jar.getNextJarEntry() never seems to return anything other than null

I18n.java

// I18n.java
// Excerpt for question on StackOverflow
// http://stackoverflow.com/questions/5061554/how-do-i-access-the-content-of-folders-inside-a-jar-file

/**
 * Private implementation method.
 * @return a list containing the locales implemented by the resource bundles
 */
private static List<Locale> getLocaleListFromJar() {
    List<Locale> locales = new ArrayList<Locale>();
    try {
        URL packageUrl = I18n.class.getProtectionDomain().getCodeSource().getLocation();
        JarInputStream jar = new JarInputStream(packageUrl.openStream());
        while (true) {
            JarEntry entry = jar.getNextJarEntry();
            if (entry == null) {
                break;
            }
            String name = entry.getName();
            if (resourceBundlePattern.matcher(name).matches()) {
                addLocaleFromResourceBundle(name, locales);
            }
        }
    } catch (Exception e) {
        System.err.println(e);
        return getLocaleListFromFile(); // File based implementation in case resources are not in jar
    }
    return locales;
}