脱机消息不在带有Paho客户端的Moquette中使用

Question

我在通过eclipse Paho客户机使用Moquette服务器中的脱机MQTT消息方面遇到了一个问题。

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以上步骤都是成功的，没有任何问题。

然后我停止了我的使用者应用程序，并用相同的主题将MQTT数据发送给broker。使用我的publisher Application-Server能够接收这些消息，但是在这个时刻没有任何使用者来使用此消息，因为我已经停止了我的使用者。然后我再次启动了我的消费者应用程序。它成功地连接到代理，但是，当使用者关闭时，它没有收到我发送给代理的任何消息。

我是否需要对我的Moquette服务器进行任何特定的配置来持久化数据（使用干净的会话：false）？还是我漏掉了什么？

package com.gbids.mqtt.moquette.main;

import com.gbids.mqtt.moquette.server.PublishInterceptor;
import io.moquette.interception.InterceptHandler;
import io.moquette.server.Server;
import io.moquette.server.config.IConfig;
import io.moquette.server.config.MemoryConfig;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.Properties;

public class ServerLauncher {

    public static void main(String[] args) throws IOException {
        Properties props = new Properties();
        final IConfig configs = new MemoryConfig(props);

        final Server mqttBroker = new Server();
        final List<? extends InterceptHandler> userHandlers = Arrays.asList(new PublishInterceptor());
        mqttBroker.startServer(configs, userHandlers);

        System.out.println("moquette mqtt broker started, press ctrl-c to shutdown..");
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                System.out.println("stopping moquette mqtt broker..");
                mqttBroker.stopServer();
                System.out.println("moquette mqtt broker stopped");
            }
        });
    }
}

package com.gbids.mqtt.moquette.main;

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

public class ConsumerLauncher implements MqttCallback {

    private static final String topicPrefix = "devices/reported";
    private static final String broker = "tcp://0.0.0.0:1883";
    private static final String clientIdPrefix = "consumer";

    public static void main(String[] args) throws MqttException {
        final String clientId = "consumer_1";
        MqttClient sampleClient = new MqttClient(broker, clientId, new MemoryPersistence());
        MqttConnectOptions connOpts = new MqttConnectOptions();
        connOpts.setCleanSession(false);
        sampleClient.connect(connOpts);
        sampleClient.subscribe(topicPrefix + "/#", 1);
        sampleClient.setCallback(new ConsumerLauncher());
    }

    public void connectionLost(Throwable throwable) {
        System.out.println("Consumer connection lost : " + throwable.getMessage());
    }

    public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
        System.out.println("Message arrived from topic : " + s + " | Message : " + new String(mqttMessage.getPayload()) + " | Message ID : " +mqttMessage.getId());
    }

    public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
        System.out.println("Delivery completed from : " + clientIdPrefix + "_1");
    }
}

package com.gbids.mqtt.moquette.main;

import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class ClientLauncher {

    private static final String content = "{\"randomData\": 25}";
    private static final String willContent = "Client disconnected unexpectedly";
    private static final String broker = "tcp://0.0.0.0:1883";
    private static final String clientIdPrefix = "client";

    public static void main(String[] args) throws Exception{
        sendDataWithQOSOne();
        System.exit(0);
    }

    private static void sendDataWithQOSOne(){
        try {
            final String clientId = "client_1";
            MqttClient sampleClient = new MqttClient(broker, clientId, new MemoryPersistence());
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(false); // for publisher - this is not needed I think
            sampleClient.connect(connOpts);
            MqttMessage message = new MqttMessage(content.getBytes());
            message.setQos(1);
            final String topic = "devices/reported/" + clientId;
            sampleClient.publish(topic, message);
            System.out.println("Message published from : " + clientId + " with payload of : " + content);
            sampleClient.disconnect();
        } catch (MqttException me) {
            me.printStackTrace();
        }
    }
}

Answer 1

在您的例子中，在ClientLauncher(publisher)中创建MQTTMessage时，需要将Request标志设置为True。默认值为false，如文档中所示。

...    
message.setRetained(true)
...

设置此标志可以将消息保留在代理上并发送到新连接的客户端。请注意，代理只保留一个主题的最后一条消息。没有办法为一个特定的主题保留一个以上的消息。