How to find which jars and in what order are loaded by a classloader?

Question

I could not find a clear answer to this question elsewhere, so I'll try here:

Is there some way (programmatic or other) to get a list of JARs/classes loaded by an Application Classloader in the precise order they were loaded? By Application Classloader I mean the classloader that loads an EAR application in an applications server (WLS, WAS, JBoss...), but obviously, it applies to any classloader.

So, to generalize, what I would like to find out is the list and order of JARs loaded by a specified classloader. Not individual classes, that is easy enough to find out by calling the classloader.getPackages(), but a list of JAR files that were loaded by this classloader.

Answer 1

Have you tried to use the JVM option -verbose:class. It displays all loaded JAR files and classes.

Example:

[Opened C:\Program Files\JDK160~1\jre\lib\rt.jar]
[Loaded java.lang.Object from C:\Program Files\JDK160~1\jre\lib\rt.jar]

Answer 2

The short answer is no. Classloaders are not required to expose their search logic.

However, if your classloader instance happens to be URLClassLoader or a subclass, then you do have access to the list of jars/directories, via the getURLs() method. Per the doc for this class, those URLs will be searched in order.

In practice, if you're trying to find out where a class is being loaded from, Steve's answer is probably more useful.