Configure Kotlin Spring plugin for proper proxy support

Update both Maven and Gradle build configurations to properly support
Kotlin with Spring Framework. The Kotlin Spring plugin automatically
handles making configuration classes open for proxying, eliminating the
need for manual 'open' modifiers.

Update maven generation scripts to handle kotlin plugin.
Add execution compile section so classes are included in the jar.
This can be tested via mvn clean package or to run mvn exec:java -Dexec.mainClass="org.springframework.integration.samples.helloworld.PollerApp"

Changes include:
- Add kotlin-spring and kotlin-allopen plugins to build configurations
- Remove unnecessary 'open' modifiers from @configuration classes
- Configure Kotlin Maven plugin with Spring compiler plugin
- Simplify QueueChannel initialization to use default capacity
- Update MessageProcessorMessageSource to use simpler lambda syntax
- Adjust logging configuration to reduce noise from Spring framework

Author: cppwfs

basic/helloworld-groovy/src/main/groovy/org/springframework/integration/samples/helloworld/HelloWorldConfig.groovy

@@ -43,7 +43,7 @@ class HelloWorldConfig {
 
 	@Bean
 	MessageChannel outputChannel() {
-		new QueueChannel(10)
+		new QueueChannel()
 	}
 
 	@Bean

basic/helloworld-kotlin/pom.xml

@@ -64,12 +64,12 @@
       <dependency>
         <groupId>org.jetbrains.kotlin</groupId>
         <artifactId>kotlin-stdlib</artifactId>
-        <version>${kotlin.version}</version>
+        <version>2.2.21</version>
       </dependency>
       <dependency>
         <groupId>org.jetbrains.kotlin</groupId>
         <artifactId>kotlin-reflect</artifactId>
-        <version>${kotlin.version}</version>
+        <version>2.2.21</version>
       </dependency>
       <dependency>
         <groupId>org.junit</groupId>
@@ -183,7 +183,6 @@
   </dependencies>
   <properties>
     <java.version>17</java.version>
-    <kotlin.version>2.2.21</kotlin.version>
   </properties>
   <repositories>
     <repository>
@@ -198,11 +197,21 @@
     </repository>
   </repositories>
   <build>
+    <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
+    <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
     <plugins>
       <plugin>
         <groupId>org.jetbrains.kotlin</groupId>
         <artifactId>kotlin-maven-plugin</artifactId>
-        <version>${kotlin.version}</version>
+        <version>2.2.21</version>
+        <configuration>
+          <args>
+            <arg>-Xjsr305=strict</arg>
+          </args>
+          <compilerPlugins>
+            <plugin>spring</plugin>
+          </compilerPlugins>
+        </configuration>
         <executions>
           <execution>
             <id>compile</id>
@@ -219,12 +228,13 @@
             </goals>
           </execution>
         </executions>
-        <configuration>
-          <jvmTarget>17</jvmTarget>
-          <args>
-            <arg>-Xjdk-release=17</arg>
-          </args>
-        </configuration>
+        <dependencies>
+          <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-maven-allopen</artifactId>
+            <version>2.2.21</version>
+          </dependency>
+        </dependencies>
       </plugin>
     </plugins>
   </build>

basic/helloworld-kotlin/src/main/kotlin/org/springframework/integration/samples/helloworld/HelloWorldConfig.kt

@@ -31,7 +31,7 @@ import org.springframework.messaging.MessageChannel
  */
 @Configuration(proxyBeanMethods = false)
 @EnableIntegration
-open class HelloWorldConfig {
+class HelloWorldConfig {
 
     /**
      * Creates the input channel for inbound messages.
@@ -43,19 +43,19 @@ open class HelloWorldConfig {
      * @return A [DirectChannel] instance for synchronous inbound message delivery
      */
     @Bean
-    open fun inputChannel() = DirectChannel()
+    fun inputChannel() = DirectChannel()
 
     /**
      * Creates the output channel for outbound messages.
      *
-     * A [QueueChannel] with capacity of 10 messages provides asynchronous,
+     * A [QueueChannel] with default capacity provides asynchronous,
      * buffered message delivery. Results from the integration flow are queued
      * and available for downstream consumption.
      *
-     * @return A [QueueChannel] instance with capacity of 10 messages
+     * @return A [QueueChannel] instance with default capacity.
      */
     @Bean
-    open fun outputChannel() = QueueChannel(10)
+    fun outputChannel() = QueueChannel()
 
     /**
      * Creates the Hello World business service.
@@ -66,7 +66,7 @@ open class HelloWorldConfig {
      * @return A [HelloService] instance
      */
     @Bean
-    open fun helloService() = HelloService()
+    fun helloService() = HelloService()
 
     /**
      * Defines the main integration flow for message processing.
@@ -77,7 +77,7 @@ open class HelloWorldConfig {
      * @return An IntegrationFlow representing the complete message flow
      */
     @Bean
-    open fun helloWorldFlow(inputChannel: MessageChannel, outputChannel: MessageChannel, helloService: HelloService) =
+    fun helloWorldFlow(inputChannel: MessageChannel, outputChannel: MessageChannel, helloService: HelloService) =
         integrationFlow(inputChannel) {
             handle(helloService, "sayHello")
             channel(outputChannel)

basic/helloworld-kotlin/src/main/kotlin/org/springframework/integration/samples/helloworld/PollerConfig.kt

@@ -21,7 +21,6 @@ import org.springframework.context.annotation.Configuration
 import org.springframework.integration.channel.NullChannel
 import org.springframework.integration.config.EnableIntegration
 import org.springframework.integration.dsl.integrationFlow
-import org.springframework.integration.endpoint.MessageProcessorMessageSource
 import org.springframework.integration.handler.LoggingHandler
 
 /**
@@ -32,7 +31,7 @@ import org.springframework.integration.handler.LoggingHandler
  */
 @Configuration(proxyBeanMethods = false)
 @EnableIntegration
-open class PollerConfig {
+class PollerConfig {
 
     /**
      * Defines a polling-based integration flow for periodic message generation.
@@ -45,9 +44,9 @@ open class PollerConfig {
      * @return An IntegrationFlow that periodically generates and logs timestamps, then discards them.
      */
     @Bean
-    open fun pollerFlow() =
+    fun pollerFlow() =
         integrationFlow(
-            MessageProcessorMessageSource { System.currentTimeMillis() },
+            { System.currentTimeMillis() },
                     { poller { it.fixedDelay(20000).maxMessagesPerPoll(2) } }) {
                 log(LoggingHandler.Level.INFO, "org.springframework.integration.samples.helloworld")
                 channel(NullChannel())

basic/helloworld-kotlin/src/main/resources/log4j2.xml

@@ -6,8 +6,9 @@
 		</Console>
 	</Appenders>
 	<Loggers>
-		<Logger name="org.springframework" level="info"/>
-		<Root level="info">
+		<Logger name="org.springframework" level="warn"/>
+		<Logger name="org.springframework.integration.samples.helloworld" level="info"/>
+		<Root level="warn">
 			<AppenderRef ref="Console"/>
 		</Root>
 	</Loggers>

build.gradle

@@ -10,6 +10,7 @@ buildscript {
 		classpath "org.springframework.boot:spring-boot-gradle-plugin:$springBootVersion"
 		classpath 'org.gretty:gretty:4.1.10'
 		classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:2.2.21'
+		classpath 'org.jetbrains.kotlin:kotlin-allopen:2.2.21'
 	}
 }
 
@@ -178,6 +179,56 @@ subprojects { subproject ->
 										}
 							}
 
+							if (subproject.plugins.hasPlugin('org.jetbrains.kotlin.jvm')) {
+								def kotlinVersion = '2.2.21'
+								def plugins = asNode().build?.find()?.plugins?.find()
+								if (!plugins) {
+									plugins = asNode().appendNode('build').with {
+										appendNode('sourceDirectory', '${project.basedir}/src/main/kotlin')
+										appendNode('testSourceDirectory', '${project.basedir}/src/test/kotlin')
+										appendNode('plugins')
+									}
+								}
+
+								plugins.appendNode('plugin')
+										.with {
+											appendNode('groupId', 'org.jetbrains.kotlin')
+											appendNode('artifactId', 'kotlin-maven-plugin')
+											appendNode('version', kotlinVersion)
+											appendNode('configuration').with {
+												appendNode('args').with {
+													appendNode('arg', '-Xjsr305=strict')
+												}
+												appendNode('compilerPlugins').with {
+													appendNode('plugin', 'spring')
+												}
+											}
+											appendNode('executions').with {
+												appendNode('execution').with {
+													appendNode('id', 'compile')
+													appendNode('phase', 'compile')
+													appendNode('goals').with {
+														appendNode('goal', 'compile')
+													}
+												}
+												appendNode('execution').with {
+													appendNode('id', 'test-compile')
+													appendNode('phase', 'test-compile')
+													appendNode('goals').with {
+														appendNode('goal', 'test-compile')
+													}
+												}
+											}
+											appendNode('dependencies').with {
+												appendNode('dependency').with {
+													appendNode('groupId', 'org.jetbrains.kotlin')
+													appendNode('artifactId', 'kotlin-maven-allopen')
+													appendNode('version', kotlinVersion)
+												}
+											}
+										}
+							}
+
 							def pomDeps = asNode().dependencies.find()
 							if (!pomDeps) {
 								pomDeps = asNode().appendNode('dependencies')
@@ -620,7 +671,8 @@ project('helloworld-groovy') {
 		api "org.springframework.integration:spring-integration-groovy"
 		testImplementation "org.apache.logging.log4j:log4j-core-test:$log4jVersion"
 		testImplementation "org.awaitility:awaitility:$awaitilityVersion"
-		testImplementation("org.assertj:assertj-core:$assertjVersion")	}
+		testImplementation("org.assertj:assertj-core:$assertjVersion")
+	}
 
 	tasks.register ('runHelloWorldApp', JavaExec) {
 		mainClass = 'org.springframework.integration.samples.helloworld.HelloWorldApp'
@@ -637,7 +689,8 @@ project('helloworld-groovy') {
 project('helloworld-kotlin') {
 	description = 'Hello World Sample for Kotlin Developers'
 
-	apply plugin: 'org.jetbrains.kotlin.jvm'
+	apply plugin: 'kotlin'
+	apply plugin: 'kotlin-spring'
 
 	dependencies {
 		api "org.apache.logging.log4j:log4j-core:$log4jVersion"
@@ -646,7 +699,8 @@ project('helloworld-kotlin') {
 		api "org.jetbrains.kotlin:kotlin-reflect"
 		testImplementation "org.apache.logging.log4j:log4j-core-test:$log4jVersion"
 		testImplementation "org.awaitility:awaitility:$awaitilityVersion"
-		testImplementation("org.assertj:assertj-core:$assertjVersion")	}
+		testImplementation("org.assertj:assertj-core:$assertjVersion")
+	}
 
 	tasks.register ('runHelloWorldApp', JavaExec) {
 		mainClass = 'org.springframework.integration.samples.helloworld.HelloWorldApp'