In Java, how do I convert a byte array to a string of hex digits while keeping leading zeros? [duplicate]

Answer 1

This what I am using for MD5 hashes:

public static String getMD5(String filename)
        throws NoSuchAlgorithmException, IOException {
    MessageDigest messageDigest = 
        java.security.MessageDigest.getInstance("MD5");

    InputStream in = new FileInputStream(filename);

    byte [] buffer = new byte[8192];
    int len = in.read(buffer, 0, buffer.length);

    while (len > 0) {
        messageDigest.update(buffer, 0, len);
        len = in.read(buffer, 0, buffer.length);
    }
    in.close();

    return new BigInteger(1, messageDigest.digest()).toString(16);
}

EDIT: I've tested and I've noticed that with this also trailing zeros are cut. But this can only happen in the beginning, so you can compare with the expected length and pad accordingly.