Starting with version 4.1, it is possible to programmatically change the topics to which the adapter is subscribed. Methods addTopic() and removeTopic() are provided. When adding topics, you can optionally specify the QoS (default: 1). You can also modify the topics by sending an appropriate message to a <control-bus/> with an appropriate payload: "myMqttAdapter.addTopic('foo', 1)".

Stopping/starting the adapter has no effect on the topic list (it does not revert to the original settings in the configuration). The changes are not retained beyond the life cycle of the application context; a new application context will revert to the configured settings.

Changing the topics while the adapter is stopped (or disconnected from the broker) will take effect the next time a connection is established.

The following Spring Boot application provides an example of configuring the inbound adapter using Java configuration:

@SpringBootApplication
public class MqttJavaApplication {

    public static void main(String[] args) {
    	new SpringApplicationBuilder(MqttJavaApplication.class)
    			.web(false)
    			.run(args);
    }

    @Bean
    public MessageChannel mqttInputChannel() {
    	return new DirectChannel();
    }

    @Bean
    public MessageProducer inbound() {
    	MqttPahoMessageDrivenChannelAdapter adapter =
    			new MqttPahoMessageDrivenChannelAdapter("tcp://localhost:1883", "testClient",
    			                                 "topic1", "topic2");
    	adapter.setCompletionTimeout(5000);
    	adapter.setConverter(new DefaultPahoMessageConverter());
    	adapter.setQos(1);
    	adapter.setOutputChannel(mqttInputChannel());
    	return adapter;
    }

    @Bean
    @ServiceActivator(inputChannel = "mqttInputChannel")
    public MessageHandler handler() {
    	return new MessageHandler() {

    		@Override
    		public void handleMessage(Message<?> message) throws MessagingException {
    			System.out.println(message.getPayload());
    		}

    	};
    }

}

The following Spring Boot application provides an example of configuring the outbound adapter using Java configuration:

@SpringBootApplication
@IntegrationComponentScan
public class MqttJavaApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
        		new SpringApplicationBuilder(MqttJavaApplication.class)
        				.web(false)
        				.run(args);
        MyGateway gateway = context.getBean(MyGateway.class);
        gateway.sendToMqtt("foo");
    }

    @Bean
    public MqttPahoClientFactory mqttClientFactory() {
        DefaultMqttPahoClientFactory factory = new DefaultMqttPahoClientFactory();
        MqttConnectOptions options = new MqttConnectOptions();
        options.setServerURIs(new String[] { "tcp://host1:1883", "tcp://host2:1883" });
        options.setUserName("username");
        options.setPassword("password".toCharArray());
        factory.setConnectionOptions(options);
        return factory;
    }

    @Bean
    @ServiceActivator(inputChannel = "mqttOutboundChannel")
    public MessageHandler mqttOutbound() {
        MqttPahoMessageHandler messageHandler =
                       new MqttPahoMessageHandler("testClient", mqttClientFactory());
        messageHandler.setAsync(true);
        messageHandler.setDefaultTopic("testTopic");
        return messageHandler;
    }

    @Bean
    public MessageChannel mqttOutboundChannel() {
        return new DirectChannel();
    }

    @MessagingGateway(defaultRequestChannel = "mqttOutboundChannel")
    public interface MyGateway {

        void sendToMqtt(String data);

    }

}