> -----Original Message-----
> From: Niclas Hedhman [mailto:[EMAIL PROTECTED]
> Sent: Monday, January 19, 2004 8:58 PM
> To: Avalon framework users
> Subject: Re: [Merlin] Listener best practices
>
>
> On Monday 19 January 2004 11:01, Stephen McConnell wrote:
> > Olaf Bergner wrote:
> > > Are there any best practices for doing what I am trying to achieve?
> > > Currently, I am thinking about writing a lifecycle extension
> to that end.
> > > Is this a feasible solution? Or even better, does anybody
> have a working
> > > solution?
> >
> > Take a look in merlin cvs.
>
> 1. Does it matter if the Service exposes add/remove listener methods?
> 2. Does the Listener explicitly know about the service producing
> the events?
> 3. If so (no on 1, and yes on 2), I think the JavaBeans approach
> is more than
> adequate.
>
> If one want to a weaker coupling, i.e. the listener doesn't know
> what sources
> exists and the producer doesn't manage its listeners, similar to
> what exists
> in OSGi.
> Basically, for a given EventType one can register itself with the
> container as
> either a Consumer or Producer. Each doesn't need to know of each
> other, and
> when an event is fired, the Producer sends it to the container and the
> container will distribute it to the Consumers.
> I think this is a great pattern!!!
>
> Can this be implemented without support of the Container??
>
> YES. You need to create a Service that is an EventRouter, where
> you register
> the EventType you want to listen to, and where event producers fire its
> events to. At the moment, Merlin doesn't support "lookup all
> components that
> implement a particular interface" but if it did, the EventRouter
> would just
> register itself to all known <EventType>Producers.
> So, either the producer components needs to know explicitly about this
> pattern, or the EventRouter needs to be partly implemented as a LifeCycle
> Extension.
Let's assume merlin would have the equivalent of
public List lookupImplementors(ServiceInterface.class)
What you are proposing is
public interface EventProducer
{
addListener(EventConsumer ec);
}
public interface EventConsumer
{
onEvent(Event e);
}
public class EventRouter implements EventConsumer, Initializable,
Serviceable, ...
{
private List m_eventConsumers;
private List m_eventProducers;
public service(ServiceManager sm) throws ServiceException
{
m_eventConsumers = sm.lookupImplementors(EventConsumer.class);
m_eventProducers = sm.lookupImplementors(EventProducer.class);
for (EventProducer ep in m_eventProducers)
{
ep.addListener(this);
}
}
public onEvent(Event e)
{
for (EventConsumer ec in m_eventConsumers)
{
ec.onEvent(e);
}
}
}
Does this capture your ideas? If so, it sounds good to me. Reminds me a bit
of the notify() method in JINI's ServiceRegistrar.
>
> Ideally, we bring this up on the dev@ list and discusses the
> introduction into
> Merlin on a more permanent basis.
>
If there's interest in such an extension.
Cheers,
Olaf
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