How to use a jaxb.index file

OK, this took quite some digging, but the answer is not that surprising and not even that complicated:

JAXB can't find jaxb.index, because by default, newInstance(String) uses the current thread's class loader (as returned by Thread.getContextClassLoader()). This doesn't work inside Felix, because the OSGi bundles and the framework's threads have separate class loaders.

The solution is to get a suitable class loader from somewhere and use newInstance(String, ClassLoader). I got a suitable class loader from one of the classes in the package that contains jaxb.index, a sensible choice for flexibility reasons probably is ObjectFactory:

ClassLoader cl = my.package.name.ObjectFactory.class.getClassLoader();
JAXBContext jc = JAXBContext.newInstance("my.package.name", cl);

Maybe you could also get at the class loader that the Bundle instance is using, but I couldn't figure out how, and the above solution seems safe to me.

You get that exception when you use the JAXBContext.newInstance(String) factory method, where you pass in the package name as the argument. This does require the ObjectFactory to be there, otherwise, JAXB doesn't know which classes to process.

If you don't have an ObjectFactory, you need to JAXBContext.newInstance(Class...) instead, passing in the explicit list of annotated classes to add to the context.