请用Java写一个mqtt连接

好的，以下是用Java写一个mqtt连接的示例代码：

import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MqttConnection {
    
    public static void main(String[] args) {
        
        String broker = "tcp://test.mosquitto.org:1883";
        String clientId = "JavaMqttClient";
        MemoryPersistence persistence = new MemoryPersistence();
        
        try {
            MqttClient client = new MqttClient(broker, clientId, persistence);
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(true);
            System.out.println("Connecting to broker: " + broker);
            client.connect(connOpts);
            System.out.println("Successfully connected to broker");
            client.disconnect();
            System.out.println("Disconnected from broker");
            System.exit(0);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

这段代码使用 Eclipse Paho 客户端库来连接 Mosquitto 测试服务器，发送和接收 MQTT 消息需要进一步编码实现。希望这个代码对你有所帮助。