Ian,
Very interesting thoughts for this.
I think it would be more work and would complicate your
ServiceLocator beyond what is needed.
The problem you speak of to me seems more like a deployment time
consideration. Thus, may be best handled via the application assembler role.
The application assembler should determine which version of the services to
use as part of the application functionality and create the application
archive (.ear) containing those correct service jars. If your services are
backed by EJBs, I have never tried to deploy multiple applications with the
same, or different EJB versions, possibly bound to the same physical JNDI
name. It would be curious to see how well container providers support this
scenario, could they even deploy 2 or more instances of the same EJB.
Unless you intend to have the capability in code to switch between
versions of EJB interfaces. In this case, you would still need some kind of
Factory pattern to determine the correct version of the service to use
anyway (to keep the client code neutral). So it would seem better to put the
requirement of determining the correct version to the Factory and it can
still gain the benefits of the ServiceLocator pattern for caching and
simplifying the lookup of the services.
Just my $0.02,
Gary
-----Original Message-----
From: Ian Vellosa [mailto:vellosa@(protected)]
Sent: Thursday, August 14, 2003 3:02 AM
To: J2EEPATTERNS-INTEREST@(protected)
Subject: Service Locator for versioned services
Good morning people.
I'm hoping that some of you can help stimulate ideas in my mind with regards
the Service Locator.
After writing an initial application which was all contained in one large
ear, we have recently embarked on a process of splitting up the application
into a number of services each of which have their own ear. Now that the
next application is in development and modifications need to be made to the
base services we would like to deploy different versions of the same
service. So we deploy two ear files.
service-1.0.ear
service-2.0.ear
and within them we have JNDI names something like
/CompanyName/ServiceName/VersionNumber/ejb
I would like to include a properties/xml file as part of the deployment for
my application that says it should use version 1.0 of service X and version
1.3 of service Y etc and have the Service Locator use this file to look up
the correct version of the EJBs.
Have people done or thought about this before?
Are there any resources about that can help me? (I can not find anything on
the Sun Java site)
Does anyone have any words of wisdom for me?
Any help is most appreciated
Thanks in advance
IV
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