[rules-users] OSGI, classloading, and imports in KnowledgeBuilder

[msully]

Faron - I think I fixed my problem (and without the PackageBuilder stuff) but
I think I cheated :)

In my BundleListener, when I find a Bundle with an .rf file I want to
compile, I do this:
Create an instance of a new Classloader that first delegates class loading
to my BundleListener's Bundle, and if that fails, delegates to the .rf files
Bundle.  I pass this class loader in using a KnowledgeBuilderConfiguration.


			BundleClassLoader bclassLoader = new
BundleClassLoader(bundleContext.getBundle(), bundle);
			KnowledgeBuilderConfiguration conf = 
				KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(null,
bclassLoader);
			KnowledgeBuilder kbuilder =
KnowledgeBuilderFactory.newKnowledgeBuilder(conf);


The Classloader looks much like yours, but each overridden call looks like:


   protected Class<?> findClass(final String name) throws
ClassNotFoundException {
    	try {
    		Class<?> clazz =  primeBundle.loadClass(name);
    		return clazz;
       	} catch (ClassNotFoundException c) {
    		if (secondBundle != null) {
        			 Class<?> clazz2 = secondBundle.loadClass(name);
        			 return clazz2;
    		} else {
    			logger.info("Second is null");
    			throw c;
    		}
       	}
    }



Now only my bundles containing rules need to import the classes they need -
my bundle containing the 'FlowManager' that wraps the call to perform does
not.  It allows my core Flow bundle to be totally agnostic to the data
processed in it, while its clients, WorkItemHandlers and flow definition
bundles only import the classes they need.  Hopefully this is a lasting
solution - my Drools usage isn't very complex right now.

I imagine I'd have to get a little more complex if I were to use any
abilities where Drools had to create instances of my domain objects at
process time, but right now that is all handled by WorkItemHandlers that are
registered as services from their own bundles.

Mark - I'd love to help, but I'm just starting with Drools and OSGi right
now, so I'm not sure I know enough yet.

Mike
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