// If providers is empty, add the known providers. This can happen when
// executing this code in the presence of an unsupported URL type (like
// bundleresource).
if (providers.isEmpty()) {
providers.add(new ByteMapListingProvider());
providers.add(new DirectoryListingProvider());
providers.add(new EmbeddedJarListingProvider());
providers.add(new JarListingProvider());
}
}