I read the blog entry and discussion. The entire discussion is
predicated on the idea that osgi is close to ideal as-is and we have
no need to consider any other point of view. If you step back a bit I
see two things clearly acknowledged by everyone:
1. its useful to be able to know what classes are needed to make a jar/
bundle/plugin/module work and which classes are expected to be used
elsewhere
2. its essential to know what jars/bundles/plugins/modules are
actually in your running system
In osgi-land, import-package and export-package supply (1), and
require-bundle sort of helps with (2) but AFAICT right now doesn't
support "artifact aliasing"
In maven-land, the pom dependency tracking provides a pretty good
solution for (2), including some support for overriding "requirements"
through exclusions, but it's single-classloader model doesn't
translate directly into an app server or osgi runtime
In geronimo trunk we emphasize (2) and can actually assemble working
servers using it, and have support for (1) (although its mostly
backwards from osgi specifications)
I'd say that in my (limited) experience osgi zealots typically think
that (1) is essential and brush (2) under the carpet by working in
constrained environments such as their eclipse workspace. I'd say
that our experience with geronimo is that (1) is rarely needed if you
have a working (2) (look at how many hidden-classes and non-overriable
classes filters are in our poms -- none for the use of geronimo, and a
few to make deploying applications that include the same jars as us
work)
The geronimo/maven approach to (2) is to include the dependency
information with the artifact. I'm not sure what approach(es) osgi is
considering -- OBR appears to not consider bundling dependency info
with the artifact but to have a completely external specification. I
don't know about p2.... but since jason vanZyl seems to be looking at
it I'd guess it is more maven friendly.
If you don't bundle (2) with the artifacts then you need some kind of
import-package to artifact map or resolution system. We sort of have
some vestiges of this today: when you deploy a web app as a geronimo
plugin (or export it from a server where it was deployed) it has
picked up dependencies on jetty or tomcat based on which deployer you
specified in the plugin project pom or which kind of server you
deployed on. Another example is that the car-maven-plugin filters the
view of the local maven repo so only the versions specified in the pom
are visible to the geronimo server we run off the repo -- this allows
you to build plugins for a 2.1.3 server even if you have 2.2-SNAPSHOT
artifacts locally and some of the dependencies don't specify the
version required.
I don't know where the best balance for geronimo lies here. I
certainly think claiming all we need is import-package is
shortchanging most of our experience in producing geronimo as a
working server.
thanks
david jencks
On Mar 13, 2009, at 7:10 AM, Lin Sun wrote:
I think I was not too clear below. I didn't mean to say that I am in
favor of Require-Bundle because it is a lot harder to come up with the
right Import-Package lists. What I meant was that the reason why a
lot of people are using Require-Bundle like David mentioned in his
early notes is probably because it is a lot easier to use.
I personally had to spend quite some time to figure out the prob I
mentioned earlier - I was developing a bundle that needs to import
the javax.transaction package from the transaction in OSGi bundle, but
two bundles have it (the basic OSGi J2SE and the transaction in OSGi
bundle). I was able to resolve this using Import-Package with the
specific version of javax.transaction package that I need. I just
tried to switch to use Require-Bundle, that is to have my bundle to
depend on the transaction in OSGi bundle as it contains the right
version of the javax.transaction package I need, but my bundle is
broken completely due to CDNFE. I don't think the Require-Bundle
offers the fine grain control that I needed for my bundle and I am
sure Geronimo would have a lot more complicated bundles than what I
was developing.
BTW, there's a good discussion here:
http://thhal.blogspot.com/2008/02/dependencies-and-package-
imports.html
- in particular in the first comment from Neil Bartlett and the
limitations of Require-Bundle documented in the OSGi v 4.1 core spec
(section 3.13.3).
Lin
On Thu, Mar 12, 2009 at 11:40 PM, Lin Sun <[email protected]>
wrote:
Not sure about Require-Bundle. I personally has never used it and I
never see it is being used in the OSGi repo. Require-Bundle may not
offer the level of control that the Import-Package provides but it is
probably a lot harder to come up with the right Import-Package lists.
I think this scenario should work just fine if using Import-Package.
