Upgrade to Dokka 2.1.0

* Upgrade to Dokka 2.1.0

- Update `org.jetbrains.dokka` plugin from 2.0.0 to 2.1.0
- Remove Jackson 2.15.3 version resolution strategy workaround that
  was needed to avoid conflicts in Dokka 2.0.0
- Migrate from deprecated V1 tasks (`dokkaHtmlPartial`,
  `dokkaHtmlMultiModule`) to V2 API (`dokkaGeneratePublicationHtml`,
  `dokkaGenerate`)
- Replace `dokkaSourceSets.main` configuration block with
  `dokkaSourceSets.configureEach`
- Update `docsZip` task to depend on new
  `dokkaGeneratePublicationHtml` task and add explicit dependency on
  `:spring-integration-core:dokkaGenerate`

* Restore external documentation links for Dokka

- Restore external documentation links in spring-integration-core's
  `dokkaSourceSets` using the new `externalDocumentationLinks.
  register()` API instead of deprecated `externalDocumentationLink`
- Fix indentation of spring-integration-core's `dokka` configuration
  block to be properly scoped within the project
- Remove redundant `noJdkLink.set(false)` setting (false is default)
- Remove unnecessary root-level `dokka` configuration that was
  setting module name and output directory without effect
- Remove unused `dokkaGeneratePublicationHtml` task dependency from
  `docsZip` as `dokkaGenerate` already handles the generation
- Simplify dependency chain by relying solely on
  `:spring-integration-core:dokkaGenerate`
- Use root project var to determine root
- Move the out of core module
  This makes the dokka build available to all modules if necessary
- Only run the module in the core module

* Optimize Dokka to process selected modules only

- Refactor Dokka configuration to apply only to modules with Kotlin
  sources, reducing build overhead and improving performance for
  modules without Kotlin code.
- Remove deprecated commands

* Simplify Dokka configuration with auto-discovery

Replace static `dokkaProjects` list with dynamic Kotlin source
detection, eliminating manual maintenance and improving automation.

- Remove `dokkaProjects` list from ext block that required manual
  updates when adding Kotlin modules
- Move Dokka plugin and configuration back into main `javaProjects`
  configure block for simpler structure
- Update `docsZip` task to dynamically find projects with Kotlin
  sources using `javaProjects.findAll {it.file('src/main/kotlin').
  exists()}` instead of referencing static list
- Change output directory API from `buildDirectory.file('kdoc')` to
  `buildDirectory.dir('kdoc')` for semantically correct directory
  reference

* Use dokka plugin on required modules

Author: cppwfs

build.gradle

@@ -18,7 +18,7 @@ plugins {
     id 'base'
     id 'io.spring.nohttp' version '0.0.11' apply false
     id 'io.spring.dependency-management' version '1.1.7'
-    id 'org.jetbrains.dokka' version '2.0.0'
+    id 'org.jetbrains.dokka' version '2.1.0' apply false
     id 'org.antora' version '1.0.0'
     id 'io.spring.antora.generate-antora-yml' version '0.0.1'
     id 'com.google.protobuf' version '0.9.5' apply false
@@ -115,6 +115,7 @@ ext {
     ztZipVersion = '1.17'
 
     javaProjects = subprojects - project(':spring-integration-bom')
+
 }
 
 allprojects {
@@ -178,15 +179,6 @@ allprojects {
 
     }
 
-    // TODO Remove when Dokka 2.1.0 is released
-    configurations.matching { it.name.startsWith('dokka') }.configureEach {
-        resolutionStrategy.eachDependency {
-            if (requested.group.startsWith('com.fasterxml.jackson')) {
-                useVersion('2.15.3')
-            }
-        }
-    }
-
 }
 
 configure(javaProjects) { subproject ->
@@ -416,6 +408,30 @@ configure(javaProjects) { subproject ->
             }
         }
     }
+
+    // Process only the modules that require kotlin docs
+    if (file('src/main/kotlin')) {
+        apply plugin: 'org.jetbrains.dokka'
+        dokka {
+            dokkaPublications.html {
+                outputDirectory = rootProject.layout.buildDirectory.dir('kdoc')
+            }
+            dokkaSourceSets.configureEach {
+                sourceRoots.setFrom(file('src/main/kotlin'))
+                classpath.from(sourceSets['main'].runtimeClasspath)
+                externalDocumentationLinks.register("spring-integration-api") {
+                    url.set(uri("https://docs.spring.io/spring-integration/docs/$version/api/"))
+                    packageListUrl.set(file(rootProject.layout.buildDirectory.file('docs/javadoc/element-list')).toURI())
+                }
+                externalDocumentationLinks.register("reactor-core") {
+                    url.set(uri('https://projectreactor.io/docs/core/release/api/'))
+                }
+                externalDocumentationLinks.register("reactive-streams") {
+                    url.set(uri('https://www.reactive-streams.org/reactive-streams-1.0.3-javadoc/'))
+                }
+            }
+        }
+    }
 }
 
 project('spring-integration-test-support') {
@@ -477,7 +493,6 @@ project('spring-integration-cassandra') {
 project('spring-integration-core') {
     description = 'Spring Integration Core'
 
-    apply plugin: 'org.jetbrains.dokka'
     apply plugin: 'com.google.protobuf'
 
     dependencies {
@@ -520,27 +535,6 @@ project('spring-integration-core') {
         }
     }
 
-    dokkaHtmlPartial {
-        outputDirectory.set(new File('build', 'kdoc'))
-        dokkaSourceSets {
-            main {
-                sourceRoots.setFrom(file('src/main/kotlin'))
-                classpath.from(sourceSets['main'].runtimeClasspath)
-                noJdkLink.set(false)
-                externalDocumentationLink {
-                    url.set(new URL("https://docs.spring.io/spring-integration/docs/$version/api/"))
-                    packageListUrl.set(file('build/docs/javadoc/element-list').toURI().toURL())
-                }
-                externalDocumentationLink {
-                    url.set(new URL('https://projectreactor.io/docs/core/release/api/'))
-                }
-                externalDocumentationLink {
-                    url.set(new URL('https://www.reactive-streams.org/reactive-streams-1.0.3-javadoc/'))
-                }
-            }
-        }
-    }
-
     protobuf {
         protoc {
             artifact = "com.google.protobuf:protoc:$protobufVersion"
@@ -1107,12 +1101,6 @@ tasks.register('api') {
     dependsOn javadoc
 }
 
-dokkaHtmlMultiModule {
-    dependsOn 'api'
-    moduleName.set('spring-integration')
-    outputDirectory.set(file('build/kdoc'))
-}
-
 apply from: "${rootDir}/gradle/docs.gradle"
 
 tasks.register('schemaZip', Zip) {
@@ -1150,8 +1138,21 @@ tasks.register('schemaZip', Zip) {
     }
 }
 
+apply plugin: 'org.jetbrains.dokka'
+
+dependencies {
+    dokka project(':spring-integration-core')
+}
+
+dokka {
+    moduleName = "spring-integration"
+    dokkaPublications.html {
+        outputDirectory = project.layout.buildDirectory.dir('kdoc')
+    }
+}
+
 tasks.register('docsZip', Zip) {
-    dependsOn 'dokkaHtmlMultiModule'
+    dependsOn 'dokkaGenerate'
     group = 'Distribution'
     archiveClassifier = 'docs'
     description = "Builds -${archiveClassifier} archive containing api and reference " +
@@ -1165,7 +1166,7 @@ tasks.register('docsZip', Zip) {
         into 'api'
     }
 
-    from(dokkaHtmlMultiModule.outputDirectory) {
+    from(file('build/kdoc')) {
         into 'kdoc-api'
     }
 }