Fix new Sonar smells

* And more convenient Kotlin methods based on `IntegrationFlow`

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

@@ -258,7 +258,9 @@ public HeaderEnricherSpec headerExpressions(Consumer<StringStringMapBuilder> con
 	 * @param overwrite true to overwrite existing headers.
 	 * @return the header enricher spec.
 	 */
-	public HeaderEnricherSpec headerExpressions(Consumer<StringStringMapBuilder> configurer, Boolean overwrite) {
+	public HeaderEnricherSpec headerExpressions(Consumer<StringStringMapBuilder> configurer,
+			@Nullable Boolean overwrite) {
+
 		Assert.notNull(configurer, "'configurer' must not be null");
 		StringStringMapBuilder builder = new StringStringMapBuilder();
 		configurer.accept(builder);

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/AbstractKotlinRouterSpec.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2023 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.
@@ -49,7 +49,11 @@ abstract class AbstractKotlinRouterSpec<S : AbstractRouterSpec<S, R>, R : Abstra
 	}
 
 	fun defaultSubFlowMapping(subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.defaultSubFlowMapping { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		defaultSubFlowMapping {definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
+	}
+
+	fun defaultSubFlowMapping(subFlow: IntegrationFlow) {
+		this.delegate.defaultSubFlowMapping(subFlow)
 	}
 
 	fun defaultOutputToParentFlow() {

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinEnricherSpec.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2023 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.
@@ -74,7 +74,11 @@ class KotlinEnricherSpec(val delegate: EnricherSpec)
 	}
 
 	fun requestSubFlow(subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.requestSubFlow { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		requestSubFlow {definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
+	}
+
+	fun requestSubFlow(subFlow: IntegrationFlow) {
+		this.delegate.requestSubFlow(subFlow)
 	}
 
 	fun shouldClonePayload(shouldClonePayload: Boolean) {

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinFilterEndpointSpec.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2023 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.
@@ -48,7 +48,11 @@ class KotlinFilterEndpointSpec(val delegate: FilterEndpointSpec)
 	}
 
 	fun discardFlow(subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.discardFlow { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		discardFlow {definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
+	}
+
+	fun discardFlow(subFlow: IntegrationFlow) {
+		this.delegate.discardFlow(subFlow)
 	}
 
 }

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinIntegrationFlowDefinition.kt

@@ -836,7 +836,7 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 		routerConfigurer: KotlinRouterSpec<T, ExpressionEvaluatingRouter>.() -> Unit = {}
 	) {
 
-		this.delegate.route<T>(expression) { routerConfigurer(KotlinRouterSpec(it)) }
+		this.delegate.route(expression) { routerConfigurer(KotlinRouterSpec(it)) }
 	}
 
 	/**

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinRecipientListRouterSpec.kt

@@ -17,8 +17,6 @@
 package org.springframework.integration.dsl
 
 import org.springframework.expression.Expression
-import org.springframework.integration.core.GenericSelector
-import org.springframework.integration.core.MessageSelector
 import org.springframework.integration.router.RecipientListRouter
 import org.springframework.messaging.Message
 import org.springframework.messaging.MessageChannel
@@ -77,15 +75,27 @@ class KotlinRecipientListRouterSpec(override val delegate: RecipientListRouterSp
 	}
 
 	fun recipientFlow(subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.recipientFlow { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		recipientFlow { definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
 	}
 
 	fun recipientFlow(expression: String, subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.recipientFlow(expression) { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		recipientFlow(expression) { definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
 	}
 
 	fun recipientFlow(expression: Expression, subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.recipientFlow(expression) { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		recipientFlow(expression) { definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
+	}
+
+	fun recipientFlow(subFlow: IntegrationFlow) {
+		this.delegate.recipientFlow(subFlow)
+	}
+
+	fun recipientFlow(expression: String, subFlow: IntegrationFlow) {
+		this.delegate.recipientFlow(expression, subFlow)
+	}
+
+	fun recipientFlow(expression: Expression, subFlow: IntegrationFlow) {
+		this.delegate.recipientFlow(expression, subFlow)
 	}
 
 }

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinRouterSpec.kt

@@ -60,7 +60,11 @@ class KotlinRouterSpec<K, R : AbstractMappingMessageRouter>(override val delegat
 	}
 
 	fun subFlowMapping(key: K, subFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.subFlowMapping(key) { subFlow(KotlinIntegrationFlowDefinition(it)) }
+		subFlowMapping(key) { definition -> subFlow(KotlinIntegrationFlowDefinition(definition)) }
+	}
+
+	fun subFlowMapping(key: K, subFlow: IntegrationFlow) {
+		this.delegate.subFlowMapping(key, subFlow)
 	}
 
 }

spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinSplitterEndpointSpec.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2023 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.
@@ -48,7 +48,11 @@ class KotlinSplitterEndpointSpec<H : AbstractMessageSplitter>(val delegate: Spli
 	}
 
 	fun discardFlow(discardFlow: KotlinIntegrationFlowDefinition.() -> Unit) {
-		this.delegate.discardFlow { discardFlow(KotlinIntegrationFlowDefinition(it)) }
+		discardFlow {definition -> discardFlow(KotlinIntegrationFlowDefinition(definition)) }
+	}
+
+	fun discardFlow(discardFlow: IntegrationFlow) {
+		this.delegate.discardFlow(discardFlow)
 	}
 
 }