Binding properties are supplied using the format spring.cloud.stream.bindings.<channelName>.<property>=<value>. The <channelName> represents the name of the channel being configured (e.g., output for a Source).

To avoid repetition, Spring Cloud Stream supports setting values for all channels, in the format spring.cloud.stream.default.<property>=<value>.

In what follows, we indicate where we have omitted the spring.cloud.stream.bindings.<channelName>. prefix and focus just on the property name, with the understanding that the prefix will be included at runtime.

Besides the channels defined via @EnableBinding, Spring Cloud Stream allows applications to send messages to dynamically bound destinations. This is useful, for example, when the target destination needs to be determined at runtime. Applications can do so by using the BinderAwareChannelResolver bean, registered automatically by the @EnableBinding annotation.

The property 'spring.cloud.stream.dynamicDestinations' can be used for restricting the dynamic destination names to a set known beforehand (whitelisting). If the property is not set, any destination can be bound dynamicaly.

The BinderAwareChannelResolver can be used directly as in the following example, in which a REST controller uses a path variable to decide the target channel.

@EnableBinding
@Controller
public class SourceWithDynamicDestination {

	@Autowired
	private BinderAwareChannelResolver resolver;

	@RequestMapping(path = "/{target}", method = POST, consumes = "*/*")
	@ResponseStatus(HttpStatus.ACCEPTED)
	public void handleRequest(@RequestBody String body, @PathVariable("target") target,
	       @RequestHeader(HttpHeaders.CONTENT_TYPE) Object contentType) {
		sendMessage(body, target, contentType);
	}

	private void sendMessage(String body, String target, Object contentType) {
		resolver.resolveDestination(target).send(MessageBuilder.createMessage(body,
				new MessageHeaders(Collections.singletonMap(MessageHeaders.CONTENT_TYPE, contentType))));
	}
}

After starting the application on the default port 8080, when sending the following data:

curl -H "Content-Type: application/json" -X POST -d "customer-1" http://localhost:8080/customers

curl -H "Content-Type: application/json" -X POST -d "order-1" http://localhost:8080/orders

The destinations 'customers' and 'orders' are created in the broker (for example: exchange in case of Rabbit or topic in case of Kafka) with the names 'customers' and 'orders', and the data is published to the appropriate destinations.

The BinderAwareChannelResolver is a general purpose Spring Integration DestinationResolver and can be injected in other components. For example, in a router using a SpEL expression based on the target field of an incoming JSON message.

@EnableBinding
@Controller
public class SourceWithDynamicDestination {

	@Autowired
	private BinderAwareChannelResolver resolver;


	@RequestMapping(path = "/", method = POST, consumes = "application/json")
	@ResponseStatus(HttpStatus.ACCEPTED)
	public void handleRequest(@RequestBody String body, @RequestHeader(HttpHeaders.CONTENT_TYPE) Object contentType) {
		sendMessage(body, contentType);
	}

	private void sendMessage(Object body, Object contentType) {
		routerChannel().send(MessageBuilder.createMessage(body,
				new MessageHeaders(Collections.singletonMap(MessageHeaders.CONTENT_TYPE, contentType))));
	}

	@Bean(name = "routerChannel")
	public MessageChannel routerChannel() {
		return new DirectChannel();
	}

	@Bean
	@ServiceActivator(inputChannel = "routerChannel")
	public ExpressionEvaluatingRouter router() {
        ExpressionEvaluatingRouter router =
            new ExpressionEvaluatingRouter(new SpelExpressionParser().parseExpression("payload.target"));
		router.setDefaultOutputChannelName("default-output");
		router.setChannelResolver(resolver);
		return router;
	}
}