code: static String [] searchJarFSForClasses( URL url ) throws IOException {
          try {
              try {
                  FileSystems.newFileSystem(url.toURI(), new HashMap<>());
              } catch (FileSystemAlreadyExistsException e) { /* ignore */ }
  
              Path path = FileSystems.getFileSystem(url.toURI()).getPath("/");
  
              return Files.walk(path).map(Path::toString)
                      .filter(BshClassPath::isClassFileName)
                      .map(BshClassPath::canonicalizeClassName)
                      .toArray(String[]::new);
          } catch (URISyntaxException e) { /* ignore */ }
          return new String[0];
      }
docs: Search jar file system for classes.
  @param the jar: file system url
  @return array of class names found
  @throws IOException