Java access files in jar causes java.nio.file.FileSystemNotFoundException

A FileSystemNotFoundException means the file system cannot be created automatically; and you have not created it here.

Given your URI, what you should do is split against the !, open the filesystem using the part before it and then get the path from the part after the !:

final Map<String, String> env = new HashMap<>();
final String[] array = uri.toString().split("!");
final FileSystem fs = FileSystems.newFileSystem(URI.create(array[0]), env);
final Path path = fs.getPath(array[1]);

Note that you should .close() your FileSystem once you’re done with it.