I've been thinking about plugingroups and I'm wondering why we need to
make them very much different than regular plugins.
We've been primarily focused on plugingroups as a way of simplifying the
creation of a custom server assembly. That's a good use of
plugingroups. However, perhaps it isn't the only use. Because we've
been primarily thinking of them as server assembly bits we've been
looking to remove some of the regular plugin functions from them ...
like the classloaders they create and their entries in config.xml.
So the question is; can plugingroups be used in other ways and would the
classloaders, etc... be useful in those other scenarios?
Perhaps a user or solution provider has a need to create a core set of
plugins and then "bundle" them together into higher function
plugingroups (just as we want to do with the server bits). Their
customers could then create their own applications and include
dependencies on these plugingroups. These plugingroups might also be of
value for a user to install on a server independently. I think our
users could also benefit from this by creating dependencies on our
plugingroups rather than individual plugins. A user could create an
application that requires tomcat, web services with cxf, and jms. It
would be nice if they could reference the plugingroups as dependencies
when building a plugin via maven rather than having to reference the
individual plugins.
IIUC, our current direction is that a user would deal with one set of
components (plugingroups) when building a server ... but a different set
of components (plugins) when creating their own application plugin (at
least I think that would be the case). Also, I suspect we would have to
include additional capabilities in Geronimo to protect against a user
attempting to add a dependency on a plugingroup. I'm concerned that
making the plugingroups too specialized results in more work for us and
less capability for the end user.
If we just let the regular processing occur for plugins that aggregate
other plugins (plugingroups), then I think the user could leverage the
plugin groups in many different ways and we'd have fewer issues.
How we actually work the internal details to construct classloaders
could still be enhanced to eventually "skip" the aggregate objects and
drill to the next level for plugingroups ... but I think that's really
an independent issue and an optimization.
So, the proposal I was thinking of was simply this:
1) Create plugin groups as any other plugin and let our current
processing deal with them as any other plugin. The classloader that is
created might actually be useful. The config.xml entry probably is not,
but is it really causing any problems?
2) Use the plugin group attribute more as a way of classification rather
than function enhancement (at least for now). We can always decide to
leverage this knowledge more completely to optimize classloader
construction or for other purposes such as organization.
3) Leave the assembly construction GUI/commandline and plugin install
GUI/commandline to work with plugins only ... no differentiation with
plugingroups.
4) To help clear the clutter from those GUIs/commandlines (one of the
primary motivations in the recent effort) we could create different
plugin catalogs. The default catalog could primarily include the
plugingroups and perhaps a few specific plugins that don't merit further
aggregation. An expert catalog would be the complete catalog with all
plugins included. These same catalogs would be used when installing
plugins and constructing server assemblies so there would be some
consistency for the user.
5) The same set of plugins and plugingroups would be available as
dependencies when a user builds their own plugin via maven.
I think this would broaden the usefulness of plugin groups.
thoughts?
BTW, why are the current plugingroups jars rather than cars ... and why
don't they appear in the geronimo-plugins.xml?
Joe
