java使用mqtt双向通信代码

Java中使用MQTT实现双向通信的代码如下：

首先，需要引入mqtt-client的依赖包，可以通过Maven或Gradle进行引入。

接下来，创建一个MqttClient对象并连接到MQTT服务器：

String broker = "tcp://localhost:1883";
String clientId = "JavaExample";
MemoryPersistence persistence = new MemoryPersistence();
MqttClient mqttClient = new MqttClient(broker, clientId, persistence);
mqttClient.connect();

然后，创建一个MqttMessage对象并设置消息内容：

String content = "Hello, World!";
MqttMessage message = new MqttMessage(content.getBytes());

接着，创建一个MqttTopic对象并发布消息：

String topicName = "example/topic";
MqttTopic topic = mqttClient.getTopic(topicName);
topic.publish(message);

最后，订阅主题并接收消息：

mqttClient.subscribe(topicName, new MqttCallback() {
    @Override
    public void connectionLost(Throwable throwable) {
        System.out.println("Connection lost!");
    }

    @Override
    public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
        System.out.println("Received message: " + new String(mqttMessage.getPayload()));
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
        System.out.println("Delivery complete!");
    }
});