给我展示Eclipse Paho 提供的 MQTT Java 示例代码

当然，我可以展示Paho MQTT Java的示例代码。下面是使用Eclipse Paho实现MQTT的Java示例代码：

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

public class MqttClientDemo {

public static void main(String[] args) throws MqttException, InterruptedException {

String broker ="tcp://localhost:1883";
String clientId = MqttClient.generateClientId();

MqttClient client = new MqttClient(broker, clientId);
MqttConnectOptions connectOptions = new MqttConnectOptions();

connectOptions.setUserName("username");
connectOptions.setPassword("password".toCharArray());

client.connect(connectOptions);

String topic = "test";
int qos = 1;

client.subscribe(topic, qos);

String content = "Hello MQTT";
MqttMessage message = new MqttMessage(content.getBytes());
message.setQos(qos);
client.publish(topic, message);

Thread.sleep(1000);

client.disconnect();
}
}

我希望这个简单的MQTT示例能够帮助你开始使用Eclipse Paho。