Playing with OSGI and JPA

I've been writing an IRC bot for fun, but it's far from being done. My goal is to experiment with JPA in an OSGI environment.


At work, I am using Hibernate, XDoclet to generate the XML and JPA isn't coming soon :-). My last JPA application was a pastebin application, with Wicket, hibernate search, Lucene, etc.

I'm using a friend's library Jerklib with Dynamic JPA. I'm still having some minor issues when deploying but I'll probably find a solution soon.

About the application
Environment
I have a multi-project with Maven and I'm using the maven bundle plugin and I'm developing in Eclipse 3.5 on Debian testing.
I'm using openjpa , dynamic jpa and couple of other dependencies

Design overview
a) Commands implemented as plugins : The bot has a set of factoids(learn, forget, etc...). Each command gets created using a factory.

// message listener //String operation = getOperation();
CommandFactory factory = ServiceFromOSGI.getCommandFactory(operation);

// if the factory is not null, redundancy for the operation parameter
// as a factory can have multiple commands
Command command = factory.createCommand(operation);
ircChannel.say(command.render(ircMessageContext));

b) The command service listens for removal or installation of commands and updates itself.

After writing couple of "users' commands", I would need to implement some administration commands(load/unload plugins, irc specific tasks, etc.).

Problems
The dynamic discovery is failing for now, the persistence provider class is not resolved, it might just be a bundling problem for openjpa. I wrapped it myself.

Conclusion
It's strange that many open source projects still don't provide an OSGI manifest. The maven-bundle plugin is very trivial to use for maven enabled project and there's still bnd.
While OSGI is an interesting technology, I personally don't know anybody using it in the enterprise unless they are an Eclipse shop. I think that it's mostly due to
  • the lack of "OSGI enabled jars"
  • the fear that OSGI might introduce unnecessary complexity
  • the lack of step by step complete examples(if possible with screencasts)

There's plenty of documentation about OSGI and lots of successful applications(Web, Desktop) using OSGI. Hopefully my bot will be one those applications :-)

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