* Rename TransformerSpec -> TransformerEndpointSpec for better context

meaning of the class
* Introduce `KotlinTransformerEndpointSpec` as an extension of the `TransformerEndpointSpec`
to have an `inline fun <reified P> transformer(crossinline function: (P) -> Any)`
for Kotlin style
* Add `KotlinIntegrationFlowDefinition.transformWith(KotlinTransformerEndpointSpec)`
* Deprecate Kotlin methods which are covered by the mentioned `transformWith()`
* Fix tests to use new API
* Mentioned the change in the doc

Author: artembilan

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

@@ -781,13 +781,13 @@ public <P, T> B transform(@Nullable Class<P> expectedType, GenericTransformer<P,
 	}
 
 	/**
-	 * Populate a {@link MessageTransformingHandler} into the endpoint with provided {@link TransformerSpec} options.
+	 * Populate a {@link MessageTransformingHandler} into the endpoint with provided {@link TransformerEndpointSpec} options.
 	 * One of the 'expression', 'ref', 'refName', 'processor' or 'function' must be provided.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @since 6.2
 	 */
-	public B transformWith(Consumer<TransformerSpec> transformerConfigurer) {
-		return register(new TransformerSpec(), transformerConfigurer);
+	public B transformWith(Consumer<TransformerEndpointSpec> transformerConfigurer) {
+		return register(new TransformerEndpointSpec(), transformerConfigurer);
 	}
 
 	/**

spring-integration-core/src/main/java/org/springframework/integration/dsl/TransformerSpec.java renamed to spring-integration-core/src/main/java/org/springframework/integration/dsl/TransformerEndpointSpec.java

@@ -41,7 +41,7 @@
  *
  * @since 6.2
  */
-public class TransformerSpec extends ConsumerEndpointSpec<TransformerSpec, MessageTransformingHandler> {
+public class TransformerEndpointSpec extends ConsumerEndpointSpec<TransformerEndpointSpec, MessageTransformingHandler> {
 
 	private final AtomicBoolean transformerSet = new AtomicBoolean();
 
@@ -61,7 +61,7 @@ public class TransformerSpec extends ConsumerEndpointSpec<TransformerSpec, Messa
 
 	private MessageProcessorSpec<?> processor;
 
-	protected TransformerSpec() {
+	protected TransformerEndpointSpec() {
 		super(new MessageTransformingHandler());
 	}
 
@@ -70,7 +70,7 @@ protected TransformerSpec() {
 	 * @param expression the SpEL expression to use.
 	 * @return the TransformerSpec
 	 */
-	public TransformerSpec expression(String expression) {
+	public TransformerEndpointSpec expression(String expression) {
 		return expression(PARSER.parseExpression(expression));
 	}
 
@@ -79,7 +79,7 @@ public TransformerSpec expression(String expression) {
 	 * @param expression the SpEL expression to use.
 	 * @return the TransformerSpec
 	 */
-	public TransformerSpec expression(Expression expression) {
+	public TransformerEndpointSpec expression(Expression expression) {
 		assertTransformerSet();
 		this.expression = expression;
 		return this;
@@ -90,19 +90,19 @@ public TransformerSpec expression(Expression expression) {
 	 * @param ref the service to call as a transformer POJO.
 	 * @return the TransformerSpec
 	 */
-	public TransformerSpec ref(Object ref) {
+	public TransformerEndpointSpec ref(Object ref) {
 		assertTransformerSet();
 		this.ref = ref;
 		return this;
 	}
 
 	/**
 	 * Provide a bean name to use a {@link MethodInvokingTransformer}
-	 * (based on {@link BeanNameMessageProcessor})for the target handler.
+	 * (based on {@link BeanNameMessageProcessor}) for the target handler.
 	 * @param refName the bean name for service to call as a transformer POJO.
 	 * @return the TransformerSpec
 	 */
-	public TransformerSpec refName(String refName) {
+	public TransformerEndpointSpec refName(String refName) {
 		assertTransformerSet();
 		this.refName = refName;
 		return this;
@@ -114,7 +114,7 @@ public TransformerSpec refName(String refName) {
 	 * @param method the service method name to call.
 	 * @return the TransformerSpec
 	 */
-	public TransformerSpec method(@Nullable String method) {
+	public TransformerEndpointSpec method(@Nullable String method) {
 		this.method = method;
 		return this;
 	}
@@ -126,7 +126,7 @@ public TransformerSpec method(@Nullable String method) {
 	 * @param <T> the output type.
 	 * @return the TransformerSpec
 	 */
-	public <P, T> TransformerSpec transformer(GenericTransformer<P, T> transformer) {
+	public <P, T> TransformerEndpointSpec transformer(GenericTransformer<P, T> transformer) {
 		assertTransformerSet();
 		this.transformer = transformer;
 		return this;
@@ -140,7 +140,7 @@ public <P, T> TransformerSpec transformer(GenericTransformer<P, T> transformer)
 	 * @param <P> the type ot expect.
 	 * @return the spec.
 	 */
-	public <P> TransformerSpec expectedType(@Nullable Class<P> expectedType) {
+	public <P> TransformerEndpointSpec expectedType(@Nullable Class<P> expectedType) {
 		this.expectedType = expectedType;
 		return this;
 	}
@@ -150,7 +150,7 @@ public <P> TransformerSpec expectedType(@Nullable Class<P> expectedType) {
 	 * @param processor the {@link MessageProcessorSpec} to use.
 	 * @return the TransformerSpec
 	 */
-	public TransformerSpec processor(MessageProcessorSpec<?> processor) {
+	public TransformerEndpointSpec processor(MessageProcessorSpec<?> processor) {
 		assertTransformerSet();
 		this.processor = processor;
 		return this;

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

@@ -92,10 +92,16 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 	}
 
 	/**
-	 * Inline function for [IntegrationFlowDefinition.transform] providing a `transform<MyTypeIn, MyTypeOut>()` variant
+	 * Inline function for [IntegrationFlowDefinition.transform] providing a `transform<MyTypeIn>()` variant
 	 * with reified generic type.
 	 */
-	@Suppress("DEPRECATION")
+	@Deprecated("since 6.2",
+			ReplaceWith("""
+				transformWith { 
+					transformer<Type> { }
+					id("value")
+				}"""))
+	@Suppress("DEPRECATION", "REMOVAL")
 	inline fun <reified P> transform(
 		crossinline function: (P) -> Any,
 		crossinline configurer: GenericEndpointSpec<MessageTransformingHandler>.() -> Unit
@@ -104,6 +110,16 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 		this.delegate.transform(P::class.java, { function(it) }) { configurer(it) }
 	}
 
+	/**
+	 * Inline function for [IntegrationFlowDefinition.transformWith]
+	 * providing a `transform<MyTypeIn>()` variant
+	 * with reified generic type.
+	 * @since 6.2
+	 */
+	fun transformWith(configurer: KotlinTransformerEndpointSpec.() -> Unit) {
+		this.delegate.register(KotlinTransformerEndpointSpec(), configurer)
+	}
+
 	/**
 	 * Inline function for [IntegrationFlowDefinition.split] providing a `split<MyTypeIn>()` variant
 	 * with reified generic type.
@@ -306,7 +322,13 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 	 * for the provided `Transformer` instance.
 	 * @since 5.3.1
 	 */
-	@Suppress("DEPRECATION")
+	@Deprecated("since 6.2",
+			ReplaceWith("""
+				transformWith { 
+					transformer(transformer)
+					id("value")
+				}"""))
+	@Suppress("DEPRECATION", "REMOVAL")
 	fun transform(
 		transformer: Transformer,
 		endpointConfigurer: GenericEndpointSpec<MessageTransformingHandler>.() -> Unit = {}
@@ -315,11 +337,26 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 		this.delegate.transform(transformer) { endpointConfigurer(it) }
 	}
 
+	/**
+	 * Populate the [Transformer] EI Pattern specific [MessageHandler] implementation
+	 * for the provided [Transformer] instance.
+	 * @since 6.2
+	 */
+	fun transform(transformer: Transformer) {
+		this.delegate.transform(transformer)
+	}
+
 	/**
 	 * Populate the [Transformer] EI Pattern specific [MessageHandler] implementation
 	 * for the SpEL [Expression].
 	 */
-	@Suppress("DEPRECATION")
+	@Deprecated("since 6.2",
+			ReplaceWith("""
+				transformWith { 
+					expression("value")
+					id("value")
+				}"""))
+	@Suppress("DEPRECATION", "REMOVAL")
 	fun transform(
 		expression: String,
 		endpointConfigurer: GenericEndpointSpec<MessageTransformingHandler>.() -> Unit = {}
@@ -328,6 +365,16 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 		this.delegate.transform(expression, endpointConfigurer)
 	}
 
+
+	/**
+	 * Populate the [Transformer] EI Pattern specific [MessageHandler] implementation
+	 * for the SpEL [Expression].
+	 * @since 6.2
+	 */
+	fun transform(expression: String) {
+		this.delegate.transform(expression)
+	}
+
 	/**
 	 * Populate the [MessageTransformingHandler] for the [MethodInvokingTransformer]
 	 * to invoke the service method at runtime.
@@ -340,7 +387,14 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 	 * Populate the [MessageTransformingHandler] for the [MethodInvokingTransformer]
 	 * to invoke the service method at runtime.
 	 */
-	@Suppress("DEPRECATION")
+	@Deprecated("since 6.2",
+			ReplaceWith("""
+				transformWith { 
+					ref("value")
+					method("value")
+					id("value")
+				}"""))
+	@Suppress("DEPRECATION", "REMOVAL")
 	fun transform(
 		service: Any, methodName: String?,
 		endpointConfigurer: GenericEndpointSpec<MessageTransformingHandler>.() -> Unit
@@ -354,7 +408,13 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 	 * [org.springframework.integration.handler.MessageProcessor] from provided [MessageProcessorSpec].
 	 * In addition, accept options for the integration endpoint using [GenericEndpointSpec].
 	 */
-	@Suppress("DEPRECATION")
+	@Deprecated("since 6.2",
+			ReplaceWith("""
+				transformWith { 
+					processor("value")
+					id("value")
+				}"""))
+	@Suppress("DEPRECATION", "REMOVAL")
 	fun transform(
 		messageProcessorSpec: MessageProcessorSpec<*>,
 		endpointConfigurer: GenericEndpointSpec<MessageTransformingHandler>.() -> Unit = {}
@@ -363,6 +423,15 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 		this.delegate.transform(messageProcessorSpec, endpointConfigurer)
 	}
 
+	/**
+	 * Populate the [MessageTransformingHandler] instance for the
+	 * [org.springframework.integration.handler.MessageProcessor] from provided [MessageProcessorSpec].
+	 * @since 6.2
+	 */
+	fun transform(messageProcessorSpec: MessageProcessorSpec<*>) {
+		this.delegate.transform(messageProcessorSpec)
+	}
+
 	/**
 	 * Populate a [MessageFilter] with [MessageSelector] for the provided SpEL expression.
 	 * In addition, accept options for the integration endpoint using [KotlinFilterEndpointSpec]:
@@ -571,7 +640,7 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 				delay { 
 					messageGroupId(groupId) 
 				}"""))
-	@Suppress("DEPRECATION")
+	@Suppress("DEPRECATION", "REMOVAL")
 	fun delay(groupId: String, endpointConfigurer: DelayerEndpointSpec.() -> Unit = {}) {
 		this.delegate.delay(groupId, endpointConfigurer)
 	}

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

@@ -0,0 +1,42 @@
+/*
+ * Copyright 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.dsl
+
+import org.springframework.integration.transformer.MessageTransformingHandler
+
+/**
+ * A [TransformerEndpointSpec] wrapped for Kotlin DSL.
+ *
+ * @property delegate the [TransformerEndpointSpec] this instance is delegating to.
+ *
+ * @author Artem Bilan
+ *
+ * @since 6.2
+ */
+class KotlinTransformerEndpointSpec : TransformerEndpointSpec() {
+
+	/**
+	 * Provide a Kotlin function as a direct delegate for [MessageTransformingHandler].
+	 * @param function the function instance to use.
+	 * @param <P> the input type.
+	 */
+	inline fun <reified P> transformer(crossinline function: (P) -> Any) {
+		expectedType(P::class.java)
+		transformer<P, Any> { function(it) }
+	}
+
+}

spring-integration-core/src/test/java/org/springframework/integration/dsl/flows/IntegrationFlowTests.java

@@ -64,7 +64,7 @@
 import org.springframework.integration.dsl.PollerSpec;
 import org.springframework.integration.dsl.Pollers;
 import org.springframework.integration.dsl.QueueChannelSpec;
-import org.springframework.integration.dsl.TransformerSpec;
+import org.springframework.integration.dsl.TransformerEndpointSpec;
 import org.springframework.integration.dsl.Transformers;
 import org.springframework.integration.endpoint.AbstractEndpoint;
 import org.springframework.integration.endpoint.EventDrivenConsumer;
@@ -684,7 +684,7 @@ public IntegrationFlow flow2() {
 					.get();
 		}
 
-		private void payloadSerializingTransformer(TransformerSpec spec) {
+		private void payloadSerializingTransformer(TransformerEndpointSpec spec) {
 			spec.transformer(new PayloadSerializingTransformer())
 					.autoStartup(false)
 					.id("payloadSerializingTransformer");

spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/KotlinDslTests.kt

@@ -161,7 +161,10 @@ class KotlinDslTests {
 
 		val integrationFlow =
 			integrationFlow(publisher) {
-				transform<Message<Int>>({ it.payload * 2 }) { id("foo") }
+				transformWith {
+					transformer<Message<Int>> { it.payload * 2 }
+					id("foo")
+				}
 				channel(fluxChannel)
 			}
 
@@ -249,7 +252,10 @@ class KotlinDslTests {
 		@Bean
 		fun functionFlow() =
 			integrationFlow<Function<ByteArray, String>>({ beanName("functionGateway") }) {
-				transform(Transformers.objectToString()) { id("objectToStringTransformer") }
+				transformWith {
+					transformer(Transformers.objectToString())
+					id("objectToStringTransformer")
+				}
 				transform<String> { it.uppercase() }
 				split<Message<*>> { it.payload }
 				split<String>({ it }) { id("splitterEndpoint") }
@@ -292,7 +298,10 @@ class KotlinDslTests {
 		fun fixedSubscriberFlow() =
 			integrationFlow("fixedSubscriberInput", true) {
 				log<Any>(LoggingHandler.Level.WARN) { it.payload }
-				transform("payload") { id("spelTransformer") }
+				transformWith {
+					expression("payload")
+					id("spelTransformer")
+				}
 			}
 
 		@Bean

spring-integration-groovy/src/main/groovy/org/springframework/integration/groovy/dsl/GroovyIntegrationFlowDefinition.groovy

@@ -47,7 +47,7 @@ import org.springframework.integration.dsl.ResequencerSpec
 import org.springframework.integration.dsl.RouterSpec
 import org.springframework.integration.dsl.ScatterGatherSpec
 import org.springframework.integration.dsl.SplitterEndpointSpec
-import org.springframework.integration.dsl.TransformerSpec
+import org.springframework.integration.dsl.TransformerEndpointSpec
 import org.springframework.integration.dsl.WireTapSpec
 import org.springframework.integration.filter.MethodInvokingSelector
 import org.springframework.integration.handler.BridgeHandler
@@ -355,8 +355,8 @@ class GroovyIntegrationFlowDefinition {
 	 * @since 6.2
 	 */
 	GroovyIntegrationFlowDefinition transform(
-			@DelegatesTo(value = TransformerSpec, strategy = Closure.DELEGATE_FIRST)
-			@ClosureParams(value = SimpleType.class, options = 'org.springframework.integration.dsl.TransformerSpec')
+			@DelegatesTo(value = TransformerEndpointSpec, strategy = Closure.DELEGATE_FIRST)
+			@ClosureParams(value = SimpleType.class, options = 'org.springframework.integration.dsl.TransformerEndpointSpec')
 					Closure<?> transformerConfigurer) {
 
 		this.delegate.transformWith createConfigurerIfAny(transformerConfigurer)