提供一个简单的Eclipse Paho MQTT的客户端代码

好的，以下是一个简单的 Eclipse Paho MQTT 客户端代码，用于连接到 MQTT 代理并发布消息：

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

public class MQTTClient {
    public static void main(String[] args) {
        String topic = "test/topic";
        String content = "Hello, World!";
        int qos = 2;
        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);
            System.out.println("Connecting to broker: " + broker);
            mqttClient.connect(connOpts);
            System.out.println("Connected");

            System.out.println("Publishing message: " + content);
            MqttMessage message = new MqttMessage(content.getBytes());
            message.setQos(qos);
            mqttClient.publish(topic, message);
            System.out.println("Message published");

            mqttClient.disconnect();
            System.out.println("Disconnected");
            System.exit(0);
        } 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();
        }
    }
}

这个客户端连接到 Eclipse 的公共 MQTT 测试代理，并发布一条消息到 "test/topic" 主题。你可以根据你的实际需求进行修改。