当订阅者在Mqtt主题Java中处于非活动状态时，如何获取生产者发送的所有数据（未保留或最后一条消息）

Question

我一直在寻找整个互联网。 我尝试将cleansession设置为“ false”，并且设置了qos 1和2，但订阅者上线时未获得所有内容。 请帮忙...我的代码是

Example.java（生产者）

public class Example extends PersonBean {
public  void hey(){
String clientId = MqttClient.generateClientId();
 MemoryPersistence persistence = new MemoryPersistence();

    PersonBean pb=new PersonBean();
    for(int i=1;i<=5;i++){
        Gson gson = new Gson();

        Date dt=new Date();
         DateFormat df = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
         String currentTime = df.format(dt);
    pb.setId(i);
    pb.setName("sai");
    pb.setEmail("s@g.com");
    pb.setAddress("hyderabad");
    pb.setCreatedOn(currentTime);


    String jsonInString = gson.toJson(pb);


        try {
            String broker = "tcp://localhost:1883";
            String topicName = "test/mqtt";
            int qos = 2;

    MqttClient mqttClient = new MqttClient(broker,clientId);
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(false);
            mqttClient.connect(connOpts);

            MqttMessage message = new MqttMessage(jsonInString.getBytes());

            message.setQos(qos);
    message.setRetained(true);


            MqttTopic topic2 = mqttClient.getTopic(topicName);
topic2.publish(message);

        mqttClient.disconnect();
        } catch (MqttException me) {
            System.out.println("reason " + me.getReasonCode() + " - msg "
                    + me.getMessage() + "- loc " + me.getLocalizedMessage()
                    + " - cause " + me.getCause() + "- exception " + me);

        }


    }}

    public static void main(String[] args) {
    Example ex=new Example();
    ex.hey();
}}

和我的

Subscriber.java

public class SubcriberExample implements MqttCallback{

MqttClient client;
public void doDemo() {
    try {
        client = new MqttClient("tcp://192.168.4.189:1883", "Sending");
        client.connect();
        client.setCallback(this);
        client.subscribe("test/mqtt");



    } catch (MqttException e) {
        e.printStackTrace();
    }
}

public static void main(String args[]){
    SubcriberExample se=new SubcriberExample();
    se.doDemo();
}

@Override
public void connectionLost(Throwable arg0) {
    // TODO Auto-generated method stub
    System.out.println("connection lost....");
}

@Override
public void deliveryComplete(IMqttDeliveryToken arg0) {
    // TODO Auto-generated method stub

}

@Override
public void messageArrived(String topic, MqttMessage message) throws Exception {
    // TODO Auto-generated method stub
    System.out.println("message is : "+message);
}}

Answer 1

您处在正确的轨道上，发布的消息必须为QoS1 / 2，才有资格保留在脱机队列中（对于脱机订户）。

但是，从上面的代码看来，问题出在订阅者中。 为了使MQTT订阅者能够接收脱机消息，则它需要具有持久会话。 即订户需要使用干净会话= false连接。