Great stuff. I am amazed at how well you navigated the logback jungle.

I reiterate my earlier question. When the class name of the component factory is passed as a string, logback needs to instantiate the component factory itself. This approach you seems to suffer from the same problem that it tries to solve. The custom ComponentFactory may need to be loaded by a class loader unreachable by logback's own class loader. In any case, the setComponentFactory method in Context should take a ComponentFactory instance, not a string of the factory name. It's just more efficient and is a small change with respect to what you developed already.