For the latest stable version, please use Spring Integration 6.4.1!

Operator gateway()

The gateway() operator in an IntegrationFlow definition is a special service activator implementation, to call some other endpoint or integration flow via its input channel and wait for reply. Technically it plays the same role as a nested <gateway> component in a <chain> definition (see Calling a Chain from within a Chain) and allows a flow to be cleaner and more straightforward. Logically, and from business perspective, it is a messaging gateway to allow the distribution and reuse of functionality between different parts of the target integration solution (see Messaging Gateways). This operator has several overloads for different goals:

  • gateway(String requestChannel) to send a message to some endpoint’s input channel by its name;

  • gateway(MessageChannel requestChannel) to send a message to some endpoint’s input channel by its direct injection;

  • gateway(IntegrationFlow flow) to send a message to the input channel of the provided IntegrationFlow.

All of these have a variant with the second Consumer<GatewayEndpointSpec> argument to configure the target GatewayMessageHandler and respective AbstractEndpoint. Also, the IntegrationFlow-based methods allows calling existing IntegrationFlow bean or declare the flow as a sub-flow via an in-place lambda for an IntegrationFlow functional interface or have it extracted in a private method cleaner code style:

@Bean
IntegrationFlow someFlow() {
        return IntegrationFlow
                .from(...)
                .gateway(subFlow())
                .handle(...)
                .get();
}

private static IntegrationFlow subFlow() {
        return f -> f
                .scatterGather(s -> s.recipientFlow(...),
                        g -> g.outputProcessor(MessageGroup::getOne))
}
If the downstream flow does not always return a reply, you should set the requestTimeout to 0 to prevent hanging the calling thread indefinitely. In that case, the flow will end at that point and the thread released for further work.