MQTT客户端重新用于发布/订阅

Question

I have an web server which is getting a lot of messages to the same topic and is returning response messages to another topic.

I am currently re-using the same MQTT client instance both for the callback and for sending the response messages by keeping the MQTT client connected all the time.

However, after one cycle of receiving a message and sending a response, I am able to receive another message but cannot send the response - I have to restart the application server.

Is it a good approach to have a single MQTTclient instance? Is it OK to keep it connected all the time? What's the best approach for this kind of requirement?

Here is my code:

public static void registerCallBack(String topicName, String userName,
        String password, String clientId, MqttCallback callback,
        MqttClient client) {
    MqttConnectOptions options = new MqttConnectOptions();
    options.setCleanSession(true);
    options.setKeepAliveInterval(30);
    options.setUserName(userName);
    options.setPassword(password.toCharArray());

    // Connect to Broker
    try {
        options.setSocketFactory(SslUtil.getSocketFactory(
                ManagerProps.MQTT_BROKER_CA_FILE.getValue(), ""));

        client.setCallback(callback);
        client.connect(options);
        client.subscribe(topicName, 0);
        log.info("successfuly registered callback to topic " + topicName);
    } catch (MqttException me) {
        log.error("MqttException, " + me);
    } catch (Exception e) {
        log.error("Exception, " + e);
    }
}

public static String publishMessage(MqttClient client, String message,
        String topic, String userName, String password) {
    MqttConnectOptions options = new MqttConnectOptions();
    options.setCleanSession(true);
    options.setKeepAliveInterval(30);
    options.setUserName(userName);
    options.setPassword(password.toCharArray());

    try {
        MqttMessage msg = new MqttMessage();
        msg.setPayload(message.getBytes());
        client.publish(topic, msg);
    } catch (MqttException e) {
        log.error("MqttException, " + e);
    } catch (Exception e) {
        log.error("Exception, " + e);
    }

    return message;
}

Answer 1

I was seeing something similar, and got this to work:

final CallbackConnection connection = mqtt.callbackConnection();
    connection.listener(new org.fusesource.mqtt.client.Listener() {

        public void onConnected() {
        }
        public void onDisconnected() {
        }
        public void onFailure(Throwable value) {
            value.printStackTrace();
            System.exit(-2);
        }
        public void onPublish(UTF8Buffer topic, Buffer msg, Runnable ack) {
            String body = msg.utf8().toString();
            if( body.startsWith("REPLY: ")) {     
                // Don't reply to your own reply             
                System.out.println("Replied");
                System.out.println("");
            } else {                    
              try{            
              byte[] reply = "REPLY: Hello Back".getBytes();
              connection.publish(destination, reply, QoS.AT_MOST_ONCE, true, null)  ;
              msg.clear();
            }catch (Exception e){
               e.printStackTrace();
            }  
            }
        }
    });