Classloader issues - How to determine which library versions (jar-files) are loaded

Question

I\'ve just solved another *I-though-I-was-using-this-version-of-a-library-but-apparently-my-app-server-has-already-loaded-an-older-version-of-this-library-*issue (sigh).

Answer 1

In the current version of Java, library versioning is a rather wooly term that relies on the JAR being packaged correctly with a useful manifest. Even then, it's a lot of work for the running application to gather this information together in a useful way. The JVm runtime gives you no help whatsoever.

I think your best bet is to enforce this at build time, using dependency management tools like Ivy or Maven to fetch the correct versions of everything.

Interestingly, Java 7 will likely include a proper module versioning framework for precisely this sort of thing. Not that that helps you right at this moment,