of the other
techniques, they are more imperative/less declarative than
@Instantiate
My question/surprise is that I didn't know you could use @Instantiate with strategy
"instance". I always saw @Instantiate more for singleton services. Is that
incorrect??
From what I've understood from the docs, @Instantiate would be for singletons
only. So, no it doesn't make much sense to use it here. I was just
experimenting with it, and for some reason it triggers *almost* the behavior I
was trying to get (i.e. create new instances for each dependent instance).
I suppose/hope there is a "correct" way to get that working, the question is
how? :) I've done some more experimentation, and I can manage to create my instances
dynamically, with my own properties, using the Factory.createComponentInstance pattern..
But that seems pretty messy to me. Especially when it at least seems to work like above
(although not with properties, hence my questions regarding propagation).
Johan
Alejandro
-----Original Message-----
From: Johan Ström [mailto:[email protected]]
Sent: Friday, February 13, 2015 10:19 AM
To: [email protected]
Subject: Some questions regarding iPOJO
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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