SHA-256 encryption method

public static String getSHA256Encrypt(String strSrc) {
        MessageDigest md = null;
        String strDes = null;

        byte[] bt = strSrc.getBytes();
        try { 
            md = MessageDigest.getInstance("SHA-256");
            md.update(bt);
            strDes = bytes2Hex(md.digest());
        }
        catch (NoSuchAlgorithmException e) {
            return null;
        }
        return strDes;
    }
    
    public static String bytes2Hex(byte[]bts) {
        StringBuffer des = new StringBuffer();
        String tmp = null;
        for (int i = 0; i < bts.length; i++) {
            tmp = (Integer.toHexString(bts[i] & 0xFF));
            if (tmp.length() == 1) {
                des.append("0");
            }
            des.append(tmp);
        }
        return des.toString();
    }
    
signInfo=getSHA256Encrypt(merNo+gateWayNo+orderNo+orderCurrency+orderAmount+
+cardNo+cardExpireYear+cardExpireMonth+cardSecurityCode+merKey);