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From Rick McGuire <rick...@gmail.com>
Subject Converting classloaders to BundleContexts
Date Tue, 20 Oct 2009 11:58:22 GMT
I just started taking a look at converting the Tomcat plugon to the 
brave new OSGi world, and immediately ran into a problem that's likely 
to be a fairly generic problem that other plugins might also have.  In 
the method TomcatManagerImpl.getConnectorConfiguration(), there's the 
following code that causes a compilation error:

        try {
            kernel.loadGBean(gbeanData, container.getClass().getClassLoader());
            kernel.startGBean(name);
        } catch (Exception e) {
            log.error("Error when adding new tomcat connector" + uniqueName, e);
        }


the loadGBean() method now takes a BundleContext rather than a 
classloader, so there's a signature error.  The container is an object 
that implements the WebContainer interface (either the Tomcat or Jetty 
version).  The intent here is to load some GBeans using the container 
object's configuration context via its classloader.  In order for this 
to work now, getConnectorConfiguration() will need to somehow obtain the 
container's BundleContext rather than a class loader.  This is something 
that's not easily done at the moment.  I see a couple of potential 
solutions:

1)  Make the WebContainers context aware and add a getBundleContext() 
method to the WebContainer interface. 
2)  Use the BundleReference interface introduced in the 4.2 OSGi 
framework to obtain the bundle from the object's defining classloader.

I suspect that 1) is the cleaner solution.  2) has a potential downside 
that it depends on the WebContainer implementation class being located 
within configuration bundle.  A restructuring of the bundles to improve 
modularity could potentially cause this to fail, which would not really 
be a solid structure.

I think I've convinced myself that 1) is the correct approach, but 
thought this was something worthing of raising as a discussion point on 
the dev list.

Rick

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