How to include a varying number of listeners in Spring JMS?

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One way to include a varying number of listeners in Spring JMS is to use the "dynamic" listener approach. This approach allows for listeners to be added or removed at runtime based on configuration or other factors.

To implement this approach, you can define a listener container bean with a fixed number of listeners, and then use a "MessageListenerAdapter" to delegate the actual message handling to a separate bean. Then, you can programmatically register or unregister instances of this message handling bean as necessary.

Here's an example of how this can be done:

@Configuration
public class JMSConfig {

    @Autowired
    private JmsTemplate jmsTemplate;

    @Bean
    public DefaultMessageListenerContainer jmsListenerContainer() {
        DefaultMessageListenerContainer container = new DefaultMessageListenerContainer();
        container.setConnectionFactory(jmsTemplate.getConnectionFactory());
        container.setDestinationName("myQueue");

        // Use a message listener adapter to delegate to a separate bean
        MessageListenerAdapter listenerAdapter = new MessageListenerAdapter();
        listenerAdapter.setDelegate(new MyMessageListener());

        // Set the message listener adapter as the delegate for each listener
        for (int i = 0; i < 10; i++) {
            SimpleMessageListenerContainer listener = new SimpleMessageListenerContainer();
            listener.setConnectionFactory(jmsTemplate.getConnectionFactory());
            listener.setDestinationName("myQueue");
            listener.setMessageListener(listenerAdapter);
            container.addMessageListener(listener);
        }

        return container;
    }

    // ...other beans and configuration...

}

public class MyMessageListener {

    public void onMessage(Message message) {
        // Handle the message...
    }

}

In this example, we define a message listener container with 10 listeners, each of which uses a message listener adapter to delegate to a separate "MyMessageListener" bean. We can add or remove instances of "MyMessageListener" at runtime by programmatically registering or unregistering instances of the bean with the container.