code: private static FileSystem getJarFs(Path jarFile) throws IOException {
      Path key = jarFile.toAbsolutePath();
  
      synchronized (ZIP_FILESYSTEMS) {
        FsWrapper fs = ZIP_FILESYSTEMS.get(key);
        if (fs == null) {
          fs = new FsWrapper(FileSystems.newFileSystem(key, null), key);
          fs.incrRefCount();
  
          ZIP_FILESYSTEMS.put(key, fs);
        } else {
          fs.incrRefCount();
        }
  
        return fs;
      }
    }
docs: Returns a reference-counted Jar FileSystem, possibly one that was previously returned.