阿里云物联网调用接口

我使用Java调用阿里云物联网接口发布消息：
setMessageContent(Base64.getEncoder().encodeToString("C9 03 00 73 00 01 65 99".getBytes()))
发出去的指令格式是ascii字符串，我想要发出去的是hex要怎么修改呢？


public static byte[] hexStringToByteArray(String hexString) {
    int len = hexString.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(hexString.charAt(i), 16) << 4)
                             + Character.digit(hexString.charAt(i+1), 16));
    }
    return data;
}



String messageContent = "C9 03 00 73 00 01 65 99";
// 将空格删除
messageContent = messageContent.replace(" ", "");
byte[] messageBytes = hexStringToByteArray(messageContent);