MQTT是一項輕量級的通信協議，用于連接物聯網設備和應用程序。它具有簡單的發布/訂閱模式，可實現基于一定約定的可靠傳輸。MQTT是一種支持多種平臺的協議，可在移動設備和各種計算機系統之間實現高效通信。在物聯網應用程序中，MQTT是一種常見的協議，可用于設備級通信和大規模數據流傳輸。

JAVA是一種十分流行的編程語言，由Sun Microsystems推出。它是一種面向對象的編程語言，具有內存管理功能，常用于開發Web應用程序和企業級應用程序。在這些應用程序中，JAVA提供了豐富的API、框架和庫，可用于實現不同類型的應用。JAVA還具有跨平臺特性，可在多種操作系統和硬件上運行。

// JAVA代碼示例
import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
public class MqttClientDemo {
public static void main(String[] args) {
String broker = "tcp://localhost:1883";
String clientId = "JavaExample";
MemoryPersistence persistence = new MemoryPersistence();
try {
MqttClient mqttClient = new MqttClient(broker, clientId, persistence);
MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
mqttConnectOptions.setCleanSession(true);
System.out.println("Connecting to broker: " + broker);
mqttClient.connect(mqttConnectOptions);
System.out.println("Connected...");
String topic = "mytopic";
System.out.println("Subscribing to topic: " + topic);
mqttClient.subscribe(topic);
System.out.println("Subscribed...");
mqttClient.setCallback(new MqttCallback() {
public void messageArrived(String topic, MqttMessage message) throws Exception {
String payload = new String(message.getPayload());
System.out.println("Message received: " + payload);
}
public void deliveryComplete(IMqttDeliveryToken token) {
}
public void connectionLost(Throwable throwable) {
System.out.println("Connection lost...");
throwable.printStackTrace();
}
});
System.out.println("Listening...");
while (true) {
Thread.sleep(1000);
}
} catch (MqttException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}