import static java.nio.charset.StandardCharsets.*;

import java.io.File;
import java.nio.file.Files;
import java.nio.file.attribute.UserDefinedFileAttributeView;

public class Main {

    public static void main(String[] args) throws Exception {
        File f = new File("test.txt");
        f.createNewFile();

        UserDefinedFileAttributeView xattr = Files.getFileAttributeView(f.toPath(), UserDefinedFileAttributeView.class);
        xattr.write("x", UTF_8.encode("1"));
        System.out.println(xattr.list());
        System.out.println(xattr.size("x"));
    }

}