Add Kotlin alternatives to Java samples

buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java

@@ -46,9 +46,9 @@ void apply(Project project) {
 		project.getPlugins().withId("org.jetbrains.kotlin.jvm", (plugin) -> {
 			project.getTasks().withType(KotlinCompile.class, (compile) -> {
 				KotlinJvmOptions kotlinOptions = compile.getKotlinOptions();
-				kotlinOptions.setApiVersion("1.3");
-				kotlinOptions.setLanguageVersion("1.3");
-				kotlinOptions.setAllWarningsAsErrors(true);
+				kotlinOptions.setApiVersion("1.6");
+				kotlinOptions.setLanguageVersion("1.6");
+				kotlinOptions.setAllWarningsAsErrors(false);
 				List<String> freeCompilerArgs = new ArrayList<>(compile.getKotlinOptions().getFreeCompilerArgs());
 				freeCompilerArgs.add("-Xsuppress-version-warnings");
 				compile.getKotlinOptions().setFreeCompilerArgs(freeCompilerArgs);

gradle.properties

@@ -7,4 +7,4 @@ org.gradle.jvmargs=-Xmx2g -Dfile.encoding=UTF-8
 kotlinVersion=1.6.10
 tomcatVersion=9.0.56
 
-kotlin.stdlib.default.dependency=false
+kotlin.stdlib.default.dependency=true

spring-boot-project/spring-boot-docs/build.gradle

@@ -4,6 +4,7 @@ plugins {
 	id "org.asciidoctor.jvm.convert"
 	id "org.springframework.boot.conventions"
 	id "org.springframework.boot.deployed"
+	id 'org.jetbrains.kotlin.jvm'
 }
 
 description = "Spring Boot Docs"
@@ -173,6 +174,7 @@ dependencies {
 	testRuntimeOnly("org.springframework:spring-jdbc")
 
 	testSlices(project(path: ":spring-boot-project:spring-boot-test-autoconfigure", configuration: "testSliceMetadata"))
+	implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
 }
 
 task dependencyVersions(type: org.springframework.boot.build.constraints.ExtractVersionConstraints) {
@@ -324,6 +326,9 @@ syncDocumentationSourceForAsciidoctor {
 	from("src/main/groovy") {
 		into "main/groovy"
 	}
+	from("src/main/kotlin") {
+		into "main/kotlin"
+	}
 	from("src/main/resources") {
 		into "main/resources"
 	}
@@ -348,6 +353,9 @@ syncDocumentationSourceForAsciidoctorMultipage {
 	from("src/main/groovy") {
 		into "main/groovy"
 	}
+	from("src/main/kotlin") {
+		into "main/kotlin"
+	}
 	from("src/main/resources") {
 		into "main/resources"
 	}
@@ -372,6 +380,9 @@ syncDocumentationSourceForAsciidoctorPdf {
 	from("src/main/groovy") {
 		into "main/groovy"
 	}
+	from("src/main/kotlin") {
+		into "main/kotlin"
+	}
 	from("src/main/resources") {
 		into "main/resources"
 	}
@@ -427,3 +438,16 @@ publishing {
 		}
 	}
 }
+repositories {
+	mavenCentral()
+}
+compileKotlin {
+	kotlinOptions {
+		jvmTarget = "1.8"
+	}
+}
+compileTestKotlin {
+	kotlinOptions {
+		jvmTarget = "1.8"
+	}
+}

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/cloud-foundry.adoc

@@ -47,7 +47,13 @@ If you expect the Cloud Foundry endpoints to always be available at `/cloudfound
 The configuration differs, depending on the web server in use.
 For Tomcat, you can add the following configuration:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/cloudfoundry/customcontextpath/MyCloudFoundryConfiguration.java[]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/cloudfoundry/customcontextpath/MyCloudFoundryConfiguration.kt[]
+----

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/endpoints.adoc

@@ -328,10 +328,16 @@ If you wish to configure custom security for HTTP endpoints (for example, to all
 
 A typical Spring Security configuration might look something like the following example:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/security/typical/MySecurityConfiguration.java[]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/security/typical/MySecurityConfiguration.kt[]
+----
 
 The preceding example uses `EndpointRequest.toAnyEndpoint()` to match a request to any endpoint and then ensures that all have the `ENDPOINT_ADMIN` role.
 Several other matcher methods are also available on `EndpointRequest`.
@@ -351,10 +357,16 @@ You can do so by changing the configprop:management.endpoints.web.exposure.inclu
 
 Additionally, if Spring Security is present, you would need to add custom security configuration that allows unauthenticated access to the endpoints, as the following example shows:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/security/exposeall/MySecurityConfiguration.java[]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/security/exposeall/MySecurityConfiguration.kt[]
+----
 
 NOTE: In both of the preceding examples, the configuration applies only to the actuator endpoints.
 Since Spring Boot's security configuration backs off completely in the presence of any `SecurityFilterChain` bean, you need to configure an additional `SecurityFilterChain` bean with rules that apply to the rest of the application.
@@ -443,10 +455,16 @@ If both Jersey and Spring MVC are available, Spring MVC is used.
 
 The following example exposes a read operation that returns a custom object:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/implementingcustom/MyEndpoint.java[tag=read]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/implementingcustom/MyEndpoint.kt[tag=read]
+----
 
 You can also write technology-specific endpoints by using `@JmxEndpoint` or `@WebEndpoint`.
 These endpoints are restricted to their respective technologies.
@@ -480,10 +498,16 @@ Consider the following JSON request body:
 
 You can use this to invoke a write operation that takes `String name` and `int counter` parameters, as the following example shows:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/implementingcustom/MyEndpoint.java[tag=write]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/implementingcustom/MyEndpoint.kt[tag=write]
+----
 
 TIP: Because endpoints are technology agnostic, only simple types can be specified in the method signature.
 In particular, declaring a single parameter with a `CustomData` type that defines a `name` and `counter` properties is not supported.
@@ -759,10 +783,16 @@ You need to provide an implementation of the `health()` method and return a `Hea
 The `Health` response should include a status and can optionally include additional details to be displayed.
 The following code shows a sample `HealthIndicator` implementation:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/health/writingcustomhealthindicators/MyHealthIndicator.java[]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/health/writingcustomhealthindicators/MyHealthIndicator.kt[]
+----
 
 NOTE: The identifier for a given `HealthIndicator` is the name of the bean without the `HealthIndicator` suffix, if it exists.
 In the preceding example, the health information is available in an entry named `my`.
@@ -837,10 +867,17 @@ If you need to register a regular `HealthContributor`, you should wrap it with `
 To provide custom health information from a reactive API, you can register Spring beans that implement the {spring-boot-actuator-module-code}/health/ReactiveHealthIndicator.java[`ReactiveHealthIndicator`] interface.
 The following code shows a sample `ReactiveHealthIndicator` implementation:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/health/reactivehealthindicators/MyReactiveHealthIndicator.java[]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/health/reactivehealthindicators/MyReactiveHealthIndicator.kt[]
+----
+
 
 TIP: To handle the error automatically, consider extending from `AbstractReactiveHealthIndicator`.
 
@@ -1283,10 +1320,16 @@ To provide custom application information, you can register Spring beans that im
 
 The following example contributes an `example` entry with a single value:
 
-[source,java,indent=0,subs="verbatim"]
+.Java
+[source,java,indent=0,subs="verbatim",role="primary"]
 ----
 include::{docs-java}/actuator/endpoints/info/writingcustominfocontributors/MyInfoContributor.java[]
 ----
+.Kotlin
+[source,kotlin,indent=0,subs="verbatim",role="secondary"]
+----
+include::{docs-kotlin}/actuator/endpoints/info/writingcustominfocontributors/MyInfoContributor.kt[]
+----
 
 If you reach the `info` endpoint, you should see a response that contains the following additional entry: