In JDK-6957241, it describes the bug with URLClassPath.findResources.
With JarIndex, URLClassPath.findResources only returns 1 URL.
There are some discussions about the issue in https://github.com/openjdk/jdk/pull/5316 and https://github.com/openjdk/jdk/pull/5383
Currently, There was agreement on dropping the support from the URLClassLoader implementation but it was suggested that it should be disabled for a release or two before the code is removed. A system property can be used to re-enable.
The JBS is to disable JarIndex support in URLClassPath.