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Which Filesystem JAR Is a Class From?

In my environment, a test was blowing up. In my coworkers, it was working fine. On inspection, it seems my environment was expecting a different version of a class. How do I figure out what JAR the new/incorrect requirements are coming from?

I found this blog post, and it helped me greatly: From which Jar a Class was loaded?

I used this info to write the following utility:

package net.nelz.utils;

import javax.activation.*;

public class ClassFinder {
    public static String findClassOnFilesystem(final String className) {

        try {
            final Class clazz = Thread.currentThread().getContextClassLoader().loadClass(className);

            return ClassFinder.findClassOnFilesystem(clazz);
        } catch (ClassNotFoundException ex) {

            return "Class:" + className + " - CLASS NOT FOUND!";


    public static String findClassOnFilesystem(final Class clazz) {

        final ProtectionDomain pDomain = clazz.getProtectionDomain();
        final CodeSource cSource = pDomain.getCodeSource();

        final URL loc = cSource.getLocation();
        final String result = clazz.toString() + " - " + loc;

        return result;


Additionally, after finding this solution, a coworker pointed me to the Dependency Finder as another tool that can help diagnose classpath issues.