How to create checksum of a file?

To generate a hash or checksum of a file, below is the implementation shows how do we need to read a file’s bytes in chunks and calculate the checksum.

Code:

public String getFileChecksum(MessageDigest digest, File file) throws IOException

            {

                //passing file to get FileInputStream

                FileInputStream fis = new FileInputStream(file);

                

                //create a byte array to read file content in bytes

                byte[] byteArray = new byte[1024];

                int bytesCount = 0;

                 

                //read the bytes of a file to update the message digest function of MD5 algorithm

                while ((bytesCount = fis.read(byteArray)) != -1) {

                    digest.update(byteArray, 0, bytesCount);

                };

                

                //close the stream

                fis.close();

                

                //get the checksum bytes

                byte[] bytes = digest.digest();

                

                //the bytes are in decimal format & convert them to hexadecimal

                StringBuilder sb = new StringBuilder();

                for(int i=0; i< bytes.length ;i++)

                {

                    sb.append(Integer.toString((bytes[i] & 0xff) + 0x100, 16).substring(1));

                }

                

                //return complete checksum value

               return sb.toString();

            }

We can also use above method like below to generate MD5 checksum :

//Create checksum for this file             File file = new File("c:/temp/testFile.txt");                           //create instance of MD5 algorithm             MessageDigest md5Digest = MessageDigest.getInstance("MD5");                           //Get the hash/checksum             String hash = getFileHash(md5Digest, file);                           //see checksum             System.out.println(hash);