Spring DSL defaultOutputToParentFlow does not behave as described

[dobretony]

In what version(s) of Spring Integration are you seeing this issue?
5.1.4.RELEASE

Describe the bug

When creating an IntegrationFlow bean using IntegrationFlows.from(CHANNEL), in the route(Function<S, T> router, Consumer<RouterSpec<T, MethodInvokingRouter>> routerConfigurer) method, when configuring the router mappings, the method defaultOutputToParentFlow() does not what the documentation says it does.

Example:

Given this Integration Flow definition:

 @Bean
    public IntegrationFlow orderIntegrationFlow() {
        return IntegrationFlows.from(CHANNEL)
                .<Order, OrderType>route(Order::getType,
                        r -> r.channelMapping(OrderType.DINE_IN, DineInOrderFlow.CHANNEL)
                                .channelMapping(OrderType.ONLINE, OnlineOrderFlow.CHANNEL)
                                .defaultOutputToParentFlow()
                )
                .log("It only reaches here if Order::getType is null.")
                .get();
    }

The log will only get printed if Order::getType is null. This is contrary to the javadoc which says that:

Make a default output mapping of the router to the parent flow. Use the next, after router, parent flow MessageChannel as a AbstractMessageRouter.setDefaultOutputChannel(MessageChannel) of this router.

To Reproduce

Create a Spring project in Java 11, using Spring 5.3.20 and Spring Integration 5.1.4.RELEASE .

Create an IntegrationFlow bean using the default IntegrationFlows.from() method:

    public static final String CHANNEL = "orderInputChannel";

    @Bean(name = CHANNEL)
    public MessageChannel getChannel() {
        DirectChannel dc = new DirectChannel();
        dc.setComponentName(CHANNEL);
        return dc;
    }


    @Bean
    public IntegrationFlow orderIntegrationFlow() {
        return IntegrationFlows.from(CHANNEL)
                .<Order, OrderType>route(Order::getType,
                        r -> r.channelMapping(OrderType.DINE_IN, DineInOrderFlow.CHANNEL)
                                .channelMapping(OrderType.ONLINE, OnlineOrderFlow.CHANNEL)
                                .defaultOutputToParentFlow()
                )
                .log("It only reaches here if Order::getType is null.")
                .get();
    }

Create a class called Order:

public class Order {

    private OrderType orderType;
    public OrderType getType() {
        return orderType;
    }

    public void setType(OrderType orderType) {
        this.orderType = orderType;
    }

}

And an enum called OrderType:

public enum OrderType {
    DINE_IN,
    ONLINE,
    TAKEAWAY;
}

And with everything setup correctly, send a message to CHANNEL of an Order with OrderType.TAKEAWAY.

Expected behavior

The log() at the end of the orderIntegrationFlow will be called because the defaultOutputToParent reached a default state.

** Actual behavior **

An Exception is thrown where TAKEAWAY is not found to be a proper CHANNEL name defined in the Spring Context. Only if Order::getOrderType returns null, then the log() function is called.

Sample

A link to a GitHub repository with a minimal, reproducible sample.

Reports that include a sample will take priority over reports that do not.
At times, we may require a sample, so it is good to try and include a sample up front.

[garyrussell]

5.1.x is no longer supported: https://spring.io/projects/spring-integration#support

See .noChannelKeyFallback().

	/**
	 * By default, if a resolved channel key does not exist in the channel map, the key
	 * itself is used as the channel name, which we will attempt to resolve to a channel.
	 * Invoke this method to disable this feature. This could be useful to prevent
	 * malicious actors from generating a message that could cause the message to be
	 * routed to an unexpected channel, such as one upstream of the router, which would
	 * cause a stack overflow.
	 * @return the router spec.
	 * @since 5.2
	 */
	public RouterSpec<K, R> noChannelKeyFallback() {
		this.handler.setChannelKeyFallback(false);
		return _this();
	}

[dobretony]

All right, thank you for the information. Sorry to bother with an unsupported version.

[artembilan]

The property for version you use is this:

	/**
	 * @param resolutionRequired the resolutionRequired.
	 * @return the router spec.
	 * @see AbstractMappingMessageRouter#setResolutionRequired(boolean)
	 */
	public RouterSpec<K, R> resolutionRequired(boolean resolutionRequired) {

More JavaDocs are here:

	/**
	 * Specify whether this router should ignore any failure to resolve a channel name to
	 * an actual MessageChannel instance when delegating to the ChannelResolver strategy.
	 * @param resolutionRequired true if resolution is required.
	 */
	public void setResolutionRequired(boolean resolutionRequired) {

And respective docs: https://docs.spring.io/spring-integration/docs/current/reference/html/message-routing.html#router-common-parameters-all.

Since this defaultOutputToParentFlow() is a bit misleading, I believe we can improve end-user experience at least with more JavaDocs on this method.

Reopening...

[garyrussell]

Good point @artembilan I had forgotten about that property; while polishing the javadocs, we should note that noChannelKeyFallback is a little more efficient because it doesn't attempt resolution at all.