Spring integration gateway "Dispatcher has no subscribers"

Question

I am getting an exception Dispatcher has no subscribers on the outboundChannel and can't figure out why. I am sure its something simple, I have stripped back my code to a very simple sample below:

My context is:

<bean id="requestService"
    class="com.sandpit.RequestService" />

<integration:channel id="inboundChannel" />

<integration:service-activator id="service"
    input-channel="inboundChannel"
    output-channel="outboundChannel"
    ref="requestService"
    method="handleRequest" />

<integration:channel id="outboundChannel" />

<integration:gateway id="gateway"
    service-interface="com.sandpit.Gateway"
    default-request-channel="inboundChannel"
    default-reply-channel="outboundChannel" />

<bean class="com.sandpit.GatewayTester">
    <property name="gateway"
        ref="gateway" />
</bean>

My Java code is:

public interface Gateway {

    String receive();
    void send(String message);
}

public class RequestService {

    public String handleRequest(String request) {

        return "Request received: " + request;
    }
}

public class GatewayTester implements ApplicationListener<ContextRefreshedEvent> {

    private Gateway gateway;

    public void setGateway(Gateway gateway) {

        this.gateway = gateway;
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {

        gateway.send("Hello world!");
        System.out.println("FROM SERVICE: " + gateway.receive());
    }
}

Note: A breakpoint does tell me that the RequestService is actually handling the request.

Answer 1

receive() with no args needs the reply channel to be a PollableChannel See the documentation.

add <queue/> to the outboundChannel.

Alternatively, You could change your gateway method to be String sendAndReceive(String in) and all will work as expected (and you can even remove the outboundChannel altogether).