toHMACsha256.java

import java.lang.Math;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;


// one class needs to have a main() method
public class HelloWorld
{
  // arguments are passed using the text field below this editor
  public static void main(String[] args)
  {
    System.out.print(encode("salt", "john"));
    
  }
  
  public static String encode(String key, String data) {
    try {
        Mac hmac = Mac.getInstance("HmacSHA256");
        SecretKeySpec secret_key = new SecretKeySpec(key.getBytes("UTF-8"), "HmacSHA256");
        hmac.init(secret_key);
        return new String(toHexString(hmac.doFinal(data.getBytes("UTF-8"))));
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}
  
  
    public static String toHexString(byte[] ba) {
        StringBuilder str = new StringBuilder();
        for (int i = 0; i < ba.length; i++) {
            String hex = Integer.toHexString(0xFF & ba[i]);
            if (hex.length() == 1) {
                str.append('0');
            }
            str.append(String.format("%x", ba[i]));
        }
        return str.toString();
    }
  
}