mqtt 协议_mqtt host-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_23039605/article/details/144354095

MQTT是什么？

为什么用MQTT？

MQTT是什么？

MQTT是一种轻量级的，基于发布-订阅模式的消息传输协议，广泛用于物联网领域

为什么用MQTT？

轻量级：开销低、报文小

可靠：MQTT支持QoS等级，保证消息传递的可靠性

双向通信：MQTT是基于发布-订阅模式的，MQTT客户端、MQTT broker 可以双向通信

对大规模物联网设备的支持

MQTT的5个概念

MQTT客户端：用了MQTT客户端库的设备或应用都是MQTT客户端

MQTTBroker：用来接收消息、传递消息，也包含连接、订阅等操作

发布-订阅模式：发布者和订阅者之间解耦，发布者和订阅者之间不需要建立直接连接

主题：MQTT使用主题来接收消息和传递消息

QoS：MQTT提供了3种服务质量，

QoS 0：最多交付一次，可能丢失数据

QoS 1：至少交付一次，保证收到消息，但消息可能重复

QoS 2：只交付一次，保证消息既不丢失也不重复

MQTT一般工作流程

客户端通过TCP/IP协议与Broker建立连接，客户端向指定主题发布消息，也可以订阅主题接收消息，Broker接收消息并传递消息

paho mqtt 注意事项

paho mqtt：初次连接失败，无法重连

paho mqtt：断开之后重连，通过设置 automaticReconnect 为 true 实现

paho mqtt: client id 保证唯一性(重复会踢掉前面连接)

paho mqtt: 断开连接后，自动重连成功，订阅者正常接收消息，需要设置 cleanSession 为 false，并且 qos 为 1(保证不丢数据, 但是可能接收到重复数据，需要在业务层保证幂等)

发布消息和订阅消息 Java代码示例

/**
 * 南昌接口mqtt发布消息
 * @author zhaohualei
 * @date 2019/6/10
 */
public class MqttPublisher {

    private static final String HOST = Consts.NANCHANG_MQTT_HOST;
    private static final String USER_NAME = Consts.NANCHANG_MQTT_USER_NAME;
    private static final String PASSWORD = Consts.NANCHANG_MQTT_PASSWORD;

    private static MqttClient mqttClient;

    static {
        init();
    }

    private static void init() {
        connect();
    }

    private static void connect() {
        try {
            mqttClient = new MqttClient(HOST, MqttClient.generateClientId(), new MemoryPersistence());
            mqttClient.connect(getConnectionOptions());
            mqttClient.setCallback(new PublisherCallback());
            if (mqttClient.isConnected()) {
                LogUtils.PUSH.info("mqtt client first connect to proxy server success!");
            } else {
                LogUtils.PUSH.info("mqtt client first connect to proxy server failed!");
            }
        } catch (MqttException e) {
            LogUtils.ERROR.error("Nanchang mqtt client first connect to proxy server failed due to exception:", e);
        }
    }

    private static MqttConnectOptions getConnectionOptions() {
        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
        mqttConnectOptions.setUserName(USER_NAME);
        mqttConnectOptions.setPassword(PASSWORD.toCharArray());
        mqttConnectOptions.setCleanSession(true);
        mqttConnectOptions.setMaxInflight(1000);
        mqttConnectOptions.setAutomaticReconnect(true);
        return mqttConnectOptions;
    }

    public static void publish(String data, String topic, String bikeNo) {
        if (mqttClient.isConnected()) {
            MqttMessage mqttMessage = new MqttMessage();
            mqttMessage.setQos(1);
            mqttMessage.setRetained(false);
            mqttMessage.setPayload(data.getBytes());

            MqttTopic topicObject = mqttClient.getTopic(topic);
            try {
                topicObject.publish(mqttMessage);
                StatisticLogUtil.incr(StatisticAreaNameAndKeyEnum.NANCHANG_BIKE_ORDER.getTotalCountKey());
                StatisticLogUtil.addBikeNumberToRedisSet(StatisticAreaNameAndKeyEnum.NANCHANG_BIKE_ORDER.getSuccessCountKey(), bikeNo);
            } catch (Exception e) {
                LogUtils.ERROR.error("Nanchang mqtt client publish message to topic failed due to exception:", e);
            }
        }
    }

    static class PublisherCallback implements MqttCallbackExtended {

        @Override
        public void connectionLost(Throwable cause) {
            LogUtils.ERROR.error("Nanchang mqtt client connectionLost, cause message:{}", cause.getMessage());
        }

        @Override
        public void messageArrived(String topic, MqttMessage message) throws Exception {
            LogUtils.PUSH.info("Nanchang mqtt client messageArrived，topic:{}, message:{}", topic, new String(message.getPayload()));
        }

        @Override
        public void deliveryComplete(IMqttDeliveryToken token) {
            LogUtils.PUSH.info("Nanchang mqtt client deliveryComplete, isComplete:{}, getException:{}", token.isComplete(), token.getException());
            if (token.isComplete()) {
                if (token.getException() == null) {
                    StatisticLogUtil.incr(StatisticAreaNameAndKeyEnum.NANCHANG_BIKE_ORDER.getSuccessCountKey());
                } else {
                    StatisticLogUtil.incr(StatisticAreaNameAndKeyEnum.NANCHANG_BIKE_ORDER.getFailureCountKey());
                }
            }
        }

        @Override
        public void connectComplete(boolean reconnect, String serverURI) {
            LogUtils.PUSH.info("Nanchang mqtt client connectComplete, reconnect:{}, serverURI:{}", reconnect, serverURI);
        }
    }

}

/**
 * subscribe message.
 * Created by zhaohualei on 2019/01/02.
 */
@Component
public class MqttSubscriber {

    private static final String HOST = Consts.NANCHANG_MQTT_HOST;
    private static final String USER_NAME = Consts.NANCHANG_MQTT_USER_NAME;
    private static final String PASSWORD = Consts.NANCHANG_MQTT_PASSWORD;
    private static final String CLIENT_ID = "client_id";
    private static final String TOPIC_AREA_NOTICE = "monitor/area/notice";
    private static final String TOPIC_STATION_NOTICE = "monitor/station/notice";
    private static final String TOPIC_STAGE_BIKE_INFO = "monitor/stagebike/bikeinfo";
    private static final String TOPIC_AREA_INFO = "monitor/area/information";
    private static final String TOPIC_STATION_INFO = "monitor/station/information";

    @Autowired
    private NanchangSupervisionService nanchangSupervisionService;

    public void subscribe() {
        try {
            MqttClient mqttClient = new MqttClient(HOST, CLIENT_ID, new MemoryPersistence());
            MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
            mqttConnectOptions.setUserName(USER_NAME);
            mqttConnectOptions.setPassword(PASSWORD.toCharArray());
            mqttConnectOptions.setCleanSession(false);
            mqttConnectOptions.setAutomaticReconnect(true);

            mqttClient.connect(mqttConnectOptions);
            if (mqttClient.isConnected()) {
                LogUtils.PUSH.info("mqtt subscribe client first connect to proxy server success!");
            } else {
                LogUtils.PUSH.info("mqtt subscribe client first connect to proxy server failed!");
            }
            mqttClient.subscribe(new String[]{TOPIC_AREA_NOTICE, TOPIC_STATION_NOTICE, TOPIC_STAGE_BIKE_INFO, TOPIC_AREA_INFO, TOPIC_STATION_INFO}, new int[]{1, 1, 1, 1, 1});

            mqttClient.setCallback(new MqttCallbackExtended() {
                @Override
                public void connectionLost(Throwable cause) {
                    LogUtils.ERROR.error("Nanchang mqtt subscribe client connectionLost, cause message:{}", cause.getMessage());
                }

                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                    String payLoad = new String(message.getPayload());
                    LogUtils.PUSH.info("Nanchang mqtt subscribe client messageArrived，topic:{}, message:{}", topic, payLoad);
                    if (StringUtils.isNotBlank(payLoad)) {
                        if (TOPIC_AREA_INFO.equals(topic)) {
                            nanchangSupervisionService.updateAreaInfo(payLoad);
                        } else if (TOPIC_STATION_INFO.equals(topic)) {
                            nanchangSupervisionService.updateStationInfo(payLoad);
                        } else if (TOPIC_AREA_NOTICE.equals(topic)) {
                        } else if (TOPIC_STATION_NOTICE.equals(topic)) {
                        } else if (TOPIC_STAGE_BIKE_INFO.equals(topic)) {
                        }
                    }
                }

                @Override
                public void deliveryComplete(IMqttDeliveryToken token) {
                    LogUtils.PUSH.info("Nanchang mqtt subscribe client deliveryComplete, isComplete:{}, getException:{}", token.isComplete(), token.getException());
                }

                @Override
                public void connectComplete(boolean reconnect, String serverURI) {
                    LogUtils.PUSH.info("Nanchang mqtt subscribe client connectComplete, reconnect:{}, serverURI:{}", reconnect, serverURI);
                }
            });
        } catch (MqttException e) {
            LogUtils.ERROR.error("Nanchang mqtt subscribe client first connect to proxy server failed due to exception:", e);
        }
    }

}