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

If you happen to be using JBoss, there is an MBean (the class loader repository iirc) where you can ask for all classloaders that have loaded a certain class.

If all else fails, there's always 'java -verbose:class' which will print the location of the jar for every class file that is being loaded.

If you've got appropriate versions info in a jar manifest, there are methods to retrieve and test the version. No need to manually read the manifest.

java.lang.Package.getImplementationVersion() and getSpecificationVersion() and isCompatibleWith() sound like they'd do what you're looking for.

You can get the Package with this.getClass().getPackage() among other ways.

The javadoc for java.lang.Package doesn't give the specific manifest attribute names for these attributes. A quick google search turned it up at http://java.sun.com/docs/books/tutorial/deployment/jar/packageman.html

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,