Uniquely identify file in Java

Question

Im on Linux and my Java application is not intended to be portable.

I'm looking for a way to identify a file uniquely in Java. I can make use of statfs syscall since the pair (f_fsid, ino) uniquely identifies a file (not only across a file system) as specified here: http://man7.org/linux/man-pages/man2/statfs.2.html

The question is if it is possible extract fsid from Java directly so I can avoid writing JNI function?

inode can be extracted with NIO, but how about fsid? inode and fsid comes from different structure and are operated by different syscalls...

Answer 1

This java example demonstrates how to get the unix inode number of a file.

import java.nio.file.*;
import java.nio.file.attribute.*;

public class MyFile {

  public static void main(String[] args) throws Exception  {

    BasicFileAttributes attr = null;
    Path path = Paths.get("MyFile.java");

    attr = Files.readAttributes(path, BasicFileAttributes.class);

    Object fileKey = attr.fileKey();
    String s = fileKey.toString();
    String inode = s.substring(s.indexOf("ino=") + 4, s.indexOf(")"));
    System.out.println("Inode: " + inode);
  }
}

The output

$ java MyFile
Inode: 664938

$ ls -i MyFile.java 
664938 MyFile.java

credit where credit is due: https://www.javacodex.com/More-Examples/1/8

Answer 2

I would suggest the GIT method of hashing the file contents. This is proof against copying and renaming.

Java is supposed to be platform independent so using Unix specific methods may not be what you want.