I have set up a github webhook with content type as application/json and have provided a secret. My java code generates the different hash than what github provides. Any help will be highly appreciated. Thanks in advance.

Java code:

private static final String SIGNATURE_PREFIX = "sha256=";
private static final String HMAC_SHA_ALGORITHM = "HmacSHA256";
private boolean validateSignature(String signatureHeader, String payload, String encoding, String secretToken)

throws UnsupportedEncodingException {
    if (secretToken == null || secretToken.equals("")) {
        LOG.error("webhookSecret not configured. Skip signature validation");
        return false;
    }

    if (!signatureHeader.startsWith(SIGNATURE_PREFIX)) {
        LOG.errorf("Unsupported webhook signature type: {}", signatureHeader);
        return false;
    }
    byte[] signatureHeaderBytes;
    try {
        signatureHeaderBytes = decodeHex(signatureHeader.substring(SIGNATURE_PREFIX.length()).toCharArray());
    } catch (DecoderException e) {
        LOG.errorf("Invalid signature: {}", signatureHeader);
        return false;
    }
    byte[] expectedSignature = getExpectedSignature(payload.getBytes(encoding == null ? "UTF-8" : encoding), secretToken);
    LOG.info("generated signature: "+ bytesToHex(expectedSignature));
    return MessageDigest.isEqual(signatureHeaderBytes, expectedSignature);
}


private byte[] getExpectedSignature(byte[] payload, String secretToken) {

    SecretKeySpec key = new SecretKeySpec(secretToken.getBytes(), HMAC_SHA_ALGORITHM);
    Mac hmac;
    try {
        hmac = Mac.getInstance(HMAC_SHA_ALGORITHM);
        hmac.init(key);
    } catch (NoSuchAlgorithmException e) {
        throw new IllegalStateException("Hmac SHA must be supported", e);
    } catch (InvalidKeyException e) {
        throw new IllegalStateException("Hmac SHA must be compatible to Hmac SHA Secret Key", e);
    }
    return hmac.doFinal(payload);
}

private static String bytesToHex(byte[] hash) {
    StringBuilder hexString = new StringBuilder(2 * hash.length);
    for (int i = 0; i < hash.length; i++) {
        String hex = Integer.toHexString(0xff & hash[i]);
        if (hex.length() == 1) {
            hexString.append('0');
        }
        hexString.append(hex);
    }
    return hexString.toString();
}


public static byte[] decodeHex(final char[] data) throws DecoderException {
    final byte[] out = new byte[data.length >> 1];
    final int outOffset = 0;
    final int len = data.length;

    if ((len & 0x01) != 0) {
        throw new DecoderException("Odd number of characters.");
    }

    final int outLen = len >> 1;
    if (out.length - outOffset < outLen) {
        throw new DecoderException("Output array is not large enough to accommodate decoded data.");
    }

    // two characters form the hex value.
    for (int i = outOffset, j = 0; j < len; i++) {
        int f = toDigit(data[j], j) << 4;
        j++;
        f = f | toDigit(data[j], j);
        j++;
        out[i] = (byte) (f & 0xFF);
    }

    return out;
}


protected static int toDigit(final char ch, final int index) throws DecoderException {
    final int digit = Character.digit(ch, 16);
    if (digit == -1) {
        throw new DecoderException("Illegal hexadecimal character " + ch + " at index " + index);
    }
    return digit;
}