Since its inception, my project has been using DiscoveryV1 and we've
never dealt with Jini constraints. Peter's comments last week about the
flexibility of DiscoveryV2 inspired me to learn more about it and to
experiment a bit. To my surprised, I found it very difficult to figure
out how to turn V2 on (I ended up reading a lot of source code), and it
looks like it's nearly impossible to migrate in a backward compatible
way, i.e. continuing to fully interact with services that were deployed
with the default preference for V1. I would LOVE to be told that I've
made a mistake or missed something important...
* To switch Reggie to use V2 for multicast announcements:
com.sun.jini.reggie {
discoveryConstraints = new BasicMethodConstraints(new
InvocationConstraints(null, DiscoveryProtocolVersion.TWO));
}
* To switch group discovery to use V2 for multicast requests:
net.jini.discovery.LookupDiscovery {
discoveryConstraints = new BasicMethodConstraints(new
InvocationConstraints(null, DiscoveryProtocolVersion.TWO));
}
* To create a locator that uses V2 for directed unicast discovery:
new ConstrainableLookupLocator(host, port,
new BasicMethodConstraints(new InvocationConstraints(null,
DiscoveryProtocolVersion.TWO)));
* To tell DiscoveryV2 how to encode and decode the messages, create a
file called
"META-INF/services/com.sun.jini.discovery.DiscoveryFormatProvider" and
put in lines (for example):
com.sun.jini.discovery.plaintext.Client
com.sun.jini.discovery.plaintext.Server
However (and this is the key problem), any deployed clients or Reggies
which lack the
META-INF/services/com.sun.jini.discovery.DiscoveryFormatProvider file
will not be able to decode the incoming messages and will drop them with
an error message about unknown format IDs.
So, the only solution I can see is to start shipping new services with
the DiscoveryFormatProvider file in place, and then wait several
releases until all of my old deployments have been retired, and then
turn on the V2 preference. Am I wrong? Is there a trick to get
already-deployed clients to use a format ID that they don't know about?
Surely other people have had similar problems deploying brand-new
DiscoveryFormatProvider implementations?
Is there a way to make services send out both V1 and V2 multicasts? Is
there a way to tell LookupDiscovery.UnicastDiscoveryTask to try V2 first
and then retry with V1?
I feel like I'm missing some central point...
Chris
