WIXLIB

Kotlin 1.4 Online EventThe State of KotlinSupport in SpringSébastien Deleuze@sdeleuzeOctober 15, 2020

Spring is the server-side leader on the JVMSource: a Picture of Java in 2020, JetBrains

First class support for Java and Kotlin

More Spring Boot projectsgenerated with Kotlin each year.

Let’s focus on Kotlin today

Getting started

Start your project on https://start.spring.io

Minimal Spring Boot Kotlin application

Gradle Kotlin DSL

Also available in IDEsIntelliJ IDEA UltimateVS code

Follow the tutorial on https://spring.io/guides

Spring Framework documentation in Kotlin

Choose your style

Choose your web server stackSpring MVCTomcatPersistenceJPAJDBCRedisMongo.NoDo I needasynchronousor reactiveprogramming?YesSpring WebFluxwith CoroutinesNettySpring DataPersistenceSpring DataReactivewith CoroutinesR2DBCRedisMongo.

Choose your programming model

Do you prefer rticle")class ArticleController(private val repository: ArticleRepository) {@GetMapping("/")fun findAll() g("/{slug}")fun findOne(@PathVariable slug: String) repository.findBySlug(slug) ?:throw ResponseStatusException(NOT FOUND)}

Or functional APIs?@Beanfun route(repository: ArticleRepository) router {"/api/article".nest {GET("/") ))}GET("/{slug}") {val slug it.pathVariable("slug")val article repository.findBySlug(slug) ?:throw ResponseStatusException(NOT FOUND)ok().body(article)}}}

Spring supports both,so up to you.

Coroutines

Allow to go reactive with agreat trade-off betweenimperative and functionalprogramming.

Coroutines are the default way togo reactive in Spring with Kotlin.

First class Coroutines support Spring WebFluxSpring MVC (new in Spring Boot 2.4 Spring Data ReactiveSpring Messaging (RSocket)Spring Vault

Suspending functionsSpring MVC and WebFlux@GetMapping("/api/banner")suspend fun suspendingEndpoint(): Banner {delay(10)return Banner("title", "Lorem ipsum")}

FlowSpring MVC and WebFlux@GetMapping("/banners")suspend fun flow(): Flow Banner T EVENT STREAM).retrieve().bodyToFlow String ().map { Banner("title", it) }

Multiplatform

Multiplatform

kotlinx.serialization

kotlinx.serialization supportNew in Spring Boot 2.4 More lightweight than JacksonDesigned for KotlinMultiplatform serializationAllows same code for model and validationacross server, frontend and ring-boot-starter-web") {exclude(module tbrains.kotlinx:kotlinx-serialization-json:1.0.0")

Kotlin/JS

Kotlin/WASM has a huge potential

RSocket

veStreams

.PythonRSocket.NETGoC ReactiveStreamsJavaScriptKotlinJavaRSocketReactor

RSocket support in Spring messagingclass MessageHandler(private val builder: RSocketRequester.Builder) {// .}suspend fun stream(request: ServerRequest): ServerResponse {val requester builder.dataMimeType(APPLICATION CBOR).connectTcpAndAwait("localhost", 9898)val replies ssor).retrieveFlow Message ()val broadcast requester.route("bot.broadcast").retrieveFlow Message ()val messages flowOf(replies, processor.asFlow(), broadcast).flattenMerge()return ok().sse().bodyAndAwait(messages)}

rsocket-kotlin

Other key points

100% of Spring Framework APIwith null-safety annotations no NPE for Spring applicationswritten in Kotlin

ConfigurationProperties data ("blog")data class BlogProperties(val title: String, val banner: Banner) {data class Banner(val title: String? null, val content: String)}

Spring Security Kotlin DSLNew in Spring Security 5.4override fun configure(http: HttpSecurity) {http {authorizeRequests {authorize("/css/**", permitAll)authorize("/user/**", hasAuthority("ROLE USER"))}formLogin {loginPage "/log-in"}}}

Spring Boot native applicationsWith GraalVM native

EXESpring rimage

JVM and native executables offer differenttrade-offs

Instant startup and cheaper hostingSpring Boot on JVM,4 vCPU, 1G RAMSpring Boot on Native,1 vCPU, 256M RAM

Spring support for native executablesIncubating support inspring-graalvm-native plugin(Spring Boot 2 baseline)GraalVM fixesand improvementsFirst class supportin Spring Boot 3TodayDec 2020BetaSpring Boot 3release

Demo

What’s next?Programmatic configuration for Spring Boot using a Kotlin DSL

Spring Fu is an incubator for a functionalflavor of Spring BootKoFuJaFu

What is the same than Spring Boot? https://start.spring.ioBased on Spring Boot infrastructureSpring configuration for the JVM ecosystemDependency managementStartersActuatorsStandalone executable JAR or container deployment

What changes?Spring Boot regular flavorSpring Fu flavorConventions and automaticconfigurationExplicit declarationAnnotations-based configurationFunctional configurationReflection-based infrastructureLambda-based infrastructureProduction readyIncubating

Spring Boot configured with KoFuval app webApplication {beans {bean SampleService ()bean SampleHandler ()}webMvc {port if (profiles.contains("test")) 8181 else 8080router {val handler ref SampleHandler ()GET("/", handler::hello)GET("/api", handler::json)}converters {string()jackson {indentOutput true}}}}fun main() {app.run()}

pring-fu

Thanks!Have a nice Kotlin!@sdeleuze

Support in Spring Sébastien Deleuze. Spring is the server-side leader on the JVM Source: a Picture of Java in 2020, JetBrains . Spring Framework documentation in Kotlin. Choose your style. Choose your web server stack Do I need asynchronous . 100% of Spring Framework API with null-safety annotations no NPE for Spring applications