Java: How to search duplicate files in a folder not only by name ,but also by size and content?

Question

I want to create a Java application to identify duplicates. So far I can find duplicates only by name, but I also need size, file type, and maybe content. This is my code so far, using a HashMap:

public static void find(Map<String, List<String>> lists, File dir) {
    for (File f : dir.listFiles()) {
        if (f.isDirectory()) {
            find(lists, f);
        } else {
            String hash = f.getName() + f.length();
            List<String> list = lists.get(hash);
            if (list == null) {
                list = new LinkedList<String>();
                lists.put(hash, list);
            }
            list.add(f.getAbsolutePath());
        }
    }
}

Answer 1

I used MessageDigest and checked some files and find the duplicates according to all the criteria I have listed in the title and description. Thank you all.

private static MessageDigest messageDigest;
static {
    try {
        messageDigest = MessageDigest.getInstance("SHA-512");
    } catch (NoSuchAlgorithmException e) {
        throw new RuntimeException("cannot initialize SHA-512 hash function", e);
    }
}   

and this is the result after implementation in the search code for duplicates

public static void find(Map<String, List<String>> lists, File dir) {
for (File f : dir.listFiles()) {
  if (f.isDirectory()) {
    find(lists, f);
  } else {
      try{
          FileInputStream fi = new FileInputStream(f);
          byte fileData[] = new byte[(int) f.length()];
                fi.read(fileData);
                fi.close();
                //Crearea id unic hash pentru fisierul curent
                String hash = new BigInteger(1, messageDigest.digest(fileData)).toString(16);
                List<String> list = lists.get(hash);
                if (list == null) {
                    list = new LinkedList<String>();
                }
                //Adăugați calea către listă
                list.add(f.getAbsolutePath());
                //Adauga lista actualizată la tabelul Hash
                lists.put(hash, list);

      }catch (IOException e) {
                throw new RuntimeException("cannot read file " + f.getAbsolutePath(), e);
            }

  }
}

}