如何使用Java客户端同时发布MQTT消息？

Question

i am trying to publish MQTT messages concurrently using 5 java client, such that each java client publish 1000 messages on a particular topic concurrently to a MQTT broker(HIVEMQ)

i have opened multiple threads, each threads create a mqtt client and connect to broker using ssl and try to publish 1000 messages concurrently,messages are being sent but all the connections are not getting successful to broker and i keep on getting exception

Client is not connected (32104)
at org.eclipse.paho.client.mqttv3.internal.ExceptionHelper.createMqttException(ExceptionHelper.java:31)
    at org.eclipse.paho.client.mqttv3.internal.ClientComms.sendNoWait(ClientComms.java:199)
    at org.eclipse.paho.client.mqttv3.MqttAsyncClient.publish(MqttAsyncClient.java:1355)
    at org.eclipse.paho.client.mqttv3.MqttClient.publish(MqttClient.java:583)
    at org.eclipse.paho.client.mqttv3.MqttClient.publish(MqttClient.java:575)
    at com.test.MqttPublishSample.publishMessages(MqttPublishSample.java:122)
    at com.test.MqttPublishSample.lambda$start$0(MqttPublishSample.java:74)
    at java.base/java.lang.Thread.run(Thread.java:834)

public class MqttPublishSample {

    public static void main(String... args) throws InterruptedException {

        new MqttPublishSample().start();

    }

  public void start() throws InterruptedException {


        for(int i=0;i<5;i++){

            new Thread(()->{
                MqttClient client = null;
                try {
                    client = obtainConnection();//code to obtain connection using MqttClient
                    publishMessages(client);//code to publish message using simple for loop 

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

            }).start();
        }
    }

public MqttClient obtainConnection() throws MqttException {
        String clientId = "sslTestClient"+ThreadLocalRandom.current().nextInt(0,5);
        MqttClient client = null;
        try {
            client = new MqttClient("ssl://localhost:8883", clientId, new MemoryPersistence());
        } catch (MqttException e) {
            e.printStackTrace();
        }

        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
        mqttConnectOptions.setUserName("user1");
        mqttConnectOptions.setPassword("pass1".toCharArray());
        try {
            mqttConnectOptions.setSocketFactory(getTruststoreFactory());
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println("connecting...");
        client.connect(mqttConnectOptions);
        return client;
    }

i am expecting all clients gets successfully connected to broker and publish message without the exception

Answer 1

It might be that you are using the same clientID over you thread, thus, the server will disconnect duplicate. As you are using LocalThreadRandom, there is a chance of collision (big enough as there are only 5 choices). You might use a unique identifier provided by generateClientId() or share a method between thread that keep trace of them.