ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
URL url = classLoader.getResource(\"com/x/y/z.cfg\");
File file = new File(url.getPath());
You can't create a File instance, because the only file you have is the JAR. That's why getResource() returns URL. You can get stream by using URL.openStream() method to read contents.
When file is bundled inside the jar then it become byte stream instead of a normal File object.
Try
InputStream stram=getClass().getClassLoader().getResourceAsStream(relativePath);
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