java发送接受16进制mqtt数据

你可以使用 Eclipse Paho MQTT 客户端来发送和接收 16 进制 MQTT 数据。下面是 Java 代码示例：

发送 16 进制 MQTT 数据：

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MqttPublishSample {
    public static void main(String[] args) {
        String topic = "test";
        String content = "68656C6C6F"; // 16 进制表示的 "hello"
        int qos = 1;
        String broker = "tcp://mqtt.eclipse.org:1883";
        String clientId = "JavaSample";
        MemoryPersistence persistence = new MemoryPersistence();

        try {
            MqttClient mqttClient = new MqttClient(broker, clientId, persistence);
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(true);
            mqttClient.connect(connOpts);
            MqttMessage message = new MqttMessage(hexStringToByteArray(content));
            message.setQos(qos);
            mqttClient.publish(topic, message);
            mqttClient.disconnect();
            System.out.println("Message published");
        } catch (MqttException me) {
            System.out.println("reason " + me.getReasonCode());
            System.out.println("msg " + me.getMessage());
            System.out.println("loc " + me.getLocalizedMessage());
            System.out.println("cause " + me.getCause());
            System.out.println("excep " + me);
            me.printStackTrace();
        }
    }

    private 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;
    }
}

接收 16 进制 MQTT 数据：

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MqttSubscribeSample {
    public static void main(String[] args) {
        String topic = "test";
        int qos = 1;
        String broker = "tcp://mqtt.eclipse.org:1883";
        String clientId = "JavaSample";
        MemoryPersistence persistence = new MemoryPersistence();

        try {
            MqttClient mqttClient = new MqttClient(broker, clientId, persistence);
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(true);
            mqttClient.connect(connOpts);
            mqttClient.subscribe(topic, qos, new IMqttMessageListener() {
                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                    System.out.println("Message received: " + byteArrayToHexString(message.getPayload()));
                }
            });
        } catch (MqttException me) {
            System.out.println("reason " + me.getReasonCode());
            System.out.println("msg " + me.getMessage());
            System.out.println("loc " + me.getLocalizedMessage());
            System.out.println("cause " + me.getCause());
            System.out.println("excep " + me);
            me.printStackTrace();
        }
    }

    private static String byteArrayToHexString(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02X", b));
        }
        return sb.toString();
    }
}

在这个例子中，我们使用 Eclipse Paho MQTT 客户端连接到公共的 MQTT 服务器 mqtt.eclipse.org，并在主题 "test" 上发布和订阅 16 进制消息。注意，在发送消息之前，我们使用 `hexStringToByteArray` 方法将 16 进制字符串转换为字节数组，而在接收消息之后，我们使用 `byteArrayToHexString` 方法将字节数组转换回 16 进制字符串。