How to get numeric groupid/userid using java7 file attribute apis?

I can use the following code to get the name of the owner of a file;

    final PosixFileAttributes basicFileAttributes =
        Files.readAttributes( path, PosixFileAttributes.class, 
                                    LinkOption.NOFOLLOW_LINKS );
    String ownerName = basicFileAttributes.owner().getName();

But I'm also trying to get hold of the numeric unix id of the user in question. In the debugger I can see it's hiding inside "UnixFileAttributes" (subclass of PosixFileAttributes), but is there any reasonably standard way to get hold of it ?