GH-3592: Scatter-Gather: applySeq=true by default

Fixes https://github.com/spring-projects/spring-integration/issues/3592

* Configure XML parser & Java DSL for Scatter-Gather, based on the
`RecipientListRouter` to set an `applySequence` to `true` by default.
This will make a `gatherer` part to fully rely on the default correlation
strategies

spring-integration-core/src/main/java/org/springframework/integration/config/xml/ScatterGatherParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2020 the original author or authors.
+ * Copyright 2014-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -89,7 +89,7 @@ public class ScatterGatherParser extends AbstractConsumerEndpointParser {
 			builder.addConstructorArgReference(scatterChannel);
 		}
 		else {
-			BeanDefinition scattererDefinition = null;
+			BeanDefinition scattererDefinition;
 			if (!hasScatterer) {
 				scattererDefinition = new RootBeanDefinition(RecipientListRouter.class);
 			}
@@ -103,6 +103,11 @@ public class ScatterGatherParser extends AbstractConsumerEndpointParser {
 			if (hasScatterer && scatterer.hasAttribute(ID_ATTRIBUTE)) {
 				scattererId = scatterer.getAttribute(ID_ATTRIBUTE);
 			}
+
+			if (!scatterer.hasAttribute("apply-sequence")) {
+				scattererDefinition.getPropertyValues().addPropertyValue("applySequence", true);
+			}
+
 			parserContext.getRegistry().registerBeanDefinition(scattererId, scattererDefinition); // NOSONAR not null
 			builder.addConstructorArgValue(new RuntimeBeanReference(scattererId));
 		}
@@ -113,7 +118,7 @@ public class ScatterGatherParser extends AbstractConsumerEndpointParser {
 
 		Element gatherer = DomUtils.getChildElementByTagName(element, "gatherer");
 
-		BeanDefinition gathererDefinition = null;
+		BeanDefinition gathererDefinition;
 		if (gatherer == null) {
 			try {
 				gatherer = DOCUMENT_BUILDER_FACTORY.newDocumentBuilder().newDocument().createElement("aggregator");
@@ -125,7 +130,7 @@ public class ScatterGatherParser extends AbstractConsumerEndpointParser {
 		}
 		gathererDefinition = GATHERER_PARSER.parse(gatherer, // NOSONAR
 				new ParserContext(parserContext.getReaderContext(),
-				parserContext.getDelegate(), scatterGatherDefinition));
+						parserContext.getDelegate(), scatterGatherDefinition));
 		String gathererId = id + ".gatherer";
 		if (gatherer != null && gatherer.hasAttribute(ID_ATTRIBUTE)) {
 			gathererId = gatherer.getAttribute(ID_ATTRIBUTE);

spring-integration-core/src/main/java/org/springframework/integration/dsl/BaseIntegrationFlowDefinition.java

@@ -2749,6 +2749,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * Populate a {@link ScatterGatherHandler} to the current integration flow position
 	 * based on the provided {@link RecipientListRouterSpec} for scattering function
 	 * and {@link AggregatorSpec} for gathering function.
+	 * For convenience, the {@link RecipientListRouterSpec#applySequence(boolean)} is set to true by default.
 	 * @param scatterer the {@link Consumer} for {@link RecipientListRouterSpec} to configure scatterer.
 	 * @param gatherer the {@link Consumer} for {@link AggregatorSpec} to configure gatherer.
 	 * @param scatterGather the {@link Consumer} for {@link ScatterGatherSpec} to configure
@@ -2760,6 +2761,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 
 		Assert.notNull(scatterer, "'scatterer' must not be null");
 		RecipientListRouterSpec recipientListRouterSpec = new RecipientListRouterSpec();
+		recipientListRouterSpec.applySequence(true);
 		scatterer.accept(recipientListRouterSpec);
 		AggregatorSpec aggregatorSpec = new AggregatorSpec();
 		if (gatherer != null) {

spring-integration-core/src/test/java/org/springframework/integration/dsl/routers/RouterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -857,7 +857,6 @@ public class RouterTests {
 		public IntegrationFlow scatterGatherFlow() {
 			return f -> f
 					.scatterGather(scatterer -> scatterer
-									.applySequence(true)
 									.recipientFlow(m -> true, sf -> sf.handle((p, h) -> Math.random() * 10))
 									.recipientFlow(m -> true, sf -> sf.handle((p, h) -> Math.random() * 10))
 									.recipientFlow(m -> true, sf -> sf.handle((p, h) -> Math.random() * 10)),
@@ -878,8 +877,7 @@ public class RouterTests {
 					.scatterGather(
 							scatterer -> scatterer
 									.recipientFlow(f1 -> f1.handle((p, h) -> p + " - flow 1"))
-									.recipientFlow(f2 -> f2.handle((p, h) -> p + " - flow 2"))
-									.applySequence(true),
+									.recipientFlow(f2 -> f2.handle((p, h) -> p + " - flow 2")),
 							gatherer -> gatherer
 									.outputProcessor(mg -> mg
 											.getMessages()
@@ -900,7 +898,6 @@ public class RouterTests {
 			return f -> f
 					.scatterGather(
 							scatterer -> scatterer
-									.applySequence(true)
 									.recipientFlow(f1 -> f1.transform(p -> "Sub-flow#1"))
 									.recipientFlow(f2 -> f2
 											.channel(c -> c.executor(taskExecutor))
@@ -923,7 +920,6 @@ public class RouterTests {
 		public IntegrationFlow propagateErrorFromGatherer(TaskExecutor taskExecutor) {
 			return IntegrationFlows.from(Function.class)
 					.scatterGather(s -> s
-									.applySequence(true)
 									.recipientFlow(subFlow -> subFlow
 											.channel(c -> c.executor(taskExecutor))
 											.transform(p -> "foo")),
@@ -943,9 +939,9 @@ public class RouterTests {
 
 		@Bean
 		public IntegrationFlow scatterGatherInSubFlow() {
-			return flow -> flow.scatterGather(s -> s.applySequence(true)
+			return flow -> flow.scatterGather(s -> s
 							.recipientFlow(inflow -> inflow.wireTap(scatterGatherWireTapChannel())
-									.scatterGather(s1 -> s1.applySequence(true)
+									.scatterGather(s1 -> s1
 													.recipientFlow(IntegrationFlowDefinition::bridge)
 													.recipientFlow("sequencetest"::equals,
 															IntegrationFlowDefinition::bridge),

spring-integration-core/src/test/java/org/springframework/integration/scattergather/config/ScatterGatherParserTests-context.xml

@@ -14,7 +14,7 @@
 	<bean id="messageStore" class="org.springframework.integration.store.SimpleMessageStore"/>
 
 	<int:scatter-gather id="scatterGather2" input-channel="input2" gather-channel="gatherChannel" gather-timeout="100">
-		<int:scatterer id="myScatterer" apply-sequence="true">
+		<int:scatterer id="myScatterer">
 			<int:recipient channel="distributionChannel"/>
 		</int:scatterer>
 		<int:gatherer id="myGatherer" message-store="messageStore"/>

spring-integration-core/src/test/java/org/springframework/integration/scattergather/config/ScatterGatherTests-context.xml

@@ -30,7 +30,7 @@
 
 	<!--Distribution scenario-->
 	<scatter-gather input-channel="inputDistribution" output-channel="output" gather-channel="gatherChannel">
-		<scatterer apply-sequence="true">
+		<scatterer>
 			<recipient channel="distribution1Channel"/>
 			<recipient channel="distribution2Channel"/>
 			<recipient channel="distribution3Channel"/>