Agree that it is time to start looking at OSGi and thanks for kicking
this off!
-Donald
David Jencks wrote:
Geronimo has been around for a while and despite the many good features
gbeans and the geronimo kernel are not catching on big time. I think we
want to consider taking action now to avoid ending up being dragged down
by supporting a dead container. Here are a few thoughts.
Actual problems with geronimo:
- gbeans are too restrictive. It's too hard to instantiate other
peoples components as gbeans. GBeans don't support common patterns like
factory methods, factory beans, etc etc, and require the component to be
instantiated directly by the gbean framework.
- it's too hard to get the classloaders to work. The most common
problem is a class cast exception due to loading the same jar in two
plugins. NoClassDefFound errors from an optional jar in a child
classloader are also really annoying.
Really good things about geronimo I haven't seen elsewhere (at least in
one place):
- gbean dependencies work across plugins. Dependencies are a unified
system, not per-plugin.
- gbean dependencies are resolved in the ancestors of a plugin, not
server wide. This means that you can't make a partially specified
dependency ambiguous by deploying additional plugins. I consider this
an extremely important feature for predictability.
- plugin dependencies allow assembly of a server from the explicit
dependencies which are normally the same as the maven dependencies.
Other projects and specs that have stuff we should look into:
maven. Maven has a lot better infrastructure for dealing with
dependency resolution from partial transitive dependency specification
than we do. We should look into using more of their infrastructure.
osgi. osgi has a lot of similarities to geronimo. The osgi classloading
model is getting a lot of people excited. The import-bundle idea is
pretty much the same as our classloader model where every jar is a
plugin. I don't know if people are really using the allegedly
recommended method of specifying imports and exports and letting the
osgi runtime figure out where they come from; this seems worth
investigating to me. Also, we get periodic inquiries about when we are
going to support osgi and the was ce folks get even more.
osgi blueprint service (rfc 124) This appears to be a simple wiring
framework for a single plugin. IIUC it uses the osgi service registry
for component dependencies between bundles.
xbean-spring. I'd be reluctant to try to implement a blueprint service
that didn't provide the xbean-spring capabilities really well
ee6 dependency injection. EE6 is going to have a pretty sophisticated
dependency injection service which we'll need to support anyway. We
should try to figure out how much of the core we can assemble using it.
Other great stuff we have:
xbean-reflect, xbean-finder, xbean-spring
These ideas have been floating around in my head for a long time and
I've chatted with various people about them occasionally. While more
discussion is certainly needed on everything here I need to do some
implementation to understand much more. So, what I'm planning to do:
Dave's crazy work plan...
- Try to use the osgi classloader. I think this involves putting the
classloader creation in Configuration into a service. Configurations
will turn into osgi bundles. I'll put the Kernel in the osgi
ServiceRegistry so the Configuration bundle activator should be able to
use it to resolve cross-plugin dependencies.
- try to figure out how maven dependency resolution fits into osgi.
- see if eclipse p2 is relevant for provisioning geronimo repositories
at this point I think geronimo would be running on osgi, still using
gbeans.
- look into relaxing the gbean framework so it is more plugin-at-a-time
rather than gbean-at-a-time
- see how that differs from the blueprint service, ee DI, and
xbean-spring. Try to support all of these at once.
Thoughts? Counter proposals? Anyone interested?
many thanks
david jencks
