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).

Does anybody know a good way to verify (or monitor) whether your application has access to all the appropriate jar-files, or loaded class-versions?

Thanks in advance!

[P.S. A very good reason to start using the OSGi module architecture in my view!]

Update: This article helped as well! It gave me insight which classes JBoss' classloader loaded by writing it to a log file.

Answer 1

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.

Answer 2

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