Hi,
I have a conflict in my design strategy, that I wish to get some feedback on.
Use-case (I take the smallest understandable case I have, so it may seem too
simple to become a component, but the others are not for sure);
An EnergyMeter receives events from some external source (unknown at design
time). It computes various values (Power, Accumulated kWh) and handles life
cycles of physical EnergyMeters (service, calibration and replacements).
It also produces events for activities going on, such as "High Power Limit
reached" and dozens of others.
I package this as an Avalon Block. There will be dozens or more of these
(similar) blocks in an application. Each of these blocks will have several
event sources wired to them, making the number of event sources to 100s.
The event source should be wired by the Deployer.
The event sources are often very small and simple, and I don't think it is
suitable to be Components, although that is possible. I am instead looking
towards ServiceSelector, and simple JavaBeans events.
For the EnergyMeter code, it would mean something like;
ServiceSelector ss = (ServiceSelector) servicemanager.lookup( "IOsystem" );
Channel ch = (Channel) ss.select( "virtual:///EnergySource" );
ch.addChannelListener( this );
But the hardcoded select() statement won't work if there are a lot of
EnergyMeters present. That could be solved by involving the name of the
EnergyMeter used in the Configuration.
Also, the ServiceSelector must have a configuration where it binds the
available Channel instances to the requested virtual channel names.
To me it doesn't look "clean" IoC, as the client is very much involved in the
"wiring", and in other (non-software) component domains, components have no
clue of the wiring/connection process or what sits/connected to the other end
of the connection/wire.
An alternative would be to let a separate ApplicationListener (BlockListener)
do the wiring, which seems more IoC to me. BUT I can't find any way to
configure the ApplicationListener and tell generic listeners how to wire the
components.
Or another logical way to do it, is to create a EventWiringComponent (EWC),
which is much smarter, that has a configuration of;
<wire>
<event>Channel</event>
<source>MySource3</source>
<destination>MyDestination4</destination>
</wire>
which will basically locate the objects and with reflection do;
mySource3.addChannelListener( myDestination4 );
There is a lookup problem with this approach. The .xinfo file of the EWC
requires to have a dependency on ALL roles, which are not known at design
time of the EWC, and would require modification of .xinfo at deploy time.
This is not acceptable.
Finally, that leads me to think of implementing a whole new container, or
extending Phoenix to have a better wiring system, which IMHO is a bit weak.
Are these issues handled better in Fortress or Merlin? (I have previously got
the impression that they are more for "anonymous components", unlike my use.)
Any comments?
Niclas
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