Re: [equinox-dev] Bundle loading and adapters

[Thomas Watson <tjwatson@xxxxxxxxxx>]

Unfortunately there is not much documentation
lying around with this information.  The Adaptor API should be well
JavaDoc'ed but that does not mean it is easy to understand or get started
with your own adaptor.  I hope to get a document written that explains
the Adaptor API and overall architecture (which is still changing).  This
will probably push me to start one.  Here is an overview of how the
adaptor BundleClassLoaders and the BundleLoaders interact with each other
in the Framework.

The FrameworkAdaptor API is located
in the org.eclipse.osgi project under the source folder core/adaptor.  The
FrameworkAdaptor is responsible for creating BundleData objects for the
Framework.  There is one BundleData object per Bundle installed in
the Framework.  BundleData objects provide the Framework with an API
for access persistent data about a Bundle.  For example, it has methods
to access a bundle's manifest information, install native code, get a bundle
entry from a bundle, etc.  This data is used by the Framework to create
Bundle object.  The BundleData object also has a method to create
the BundleClassLoader for a bundle.  

When the Framework asks a BundleData
object to create a BundleClassLoader it specifies a ClassLoaderDelegate.
 A ClassLoaderDelegate is responsible for finding classes and resources
that are imported from an exported package or from a package that is provided
by a required bundle.  A BundleClassLoader must call the ClassLoaderDelegate
to find a class or resource.  The ClassLoaderDelegate uses the delegating
classloading model that is outlined in the OSGi specification.  For
example, if it determines that a class or resource is imported from an
exported packge then it will delegate the lookup to the BundleClassLoader
of the Bundle that is exporting the package.  Similiarly, if the class
or resource is provided by a required bundle then it will delegate the
lookup to the BundleClassLoader of the required Bundle.  Finally if
the class or resource is not found then it delegates back to the original
BundleClassLoader that made the request to find the class or resource.

The ClassLoaderDelegate is an interface
from the Adaptor API which is implemented by the Framework, not the FrameworkAdaptor.
 The implementation behind the ClassLoaderDelegate is the BundleLoader
class.  The BundleLoader has all the logic that determines what source
(or bundle) will be used to load resources and classes from specific packages.

I hope this helps you get a start.

Thomas Watson

Glyn Normington <glyn_normington@xxxxxxxxxx> Sent by: equinox-dev-admin@xxxxxxxxxxx 03/10/2004 11:03 AM Please respond to equinox-dev

To:        equinox-dev@xxxxxxxxxxx         cc:                 Subject:        [equinox-dev] Bundle loading and adapters

I'm new to navigating round the Eclipse codebase and am interested in the
way the default and Eclipse adapters mesh with the OSGi bundle loaders.
I've started reading the code, but I'd be really interested to know if
there are snippets of information lying around that might save me some
time. I tried searching the archive of this list but didn't find anything
relevant.

Glyn Normington

_______________________________________________
equinox-dev mailing list
equinox-dev@xxxxxxxxxxx
http://dev.eclipse.org/mailman/listinfo/equinox-dev