SPRING 5 & KOTLIN

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SPRING 5 WHAT’S NEW? ▸ Core framework revision ▸ Core container updates ▸ Reactive programming model

SPRING 5 WHAT’S NEW?

SPRING 5 REACTOR Project Reactor

SPRING 5 REACTIVE STREAMS

SPRING 5 REACTOR Project Reactor

SPRING 5 REACTOR Reactive core non-blocking foundation
 interacts with Java 8
 functional API, Completable
 Future, Streams Non-blocking IPC suited for microservices architecture
 backpressure-ready network engines
 (HTTP / Websockets / TCP / UDP)
 reactive encoding/decoding Typed [0|1|N] sequences reactive composable API
 Flux[N]
 Mono[0/1]
 implements Reactive Extensions

SPRING 5 REACTIVE STREAMS PUBLISHER SUBSCRIBER Subscribe then
 request(n) data
 (Backpressure) 0..N data then
 0..1 (Error | Complete)

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SPRING 5 WHAT’S NEW? ▸ Core framework revision ▸ Core container updates ▸ Reactive programming model ▸ WebFlux: reactive HTTP and WebSocket clients / reactive server applications

SPRING 5 WEBFLUX

SPRING 5 WHAT’S NEW? ▸ Core framework revision ▸ Core container updates ▸ Reactive programming model ▸ WebFlux: reactive HTTP and WebSocket clients / reactive server applications ▸ Functional, Java 8 Lambda style routing and handling ▸ Testing improvements

SPRING 5 WHAT’S NEW?

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DEMO SPRING KOTLIN

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SPRING BOOT & KOTLIN APPLICATION CONTEXT @SpringBootApplication class Application fun main(args: Array) { SpringApplication.run(Application ::class.java, *args) }

SPRING BOOT & KOTLIN CONTROLLER @RestController class HelloKotlinController { @GetMapping("/hello") fun hello(): String { return "Hello world" } }

SPRING BOOT & KOTLIN CONTROLLER TEST @RunWith(SpringRunner ::class) @SpringBootTest( classes = arrayOf(Application ::class), webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) class HelloKotlinControllerTest { @Autowired lateinit var testRestTemplate: TestRestTemplate @Test fun `hello endpoint should return hello world`() { val result = testRestTemplate.getForEntity("/hello", String ::class.java) result.shouldNotBeNull() result.statusCode shouldEqual HttpStatus.OK result.body shouldEqualTo "Hello world" } }

SPRING BOOT & KOTLIN DOMAIN data class GotCharacter(val firstName: String, val lastName: String, val age: Int, val actor: String, val id: Long = -1)

SPRING BOOT & KOTLIN DOMAIN @Entity data class GotCharacter(val firstName: String, val lastName: String, val age: Int, val actor: String, @Id @GeneratedValue(strategy = GenerationType.AUTO) val id: Long = -1)

SPRING BOOT & KOTLIN REPOSITORY interface GotCharacterRepository: CrudRepository { fun findByLastName(lastName: String): Iterable }

SPRING BOOT & KOTLIN CONTROLLER @RestController class GotController(private val repository: GotCharacterRepository) { @GetMapping("/") fun findAll() = repository.findAll() @GetMapping("/{lastName}") fun findByLastName(@PathVariable lastName: String) = repository.findByLastName(lastName) }

KOTLIN SUPPORT: SPRING MVC, SPRING WEBFLUX, RESTTEMPLATE, SPRING BOOT 2, … Spring Framework 5 TEXT

SPRING & KOTLIN NULL-SAFETY OF SPRING FRAMEWORK API ▸ Spring 5 introduces non-null API declaration for all packages ▸ Explicitly nullable arguments and return values annotated as such ▸ ➜ Spring framework APIs = null-safe from Kotlin side (Kotlin 1.1.50+)

SPRING & KOTLIN NULL-SAFETY OF SPRING FRAMEWORK API ▸ Spring 5 introduces non-null API declaration for all packages ▸ Explicitly nullable arguments and return values annotated as such ▸ ➜ Spring framework APIs = null-safe from Kotlin side (Kotlin 1.1.50+) @NonNullApi package org.springframework.core; /** * Return the "Cache-Control" header value. * @return {@code null} if no directive was added, or the header value otherwise */ @Nullable public String getHeaderValue()

SPRING & KOTLIN LEVERAGE KOTLIN NULLABLE INFORMATION IN SPRING ANNOTATIONS // "GET /foo" and "GET /foo?bar=baz" are allowed @GetMapping("/foo") fun foo(@RequestParam bar: String?) = ... // "GET /foo?bar=baz" is allowed and "GET /foo" will error @GetMapping("/foo") fun foo(@RequestParam bar: String) = ...

SPRING & KOTLIN EXTENSION: REIFIED TYPE PARAMETERS // Java Repo repoInfo = restTemplate.getForObject(url, Repo.class); Flux users = client.get().retrieve().bodyToFlux(User.class) // Kotlin val repo: Repo = restTemplate.getForObject(url) val users = client.get().retrieve().bodyToFlux() // or (both are equivalent) val users : Flux = client.get().retrieve().bodyToFlux()

SPRING & KOTLIN EXTENSION: REIFIED TYPE PARAMETERS ResponseEntity> response = restTemplate.exchange(uri, HttpMethod.GET, this.httpEntity, new ParameterizedTypeReference>() {}); inline fun RestOperations.getForObject(url: String, vararg uriVariables: Any) = getForObject(url, T ::class.java, *uriVariables)

SPRING & KOTLIN REACTOR KOTLIN BUILTIN SUPPORT ▸ Mono, Flux, StepVerifier APIs ▸ Kotlin extensions ▸ any class instance to Mono instance with foo.toMono() ▸ create Flux from Java 8 Streams wih stream.toFlux() ▸ extensions for Iterable, CompletableFuture, Throwable

SPRING & KOTLIN KOTLIN-SPRING PLUGIN ▸ Kotlin classes = final by default ➜ add open keyword on each class / member functions of Spring beans

SPRING & KOTLIN KOTLIN-SPRING PLUGIN ▸ Kotlin classes = final by default ➜ add open keyword on each class / member functions of Spring beans ▸ @Component
 @Async
 @Transactional
 @Cacheable

SPRING & KOTLIN KOTLIN-SPRING PLUGIN ▸ Kotlin classes = final by default ➜ add open keyword on each class / member functions of Spring beans ▸ @Component
 @Async
 @Transactional
 @Cacheable ▸ Meta-annotations support: @Configuration, @Controller, @RestController, @Service, @Repository

SPRING & KOTLIN GRADLE: KOTLIN DSL plugins { val kotlinVersion = "1.1.50" id("org.jetbrains.kotlin.jvm") version kotlinVersion id("org.jetbrains.kotlin.plugin.spring") version kotlinVersion id("org.jetbrains.kotlin.plugin.noarg") version kotlinVersion id("io.spring.dependency-management") version "1.0.3.RELEASE" } apply { plugin("kotlin") plugin("kotlin-spring") plugin("kotlin-jpa") plugin("org.springframework.boot") } version = "0.0.1-SNAPSHOT" tasks { withType { kotlinOptions { jvmTarget = "1.8" freeCompilerArgs = listOf("-Xjsr305=strict") } } } dependencies { compile("org.jetbrains.kotlin:kotlin-stdlib") compile("org.jetbrains.kotlin:kotlin-reflect") compile("org.springframework.boot:spring-boot-starter-web") compile("org.springframework.boot:spring-boot-starter-data-jpa") compile("org.springframework.boot:spring-boot-starter-actuator") compile("com.h2database:h2") compile("com.fasterxml.jackson.module:jackson-module-kotlin") testCompile("org.springframework.boot:spring-boot-starter-test") testCompile("org.amshove.kluent:kluent:1.29")

SPRING & KOTLIN KOTLIN SCRIPT BASED TEMPLATES import io.spring.demo.* """ ${include("header")}

${i18n("title")}

${users.joinToLine{ "
• ${i18n("user")} ${it.firstname} ${it.lastname}
" }}

${include("footer")} """

SPRING 5 WEBFLUX

SPRING & KOTLIN WEBFLUX ANNOTATION-BASED @RestController class ReactiveGotController(private val repository: ReactiveGotRepository) { @GetMapping("/reactive/characters") fun findAll() = repository.findAll() @GetMapping("/reactive/character/{id}") fun findOne(@PathVariable id: String) = repository.findById(id) @PostMapping("/reactive/character") fun save(@RequestBody character: GotCharacter) = repository.save(character) } interface ReactiveGotRepository { fun findAll(): Flux fun findById(id: String): Mono fun save(character: GotCharacter): Mono }

TEXT WEBFLUX

SPRING & KOTLIN WEBFLUX ANNOTATION BASED @RestController class ReactiveGotController(private val repository: ReactiveGotRepository) { @GetMapping("/reactive/characters") fun findAll() = repository.findAll() @GetMapping("/reactive/character/{id}") fun findOne(@PathVariable id: String) = repository.findById(id) @PostMapping("/reactive/character") fun save(@RequestBody character: GotCharacter) = repository.save(character) } interface ReactiveGotRepository { fun findAll(): Flux fun findById(id: String): Mono fun save(character: GotCharacter): Mono }

SPRING & KOTLIN FUNCTIONAL STYLE // Annotation-based Java @RequestMapping("/quotes/feed", produces = TEXT_EVENT_STREAM_VALUE) public Flux fetchQuotesStream() { ... }

SPRING & KOTLIN FUNCTIONAL STYLE // Annotation-based Java @RequestMapping("/quotes/feed", produces = TEXT_EVENT_STREAM_VALUE) public Flux fetchQuotesStream() { ... } // Functional Java without static imports RouterFunctions.route( RequestPredicates.path("/quotes/feed") .and(RequestPredicates.accept(MediaType.TEXT_EVENT_STREAM)), { ... }

SPRING & KOTLIN FUNCTIONAL STYLE // Annotation-based Java @RequestMapping("/quotes/feed", produces = TEXT_EVENT_STREAM_VALUE) public Flux fetchQuotesStream() { ... } // Functional Java with static imports route( path("/quotes/feed").and(accept(TEXT_EVENT_STREAM)), { ... }

SPRING & KOTLIN FUNCTIONAL STYLE // Annotation-based Java @RequestMapping("/quotes/feed", produces = TEXT_EVENT_STREAM_VALUE) public Flux fetchQuotesStream() { ... } // Functional Kotlin router { "/quotes/feed" and accept(TEXT_EVENT_STREAM) { ... } }

SPRING & KOTLIN FUNCTIONAL STYLE @Configuration class ApplicationRoutes(val userHandler: UserHandler, val blogHandler: BlogHandler, val shopRepository: ShopRepository) { @Bean fun appRouter() = router { GET("/users", userHandler ::fetchAll) GET("/users/{id}", userHandler ::fetch) } @Bean fun nestedRouter() = router { ... } @Bean fun dynamicRouter() = router { ... } }

SPRING & KOTLIN NESTED ROUTING @Bean fun nestedRouter() = router { ("/blog" and accept(MediaType.TEXT_HTML)).nest { GET("/", blogHandler ::findAllView) GET("/{slug}", blogHandler ::findOneView) } ("/api/blog" and accept(APPLICATION_JSON)).nest { GET("/", blogHandler ::findAll) GET("/{id}", blogHandler ::findOne) POST("/", blogHandler ::create) } }

SPRING & KOTLIN DYNAMIC ROUTING @Bean fun dynamicRouter() = router { shopRepository.findAll() .toIterable() .forEach { shop -> GET("/${shop.id}") { req -> shopHandler.homepage(shop, req) } } }

SPRING & KOTLIN HANDLER @Component class EventHandler(val repository: EventRepository) { fun findOne(req: ServerRequest) = ok().json().body(repository.findOne(req.pathVariable("id"))) fun findAll(req: ServerRequest) = ok().json().body(repository.findAll()) }

SPRING & KOTLIN HANDLER @Component class NewsHandler { fun newsView(req: ServerRequest) = ok().render("news") fun newsSse(req: ServerRequest) = ok() .contentType(TEXT_EVENT_STREAM) .body(Flux.interval(ofMillis(100)).map { "Hello $it!" }) }

SPRING 5 ❤️