Yesterday evening we had a
BoF session at ApacheCon about
OSGi.
OSGi is getting hot at Apache. Cocoon decided a few weeks ago to go that route to finally implement "
real blocks" which have been our goal for more than 2 years. The
directory project is considering using it and
Alex Karasulu invited the
Oscar project to join the
ASF. And we see other projects interested in using OSGi as well such as
James.
Why is it hot? It the service container landscape, OSGi fits inbetween heavyweight J2EE servers and ligtweight containers such as Excalibur, Spring or Pico. It provides among other things classloader isolation and hot deployment or remote application blocks (called "bundles").
There have been numerous attempts at writing such a container at Apache, either in Avalon (Fortress, Merlin) or Cocoon (the "kernel") but this always ended up to be either one-man shows or leading to fights about the container specification. This is what caused the death of the
Avalon project. OSGi brings a solution to these social problems as it is developed elsewhere. We can't fight on the container specification, as it's already there. We just have to use it. And up to now, it happens to fulfill Cocoon needs and goals quite nicely.
Also, most projects needing such kind of container don't have the time nor willingness to write their own. OSGi has several implementations (both commercial and OSS) that are solid and stable and can be used right now.
One of the problems raised during the initial discussions about having Oscar joining the ASF were licence issues, as the R3 specification (the current version) doesn't have a real licence. Now Eclipse 3.1 heavily uses OSGi for its plugin architecture, using some features that will be in the upcoming R4 specification. And they happen to have already
solved this issue, as the R4 API code will be released under the
EPL.