Question

我们决定在我们的移动应用程序中使用mqtt协议进行聊天模块。我想在服务器端保存主题的消息。但是我看到，mqtt客户端在这里是全局的，所以一种方法是我必须为所有主题订阅mqtt客户端的单个实例并将消息保存在数据库中。但是做到这一点是正确的方法。我只是担心它。

private void buildClient(){
        log.debug("Connecting... "+CLIENT_ID);
        try {
            mqttClient = new MqttClient(envConfiguration.getBrokerUrl(), CLIENT_ID);
        } catch (MqttException e) {
            log.debug("build client stopped due to "+e.getCause());
        }
        chatCallback = new ChatCallback();
        mqttClient.setCallback(chatCallback);
        mqttConnectOptions = new MqttConnectOptions();
        mqttConnectOptions.setCleanSession(false);
    }

    @Override
    public void connect() {
        if(mqttClient == null || !mqttClient.getClientId().equals(CLIENT_ID)){
            buildClient();
        }
        boolean tryConnecting = true;
        while(tryConnecting){
            try {
                mqttClient.connect(mqttConnectOptions);
            } catch (Exception e) {
                log.debug("connection attempt failed "+ e.getCause() + " trying...");
            }
            if(mqttClient.isConnected()){
                tryConnecting = false;
            }else{
                pause();
            }
        }
    }


    @Override
    public void publish() {
        boolean publishCallCompletedErrorFree = false;
        while (!publishCallCompletedErrorFree) {
            try {
                mqttClient.publish(TOPIC, "hello".getBytes(), 1, true);
                publishCallCompletedErrorFree = true;
            } catch (Exception e) {
                log.debug("error occured while publishing "+e.getCause());
            }finally{
                pause();
            }
        }   
    }

    @Override
    public void subscribe() {
        if(mqttClient != null && mqttClient.isConnected()){
            try {
                mqttClient.subscribe(TOPIC, 2);
            } catch (MqttException e) {
                log.debug("subscribing error.."+e.getCause());
            }
        }

    }

    @Override
    public void disconnect() {
        System.out.println(this.mqttClient.isConnected());
        try {
            mqttClient.disconnect();
            log.debug("disconnected..");
        } catch (MqttException e) {
            log.debug("erro occured while disconneting.."+e.getCause());
        }
    }

Answer 1

如何解决此问题有两种可能性：

使用通配符（MQTT中的＃）编写订阅所有主题的MQTT客户端
编写一个代理插件，为您完成工作，具体取决于您使用的经纪人实施

有一个很好的描述如何在HiveMQ website实现这两个选项，也描述了第一个选项的限制。

Mqtt：服务器端的持久消息

1 个答案: