How to compose Spring Integration flows via DSL

Question

I'm trying to figure out how to split up spring integration flows into multiple sub flows and compose them together. Ultimately, I'm trying to lay out a pattern in which I can create modules of subflows that can be pieced together for common integration recipes.

This test case represents a minimal example of trying (but failing) to wire together subflows using the DSL IntegrationFlow API:

@RunWith(SpringRunner.class)
@SpringBootTest(classes = { ComposedIntegrationFlowTest.class })
@SpringIntegrationTest
@EnableIntegration
public class ComposedIntegrationFlowTest {

    @Test
    public void test() {
        MessageChannel beginningChannel = MessageChannels.direct("beginning").get();

        IntegrationFlow middleFlow = f -> f
            .transform("From middleFlow: "::concat)
            .transform(String.class, String::toUpperCase);

        IntegrationFlow endFlow = f -> f
            .handle((p, h) -> "From endFlow: " + p);

        StandardIntegrationFlow composedFlow = IntegrationFlows
            .from(beginningChannel)
            .gateway(middleFlow)
            .gateway(endFlow)
            .get();

        composedFlow.start();

        beginningChannel.send(MessageBuilder.withPayload("hello!").build());
    }
}

Trying the above, I get:

org.springframework.messaging.MessageDeliveryException: Dispatcher has no subscribers for channel 'beginning'.; nested exception is org.springframework.integration.MessageDispatchingException: Dispatcher has no subscribers, failedMessage=GenericMessage [payload=hello!, headers={id=2b1de253-a822-42ba-cd85-009b83a644eb, timestamp=1537890950879}], failedMessage=GenericMessage [payload=hello!, headers={id=2b1de253-a822-42ba-cd85-009b83a644eb, timestamp=1537890950879}]

How do I piece together these subflows? Is there a better API for attempting to do this kind of composition? Is this integration test structured correctly?

Answer 1

composedFlow.start();

That's not enough; you need to register dynamic flows with the IntegrationFlowContext so all the supporting beans are registered with the application context.

Answer 2

Autowire IntegrationFlowContext ...

@Autowired
IntegrationFlowContext integrationFlowContext;

Then register your flow... ...

   integrationFlowContext.registration(integrationFlow).register();