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From David Jencks <david_jen...@yahoo.com>
Subject Re: declarative Services
Date Sat, 01 Jun 2013 05:26:45 GMT

On May 31, 2013, at 3:10 PM, bokie <jms.cercas@gmail.com> wrote:

> I'm quite comfortable with OSGi and Felix but have I've never used
> Declarative Services. I've started reading up on the topic and started to
> ask my self some questions with respect to how I currently do things:
> - Are there any real benefits in using Declarative Services?

yes.  You can set up your services declaratively, including all the references.  For instance
you don't need a service tracker for each service you want to use.  It's very compact yet
powerful. Unlike blueprint, it fits osgi very well, as  the basic unit of configuration is
a service.  (I'm not really familiar with IPOJO).

> - How does Declarative Services "integrate" with the the Configuration
> Admin?

Really well, although it's not explained well in the specs.  Basically you can get ManagedService
or ManagedServiceFactory functionality for your DS component by specifying a configuration
pid (or using the default), specifying configuration policy required, and supplying a configuration
with the pid or a bunch of configurations with factoryPID equal to the component pid.. If
you include a modified method when the configuration is updated your component will be notified,
otherwise it will be deactivated and reactivated with a new instance.  If your component exposes
a service then the configuration properties are exposed as service properties (except for
private properties starting with '.').  Felix DS has some extensions proposed for the next
DS spec so that your component can modify the service properties easily from lifecycle methods.
> - How does Declarative Services "integrate" with the the Dependency Manager

I don't know what the Dependency Manager is, but DS manages all the service dependencies from
references itself.

hope this helps
david jencks

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