Hmm, that sounds like opportunity.
A dedicated codebase service has all the time in the world to burn
processor cycles on analysis, as its main task is simply serving up jar
files over networks.
Bytecode analysis, identifies class, package and possibly module API,
which can be stored with the harvested metadata in mirror objects, one
for each class, package and module. Optional Package metadata could be
a potential source of information too.
Bundles, depend upon and export packages. Once the API is identified
using bytecode analysis, fast comparison using mirror objects could
identify compatibility.
This could be utilised in two ways:
1. As a check of backward compatibility for modules / packages over
different release versions, for substituting later compatible bundle
versions, if desired.
2. When a dependency on a package only utilises a subset of that
package, the actual API requirements may still be satisfied, even though
different release versions of that package may not usually be
interchangeable or fully compatible.
A module or bundle would exist within its own classloader, in the local
jvm. The packages or modules upon which it depends could be made
available from other classloaders.
Bundles could be uploaded to codebase services or a codebase service
could retrieve the bundles from designated repository's, perform
analysis, then make the bundles available in a location independent
manner, to prevent codebase loss and allow for redundant codebase services.
Then all one need do is to upload application bundles to the codebase
server and register a service, the service and bytecode could be
provided independently, the codebase service can provide entire
application bytecode built on Jini services and other third party libraries.
Have a look on springsource, there are many OSGi jar bundles available,
these are simply jar files with Metadata.
Someone's done so much hard work already, why not ride the wave? There
are already support tools available to create application bundle manifests.
The reason I'm considering bundles, is it reduces the number of
classloaders required, one per bundle as opposed to one per package.
One cannot rely on standard java Package meta data to exist in jar files.
********This doesn't require an OSGi framework.*********
http://blog.springsource.com/2008/02/18/creating-osgi-bundles/
http://www.springsource.com/repository/app/bundle?query=A
http://www.springsource.com/repository/app/faq
From the website:
What is the SpringSource Enterprise Bundle Repository?
The SpringSource Enterprise Bundle Repository is a collection of open
source libraries commonly used for developing enterprise Java
applications with the Spring Framework. The repository contains jar
files (bundles) and library definition (".libd") files. A library
defines a collection of bundles that are often used together for some
purpose (e.g. the "Spring Framework" library). There are hundreds of
bundles contained in the repository.
The repository meets the following criteria:
* Every jar file in the repository is a valid OSGi bundle. Any jar
you download from the repository can be deployed as-is into an
OSGi Service Platform and the SpringSource dm Server. It can also
be used as a regular jar file outside of OSGi.
* Every bundle and library has full version information associated
with it. The package export information for a bundle contains
version information, and the package import information for a
bundle contains full version range compatibility information.
* The repository is transitively complete. The mandatory
dependencies of any bundle are guaranteed to also be in the
repository. Most of the optional dependencies of any bundle in the
repository will also be present. The bundles listed in any library
definition are guaranteed to be in the repository.
* The repository is self-consistent. Before any artefact is uploaded
to the repository, we verify that it can be installed, resolved,
and started in an OSGi Service Platform (using the same profile as
the SpringSource dm Server) alongside all of the other bundles in
the repository.
* The repository can be used from Ivy and Maven based builds.
Cheers,
Peter.
Niclas Hedhman wrote:
On Fri, Oct 16, 2009 at 1:04 PM, Niclas Hedhman <[email protected]> wrote:
On Thu, Oct 15, 2009 at 11:53 AM, Peter Firmstone <[email protected]> wrote:
It may be possible to segregate OSGi modules, into separate ClassLoaders
using bytecode dependency analysis and by capturing OSGi metadata.
Unfortunately, this is harder than you might think. OSGi metadata
provides a set of constraints, but often there are multiple solutions
to those constraints, and sometimes the framework is not capable of
resolving those constraints even if there is a solution available,
since exhaustive checks are too expensive for large applications. What
I am trying to say is; Being able to figure out how a particular
framework implementation has wired up the class spaces, just by
looking at the metadata is impossible, and likewise with bytecode
dependency analysis.
One more thing, it even depends on how the OSGi framework is started,
since some packages may be exported from the classpath by the
framework, and on top of that there is bootclasspath delegation
throwing a big wrench into the heap of problems.
Cheers
