MD5.java

import java.io.FileInputStream;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
 
public class MD5 {
    public static String getMD5(String input) {
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            byte[] messageDigest = md.digest(input.getBytes());
            BigInteger number = new BigInteger(1, messageDigest);
            String hashtext = number.toString(16);
            // Now we need to zero pad it if you actually want the full 32 chars.
            while (hashtext.length() < 32) {
                hashtext = "0" + hashtext;
            }
            return hashtext;
        }
        catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
    }
 
    public static void main(String[] args) throws NoSuchAlgorithmException {
        System.out.println(getMD5("Hello world")); // your string data goes here 
    }
}

MD5ForFiles.java

import java.io.FileInputStream;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
 
public class MD5ForFiles {

     public static void main(String[] args)throws Exception {
        MessageDigest md = MessageDigest.getInstance("MD5");
        FileInputStream fis = new FileInputStream("F:\\hey.txt"); //give your path here 
        byte[] dataBytes = new byte[1024];
        int nread = 0;
        while ((nread = fis.read(dataBytes)) != -1) {
          md.update(dataBytes, 0, nread);
        };
        byte[] mdbytes = md.digest();
        
        //convert the byte to hex format method 1

        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < mdbytes.length; i++) {
          sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
        }

        System.out.println("Digest(in hex format):: " + sb.toString());
        
        //convert the byte to hex format method 2

        StringBuffer hexString = new StringBuffer();
    	for (int i=0;i<mdbytes.length;i++) {
    		String hex=Integer.toHexString(0xff & mdbytes[i]);
   	     	if(hex.length()==1) hexString.append('0');
   	     	hexString.append(hex);
    	}
    	System.out.println("Digest(in hex format):: " + hexString.toString());
    }
}

This is one of the way to generate unique tokens for any types of files,photos,text data.

MD5

1. Message-Digest (Fingerprint) algorithms are special functions which transform input of (usually) arbitrary length into output (so-called "fingerprint" or "message digest") of constant length.

2. MD5 algorithm takes input message of arbitrary length and generates 128-bit long output hash.

3. Message-Digest algorithms serve in digital signature applications for guaranteeing consistency (integrity) of data.

There are various alternatives to MD5 which can be used.