public static String HMACSHA256(String data, String key) throws Exception { 
 
       Mac sha256_HMAC = Mac.getInstance("HmacSHA256"); 
 
       SecretKeySpec secret_key = new SecretKeySpec(key.getBytes("UTF-8"), "HmacSHA256"); 
 
       sha256_HMAC.init(secret_key); 
 
       byte[] array = sha256_HMAC.doFinal(data.getBytes("UTF-8")); 
 
       StringBuilder sb = new StringBuilder(); 
 
       for (byte item : array) { 
 
           sb.append(Integer.toHexString((item & 0xFF) | 0x100).substring(1, 3)); 
 
       } 
 
       return sb.toString().toUpperCase(); 
 
   }