如何从Eclipse Paho中的MQTT读取数据？

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

public class MQTTReader {
    public static void main(String[] args) {
        String broker = "tcp://mqtt.example.com:1883";
        String clientId = "mqtt-reader";
        MemoryPersistence persistence = new MemoryPersistence();

        try {
            MqttClient client = new MqttClient(broker, clientId, persistence);

            MqttCallback callback = new MqttCallback() {
                public void connectionLost(Throwable cause) {
                    // 处理连接丢失的情况
                }

                public void messageArrived(String topic, MqttMessage message) throws Exception {
                    // 处理接收到的消息
                    String payload = new String(message.getPayload());
                    System.out.println("Received message: " + payload);
                }

                public void deliveryComplete(IMqttDeliveryToken token) {
                    // 消息传递完成后的处理
                }
            };

            client.setCallback(callback);
            client.connect();

            String topic = "my/topic";
            int qos = 1;
            client.subscribe(topic, qos);

        } catch (MqttException e) {
            e.printStackTrace();
        }
    }
}