Hi,
On 26 nov. 2013, at 16:00, Bengt Rodehav <[email protected]> wrote:
> I'm getting a bit closer regarding the interceptors. Still two problems for
> me:
>
> a) I still don't understand how to get hold of my intercepted instance from
> within my interceptor. I get a reference to a DependencyModel from which I
> can get a ComponentInstance. But how do I go from there to my ComponentA
> class. I need to access the property "extenders" in order for my
> interceptor to do its job.
>
It depends how how is managed the extender property, let’s imagine it’s a
@Property. In this case, from the Dependency Model, you can retrieve the
component instance. From the instance, you have access to the introspection
layer (getInstanceDescription()), which let you analyze the iPOJO container.
To be a bit more clear, let’s see some code:
//First retrieve the configuration handler description from the instance
container:
ConfigurationHandlerDescription description = (ConfigurationHandlerDescription)
model.getComponentInstance().getInstanceDescription().getHandlerDescription("org.apache.felix.ipojo.properties”);
// Find the extenders property
String extenders = description.getPropertyByName("extenders").getValue();
// You have your value !
> b) Also, when the property "extenders" is changed, I need to force the
> interceptor to recalculate the dependencies. How can I accomplish that?
It also depends on how this reconfiguration happen. Let’s say that the instance
is reconfigured from the configuration admin or iPOJO reconfiguration
abilities. In these case being notified is quite simple, as you can register a
ConfigurationListener on the ConfigurationHandlerDescription object:
description.addListener(new ConfigurationListener() {
public void configurationChanged(ComponentInstance instance,
Map<String, Object> configuration) {
// The extender property may have been modified
}
});
Don’t forget to unregister the listener when the interceptor is unplugged from
the instance.
>
> Getting deeper into iPojo than I've been before…
It’s just the beginning…. (contributions are welcome if you see some dark(er)
area)
>
> /Bengt
>
>
> 2013/11/26 Bengt Rodehav <[email protected]>
>
>> Thanks Clement!
>>
>>
>> 2013/11/26 Clement Escoffier <[email protected]>
>>
>>> Hi,
>>>
>>> On 25 nov. 2013, at 20:19, Bengt Rodehav <[email protected]> wrote:
>>>
>>>> Hello Clement and as always thanks for your detailed answer!
>>>>
>>>
>>> You’re welcome.
>>>
>>>> It does seem a bit complicated to "require" an interceptor. Perhaps an
>>>> easier way of doing this might be possible in the future.
>>>
>>> I think it would be a good addition. Thinking about it.
>>>
>>>> Anyway, I'm not
>>>> exactly sure that I understood what you meant. Just to clarify:
>>>>
>>>> My Component A (the component to be intercepted) has the following code:
>>>>
>>>> @Property(name = "extenders", mandatory = false)
>>>> private String[] mExtenderIds;
>>>>
>>>> @Requires(optional = true, id = "extenders")
>>>> private IExtender[] mExtenders;
>>>>
>>>> Do you mean that I should put a filter on the @Requires with
>>> id="extenders"
>>>> (the intercepted = true) so that it can only be satisfied if my
>>> interceptor
>>>> has added that property?
>>>
>>> Exactly.
>>>
>>>>
>>>> But how do I then handle the situation where my Component A does not
>>>> require any extenders? In that case I was planning on setting the
>>>> dependency to optional to make my instance valid without any extenders.
>>>>
>>>> Or, perhaps I could first set the @Requires to mandatory (with the
>>> filter):
>>>>
>>>> @Requires(optional = false, id = "extenders",
>>> filter="(intercepted=true)")
>>>> private IExtender[] mExtenders;
>>>>
>>>> Then, if my interceptor sees that the instance does not require any
>>>> extenders it can set the dependency to become optional. This way I both
>>>> require the interceptor (via the filter) and I ensure that the only way
>>> to
>>>> allow the instance to be valid without the dependency is if the
>>> interceptor
>>>> has explicitly set the dependency to optional.
>>>
>>> That would work. You can change the optionality status of the dependency
>>> from the dependency model you get in the interceptor.
>>>
>>> Regards,
>>>
>>> Clement
>>>
>>>>
>>>> /Bengt
>>>>
>>>>
>>>>
>>>>
>>>> 2013/11/25 Clement Escoffier <[email protected]>
>>>>
>>>>> Hi,
>>>>>
>>>>>
>>>>> On 25 nov. 2013, at 11:04, Bengt Rodehav <[email protected]> wrote:
>>>>>
>>>>>> I've started to investigate using iPojo interceptors. I'm using iPojo
>>>>>> version 1.11.0. I want to accomplish the following:
>>>>>>
>>>>>> Component A can be "extended" by specifying a list of (required)
>>>>>> "extenders" (actually their id's), like this:
>>>>>>
>>>>>> @Property(name = "extenders", mandatory = false)
>>>>>> private String[] mExtenderIds;
>>>>>>
>>>>>> @Requires(optional = true, id = "extenders")
>>>>>> private IExtender[] mExtenders;
>>>>>>
>>>>>>
>>>>>> The property is optional but if any extenderId's are listed then the
>>>>>> @Requires should require that IExtender's with the corresponding
>>>>> extenderId
>>>>>> is started.
>>>>>>
>>>>>> The IExtender interface contains the following method:
>>>>>>
>>>>>> public String getExtenderId();
>>>>>>
>>>>>> Thus, every extender has an extenderId and if that id is listed in a
>>>>>> components "extender" property then the corresponding service should
>>> be
>>>>>> required, otherwise not.
>>>>>>
>>>>>> My idea (actually Clement's idea from a previous conversation on this
>>>>>> list). is to use a RankingInterceptor that returns an empty array
>>> until
>>>>> all
>>>>>> required services are present.
>>>>>>
>>>>>> I think this is doable but in order for my RankingInterceptor to
>>> work, it
>>>>>> must have access to the component's "extenders" property. It would
>>> then
>>>>> go
>>>>>> through all the services implementing the IExtender interface and if
>>>>> there
>>>>>> are extenders corresponding to the required extenderId's it would
>>> return
>>>>>> all of those, otherwise it would return an empty list. Also, if a
>>> list of
>>>>>> extenderId's was specified, then the service dependency is set to
>>>>>> mandatory, otherwise to optional.
>>>>>>
>>>>>> My problem is how to gain access to the configuration property (the
>>>>>> "extenders" property) of my component from the interceptor. How can I
>>> do
>>>>>> this?
>>>>>
>>>>> When the interceptor is hooked to a dependency, it receives the
>>> dependency
>>>>> model object. From this object you can retrieve the component instance
>>> and
>>>>> get the introspection metadata.
>>>>>
>>>>>>
>>>>>> Another question I have is how to make sure that the interceptor is
>>>>> active.
>>>>>> If the interceptor is not active then my component could become
>>>>> erroneously
>>>>>> valid. Would it be feasible to have a mandatory dependency on the
>>>>>> interceptor?
>>>>>
>>>>> Unfortunately not, at least not easily. What you can do is a
>>> combination
>>>>> between a filter and two interceptors: the ranking interceptors as you
>>> did,
>>>>> and a tracking interceptor. Let me explain:
>>>>>
>>>>> Let’s imagine your consumer with your service dependency. Add a filter
>>>>> that will be resolved only if your interceptor is there, something
>>> like:
>>>>> (intercepted=true).
>>>>> Your interceptor implement both tracking and ranking interceptors. When
>>>>> the accept method is called on your interceptor, it can ‘transform’
>>> the
>>>>> original service reference to add the ‘intercepted’ property
>>>>> (ref.addProperty(“intercepted”, true);) This modified service reference
>>>>> matches your filter. Then, do your ranking policy are we discussed.
>>>>>
>>>>> This solution ensure that your dependency can only be resolved if your
>>>>> interceptor is there. Indeed without the interceptor, the filter does
>>> not
>>>>> match.
>>>>>
>>>>> Regards,
>>>>>
>>>>> Clement
>>>>>
>>>>>>
>>>>>> /Bengt
>>>>>
>>>>>
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>>>>>
>>>>>
>>>
>>>
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