Java checksum md5 on a file situated on a FTP server

Question

I got a program which needs to compare a file that situated on the Local disk and one on a FTP server. I've decided to go with md5 checksum. I am able to do it with the local file, but I am having problems with the ftp one. Also, I am using Apache FTPClient common.

MessageDigest digest = MessageDigest.getInstance("MD5");

        FileInputStream is = new FileInputStream(FTP_listFiles[i]); //ERROR HERE   
                                                                    //FTP_files is a FTPFile from FTPClient apache commons.
        byte[] buffer = new byte[8192];
        int read = 0;
        try {
            while( (read = is.read(buffer)) > 0) {
                digest.update(buffer, 0, read);
            }
            byte[] md5sum = digest.digest();
            BigInteger bigInt = new BigInteger(1, md5sum);
            String output = bigInt.toString(16);
            System.out.println("MD5: \n" + output);
        }
        catch(IOException e) {
            throw new RuntimeException("Unable to process file for MD5", e);
        } finally {
            try {
                is.close();
            }
            catch(IOException e) {
                throw new RuntimeException("Unable to close input stream for MD5 calculation", e);
            }
        }

NB: If impossible, do you know any equivilant to md5 but can do the same?

Answer 1

What are trying to achieve? Are.you aware that to compute the md5 locally, you will need to download the full file ?

There is a special ftp extension that provide a server-side md5 to the client but it'd not generally supported. Some server also implement some similar proprietary functionality; you''ll have to check for your specific server.

You may want to have a look at the XCRC or XMD5 or XSHA1 commands, for example.