Java Classloader - how to reference different versions of a jar

This is a common problem. I'm using 2 libraries A.jar and B.jar and these depend on different versions of the same jar.
Let's say that at runtime I need THIS.x.x.x.jar

MY.jar   
     -> A.jar -> THIS.1.0.0.jar
     -> B.jar -> C.jar -> THIS.5.0.0.jar

I can compile the specific jar (A.jar/B.jar) against its dependency but at runtime I've to load only 1 version. Which one?
Loading only 1 dependency (the latest version) means that my code will probably throw runtime exceptions if the libraries are not Backward Compatible (are there Backward Compatible libraries out there?).

Anyway I know that something like OSGi can fix this issue.
I'm wondering what's the old way to fix this kind of problems...

Thanks a lot