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Date: Mon, 11 Jan 2016 09:35:17 +0100
From: ben@petinou.fr
To: dev@karaf.apache.org
Subject: How to manage several service instances with declarative services?
Message-ID: <86ce97d48759d7f266072e86986f0cf3@petinou.fr>
User-Agent: Roundcube Webmail/1.1.3

Hi everyone!

I asked a question on stackoverflow regarding the use of Declarative 
Services in Karaf to manage multiple instances of a service, provided by 
different implementations of such a service.

The question is explained in details here:

http://stackoverflow.com/questions/34706041/how-to-manage-several-service-instances-in-declarative-services

I received and answer telling me that using the @reference annotation on 
the list storing the services would solve my problem. For this, I would 
need to use DS 1.3.

I thus asked on Karaf users mailing list what was the version of Felix 
SCR provided with Karaf 4.0.3 
(http://mail-archives.apache.org/mod_mbox/karaf-user/201601.mbox/%3C8dbfa59508d5769609e2c78c0210c7aa%40petinou.fr%3E) 
and was told it was Felix SCR 2.0.2, which supports DS 1.3. So far so 
good.

I was also kindly advised to ask this kind of questions here. So here I 
am :-)

Following the answer on stackoverflow, I tried to add the @reference 
annotation to my service list like this:

@Reference(service = FileReader.class)
private List<FileReader> availableServices = new ArrayList<>();

But it does not compile: FileReaderFactory.java:[37,5] annotation type 
not applicable to this kind of declaration

My project has a dependency on:

<dependency>
     <groupId>org.osgi</groupId>
     <artifactId>org.osgi.compendium</artifactId>
     <version>5.0.0</version>
     <scope>provided</scope>
</dependency>

which seems to be the latest version available.

I thus tried the "older way" by using explicit bind/unbind methods like 
this:

     @Reference(service = FileReader.class, unbind = "removeService")
     public void addService(final FileReader serviceToAdd) {
         System.out.println("FileReaderFactory.addService");
         availableServices.add(serviceToAdd);
         System.out.println(availableServices);
     }

     public void removeService(final FileReader serviceToRemove) {
         System.out.println("FileReaderFactory.removeService");
         availableServices.remove(serviceToRemove);
         System.out.println(availableServices);
     }

If I have two implementations available, say TxtFileReader and 
XmlFileReader, only the first one is added to the list. The status of 
the second service (using scr:detail command) is "null".

What am I missing?

Kind regards,

Ben