public static void main(String[] args) throws UnsupportedEncodingException {

        String s = "ô"; //á à

        byte b[] = s.getBytes("UTF-8");

        StringBuilder sb = new StringBuilder();
        for (byte c : b) {
            sb.append("%");
            sb.append(String.format("%02X", c));
        }

        System.out.println(sb);

    }