Re: How to manage several service instances with declarative services?

[ben]

Thanks David,

I tried that by get an error on karaf startup:
cannot register Component org.osgi.service.component.ComponentException: 
Component FileReaderFactory validation failed: Field value type must not 
be set for unary field references.

My class looks like this:

@Component
public class FileReaderFactory implements ReaderManager {
    @Reference(service = FileReader.class)
    private List<FileReader> availableServices;

    @Override
    public Data readFile(Path filePath) throws IOException {
        for (FileReader reader : availableServices) {
            if (reader.isFormatSupported(filePath)) {
                return reader.readFile(filePath);
            }
        }
        return null;
    }

    @Override
    public boolean isFormatSupported(Path filePath) throws IOException {
        for (FileReader reader : availableServices) {
            if (reader.isFormatSupported(filePath)) {
                return true;
            }
        }
        return false;
    }
}

Le 11.01.2016 18:47, David Jencks a écrit :
Well, you need cmpn 6 for the ds 1.3 annotations (in particular
@Reference applicable to a field).  I thought this was on maven
central but haven’t looked.  If necessary you can get it from the OSGI
site.

david jencks

On Jan 11, 2016, at 12:35 AM, b...@petinou.fr wrote:

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