mqtt发送十六进制数据

MQTT协议本身并不支持发送十六进制数据，但是可以将十六进制数据转换为字节数组，然后将字节数组作为payload发送。

下面是一个Java示例代码，将十六进制字符串转换为字节数组，并使用Eclipse Paho MQTT客户端发送：

import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;

public class MqttSendHex {
    public static void main(String[] args) {
        String broker = "tcp://localhost:1883";
        String clientId = "JavaMqttClient";
        String topic = "test/topic";
        String hexString = "DEADBEEF"; // 十六进制字符串
        byte[] payload = hexStringToByteArray(hexString); // 将十六进制字符串转换为字节数组

        try {
            MqttClient client = new MqttClient(broker, clientId);
            MqttConnectOptions options = new MqttConnectOptions();
            options.setCleanSession(true);
            client.connect(options);
            MqttMessage message = new MqttMessage(payload);
            message.setQos(0);
            client.publish(topic, message);
            client.disconnect();
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }

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

这个示例程序将十六进制字符串"DEADBEEF"转换为字节数组，并将字节数组作为消息payload发送到MQTT代理的"test/topic"主题上。请根据实际情况修改broker、clientId、topic等参数。