The filesize should not be 0. This would mean that the jar files are empty. And without the jar files the java code would break. Compare the userlib on your own disk with the one on the server. They should match.
The requiredlib files are an indicator which module a certain jar file belongs. This makes it easier to administrate jars, in case of removing a module from your app.
You will find a .jar and an associated .requiredlib file in your userlib map.
This is nothing to be concerned about, you could even remove those requiredlib files if you want, as they aren't used by your application.