如何在HiveMQ客戶端中打印所有主題？ （MQTT）

Question

有沒有辦法打印HiveMQ代理存儲的所有主題？ 我想在HiveMQ Client的主類中打印出客戶端連接用於測試目的的所有主題。 我為HiveMQ客戶和社區（經紀人）留下了鏈接。

HiveMQ：

https://github.com/hivemq/hivemq-community-edition https://github.com/hivemq/hivemq-mqtt-client

HiveMQ Client在我的主類中的代碼：

package com.main;

import java.util.UUID;

import com.hivemq.client.mqtt.MqttGlobalPublishFilter;
import com.hivemq.client.mqtt.datatypes.MqttQos;
import com.hivemq.client.mqtt.mqtt5.Mqtt5BlockingClient;
import com.hivemq.client.mqtt.mqtt5.Mqtt5BlockingClient.Mqtt5Publishes;
import com.hivemq.client.mqtt.mqtt5.Mqtt5Client;
import com.hivemq.client.mqtt.mqtt5.message.publish.Mqtt5Publish;
import java.util.logging.Logger;
import java.util.NoSuchElementException;

import java.util.logging.Level;
import java.util.concurrent.TimeUnit;


public class Main {

    private static final Logger LOGGER = Logger.getLogger(Main.class.getName());  // Creates a logger instance 


    public static void main(String[] args) {

                Mqtt5BlockingClient client1 = Mqtt5Client.builder()
            .identifier(UUID.randomUUID().toString()) // the unique identifier of the MQTT client. The ID is randomly generated between 
            .serverHost("localhost")  // the host name or IP address of the MQTT server. Kept it 0.0.0.0 for testing. localhost is default if not specified.
            .serverPort(1883)  // specifies the port of the server
            .buildBlocking();  // creates the client builder

            client1.connect();  // connects the client
            System.out.println("Client1 Connected");
            System.out.println(client1.toString());


            String testmessage = "How is it going!";
            byte[] messagebytesend = testmessage.getBytes();   // stores a message as a byte array to be used in the payload 

    try {  

        Mqtt5Publishes publishes = client1.publishes(MqttGlobalPublishFilter.ALL);  // creates a "publishes" instance thats used to queue incoming messages

            client1.subscribeWith()  // creates a subscription 
            .topicFilter("test1/#")  // filters to receive messages only on this topic (# = Multilevel wild card, + = single level wild card)
            .qos(MqttQos.AT_LEAST_ONCE)  // Sets the QoS to 2 (At least once) 
            .send(); 
            System.out.println("The client1 has subscribed");


            client1.publishWith()  // publishes the message to the subscribed topic 
            .topic("test/pancakes/topic")   // publishes to the specified topic
            .qos(MqttQos.AT_LEAST_ONCE)  
            .payload(messagebytesend)  // the contents of the message 
            .send();
            System.out.println("The client1 has published");


            Mqtt5Publish receivedMessage = publishes.receive(5,TimeUnit.SECONDS).get(); // receives the message using the "publishes" instance waiting up to 5 seconds                                                                          // .get() returns the object if available or throws a NoSuchElementException 


         byte[] tempdata = receivedMessage.getPayloadAsBytes();    // converts the "Optional" type message to a byte array 
         System.out.println();
         String getdata = new String(tempdata); // converts the byte array to a String 
         System.out.println(getdata);


    }

    catch (InterruptedException e) {    // Catches interruptions in the thread 
        LOGGER.log(Level.SEVERE, "The thread was interrupted while waiting for a message to be received", e);
        }

    catch (NoSuchElementException e){
        System.out.println("There are no received messages");   // Handles when a publish instance has no messages 
    }

    client1.disconnect();  
    System.out.println("Client1 Disconnected");

    }

}

Answer 1

有沒有辦法打印HiveMQ代理存儲的所有主題？

否。MQTT中沒有“將代理中所有主題的列表給我”這樣的東西。

您的代碼可以預訂所有“活動”主題，但這意味着您將捕獲所有主題，除非您將代碼運行7/24的時間維持數月或數年。

只需將您的訂閱更改為以下內容：

client1.subscribeWith().topicFilter("#")

現在，您的代碼將獲得發布者要發布到的所有“活動”主題的消息。 請注意，您的代碼每秒可能會收到數千條消息，並且可能許多消息都針對同一主題。 因此，您將需要過濾掉它們。