I'm trying to understand what happens when non-bundle parts of a program depend on bundles-as-JARs, and these same bundles are used by other bundles as well. Let me try to make sense of this with an example.
I have few bundles that use the org.apache.felix.log bundle. They post log messages to the LogService. My application itself (the part with a main() method that starts up Felix) also uses the org.apache.felix.log /JAR/, as it tracks the LogReaderService and listens with a LogListener implementation. In order to start up my main program, I must either include the org.apache.felix.log JAR in the main JAR or at least point to it on the class path. In order for the other bundles that depend on the logging facility to work right, I was also installing and starting the org.apache.felix.log bundle. It occurred to me that if my main program is already loading up this log-related JAR, it should add the packages already exported by the org.apache.felix.log bundle to the org.osgi.framework.system.packages property supplied to Felix.start(). If I understand this property correctly, adding exported packages to it makes things as though these packages are built into Felix itself (or, rather, the system bundle). Going one step further, I should add the org.apache.felix.log.impl.Activator to the BundleActivator list supplied to Felix.start(). I only realized I had to modify the org.osgi.framework.system.packages property after I tried loading the org.apache.felix.log bundle, then noticed that my program encountered ClassCastExceptions when casting from, say, org.apache.felix.log.impl.LogReaderServiceImpl to org.osgi.service.log.LogReaderService. That must mean that the log-related classes were pulled in by two different class loaders -- one for the main program, and another seen by the bundles using the log bundle. Trying to figure out how to transfer a bundle's Export-Package header to the org.osgi.framework.system.packages property just feels wrong -- invasive and brittle. On the other hand, I don't see how Felix could figure these exports out on its own. The question comes down to this: Is it a poor design to try using a bundle from a normal, "non-bundle" portion of a program, even when there are other bundles in the system that will use this same bundle? If I use the bundle code from my "non-bundle" program, should I not load the actual bundle within Felix? Or should I factor this "non-bundle" program into a bundle itself, and have it use the log bundle like all the other bundles? My language is muddled, but I hope the problem in question is clear enough to provoke a response. -- Steven E. Harris
