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Detecting Idle Asynchronous Consumers

While efficient, one problem with asynchronous consumers is detecting when they are idle — users might want to take some action if no messages arrive for some period of time.

Starting with version 1.6, it is now possible to configure the listener container to publish a ListenerContainerIdleEvent when some time passes with no message delivery. While the container is idle, an event is published every idleEventInterval milliseconds.

To configure this feature, set idleEventInterval on the container. The following example shows how to do so in XML and in Java (for both a SimpleMessageListenerContainer and a SimpleRabbitListenerContainerFactory):

<rabbit:listener-container connection-factory="connectionFactory"
        ...
        idle-event-interval="60000"
        ...
        >
    <rabbit:listener id="container1" queue-names="foo" ref="myListener" method="handle" />
</rabbit:listener-container>

@Bean
public SimpleMessageListenerContainer(ConnectionFactory connectionFactory) {
    SimpleMessageListenerContainer container = new SimpleMessageListenerContainer(connectionFactory);
    ...
    container.setIdleEventInterval(60000L);
    ...
    return container;
}

@Bean
public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
    SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
    factory.setConnectionFactory(rabbitConnectionFactory());
    factory.setIdleEventInterval(60000L);
    ...
    return factory;
}

In each of these cases, an event is published once per minute while the container is idle.

Event Consumption

You can capture idle events by implementing ApplicationListener — either a general listener, or one narrowed to only receive this specific event. You can also use @EventListener, introduced in Spring Framework 4.2.

The following example combines the @RabbitListener and @EventListener into a single class. You need to understand that the application listener gets events for all containers, so you may need to check the listener ID if you want to take specific action based on which container is idle. You can also use the @EventListener condition for this purpose.

The events have four properties:

source: The listener container instance
id: The listener ID (or container bean name)
idleTime: The time the container had been idle when the event was published
queueNames: The names of the queue(s) that the container listens to

The following example shows how to create listeners by using both the @RabbitListener and the @EventListener annotations:

public class Listener {

    @RabbitListener(id="someId", queues="#{queue.name}")
    public String listen(String foo) {
        return foo.toUpperCase();
    }

    @EventListener(condition = "event.listenerId == 'someId'")
    public void onApplicationEvent(ListenerContainerIdleEvent event) {
        ...
    }

}

Event listeners see events for all containers. Consequently, in the preceding example, we narrow the events received based on the listener ID.

If you wish to use the idle event to stop the lister container, you should not call container.stop() on the thread that calls the listener. Doing so always causes delays and unnecessary log messages. Instead, you should hand off the event to a different thread that can then stop the container.