Adding Dynamically created queues to a listener RabbitMq Spring

Question

I am creating a Web Application for events-planners to better manage their events. Each event they create needs a queue which means the app needs to create a queue when an event is created. So far I have been able to create the queues and they appear in the rabbitmq management console but when I try to add a queue to a listener it brings this error: java.lang.NullPointerException: Cannot invoke "org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.addQueueNames(String[])" because the return value of "co.ke.mpango.backend.config.webSocket.RabbitQueueServiceImpl.getMessageListenerContainerById Here is the code:

@Service
@Log4j2
public class RabbitQueueServiceImpl implements RabbitQueueService
{
    @Autowired
    private RabbitAdmin rabbitAdmin;
    @Autowired
    private RabbitListenerEndpointRegistry rabbitListenerEndpointRegistry;

    @Override
    public void addNewQueue(String queueName, String exchangeName, String routingKey) {
        Queue queue = new Queue(queueName, true, false, false);
        Binding binding = new Binding(
                queueName,
                Binding.DestinationType.QUEUE,
                exchangeName,
                routingKey,
                null
        );
        rabbitAdmin.declareQueue(queue);
        rabbitAdmin.declareBinding(binding);
        this.addQueueToListener(exchangeName,queueName);
    }

    @Override
    public void addQueueToListener(String listenerId, String queueName) {
        log.info("adding queue : " + queueName + " to listener with id : " + listenerId);
        if (!checkQueueExistOnListener(listenerId,queueName)) {
            this.getMessageListenerContainerById(listenerId).addQueueNames(queueName);
            log.info("queue ");
        } else {
            log.info("given queue name : " + queueName + " not exist on given listener id : " + listenerId);
        }
    }

    @Override
    public void removeQueueFromListener(String listenerId, String queueName) {
        log.info("removing queue : " + queueName + " from listener : " + listenerId);
        if (checkQueueExistOnListener(listenerId,queueName)) {
            this.getMessageListenerContainerById(listenerId).removeQueueNames(queueName);
            log.info("deleting queue from rabbit management");
            this.rabbitAdmin.deleteQueue(queueName);
        } else {
            log.info("given queue name : " + queueName + " not exist on given listener id : " + listenerId);
        }
    }

    @Override
    public Boolean checkQueueExistOnListener(String listenerId, String queueName) {
        try {
            log.info("checking queueName : " + queueName + " exist on listener id : " + listenerId);
            log.info("getting queueNames");
            String[] queueNames = this.getMessageListenerContainerById(listenerId).getQueueNames();
            if (queueNames != null) {
                log.info("checking " + queueName + " exist on active queues");
                for (String name : queueNames) {
                    log.info("name : " + name + " with checking name : " + queueName);
                    if (name.equals(queueName)) {
                        log.info("queue name exist on listener, returning true");
                        return Boolean.TRUE;
                    }
                }
                return Boolean.FALSE;
            } else {
                log.info("there is no queue exist on listener");
                return Boolean.FALSE;
            }
        } catch (Exception e) {
            log.error("Error on checking queue exist on listener");
            return Boolean.FALSE;
        }
    }

    private AbstractMessageListenerContainer getMessageListenerContainerById(String listenerId) {
        log.info("getting message listener container by id : " + listenerId);
        return ((AbstractMessageListenerContainer) this.rabbitListenerEndpointRegistry
                .getListenerContainer(listenerId)
        );
    }
}

Added: How could then one listener be defined?

Answer 1

RabbitListenerEndpointRegistry class is storage for all listener containers( SimpleRabbitListenerContainer , DirectRabbitListenerContainer ) and for managing their life cycle. Before taking MessageListenerContainer from RabbitListenerEndpointRegistry you need to register this container inside the registry like this:

SimpleRabbitListenerEndpoint endpoint = new SimpleRabbitListenerEndpoint();
endpoint.setId(LISTENER_CONTAINER_ID);
endpoint.setMessageListener(message -> {
        RabbitMQMessage<QueueItem> rabbitMQMessage = (RabbitMQMessage<QueueItem>) SerializationUtils.deserialize(message.getBody());
        rabbitMQService.onMessage(rabbitMQMessage); //method where your message will be processed
});

//listenerContainerFactory is instance of DirectRabbitListenerContainerFactory or SimpleRabbitListenerContainerFactory
registry.registerListenerContainer(endpoint, listenerContainerFactory, true);

//start the registry if it is created manually
//registry.start();

and then you can take that container from registry by LISTENER_CONTAINER_ID

registry.getListenerContainer(LISTENER_CONTAINER_ID);

To manage dynamic queues it is better to use DirectMessageListenerContainer , this container will open a separate channel for each queue without restarting the container like SimpleRabbitListenerContainer does after adding a new queue and it will take some time until SimpleRabbitListenerContainer will be ready to receive messages from the queues.

See more differences here: https://docs.spring.io/spring-amqp/reference/html/#choose-container