Spring 5 and Kotlin

With Spring 5 now having dedicated Kotlin support, let’s have a look into the features that are designed to make these technologies work seamless together.

Transcript

1. SPRING 5 & KOTLIN
   

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

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4. SPRING 5
   WHAT’S NEW?
   

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5. SPRING 5
   REACTOR
   Project Reactor
   

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6. SPRING 5
   REACTIVE STREAMS
   

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7. SPRING 5
   REACTOR
   Project Reactor
   

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8. 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
   

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9. SPRING 5
   REACTIVE STREAMS
   PUBLISHER SUBSCRIBER
   Subscribe then

   request(n) data

   (Backpressure)
   0..N data then

   0..1 (Error | Complete)
   

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

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13. SPRING 5
    WEBFLUX
    

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14. 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
    

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15. SPRING 5
    WHAT’S NEW?
    

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17. DEMO
    SPRING KOTLIN
    

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

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

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24. 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"
    }
    }
    

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

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26. 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)
    

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

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28. 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)
    }
    

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

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30. 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+)
    

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31. 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()
    

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32. 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) = ...
    

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33. 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()
    

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34. 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)
    

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35. 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
    

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

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37. 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
    

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38. 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
    

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39. 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")
    

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40. SPRING & KOTLIN
    KOTLIN SCRIPT BASED TEMPLATES
    import io.spring.demo.*
    """
    ${include("header")}
    ${i18n("title")}
    
    ${users.joinToLine{ "${i18n("user")} ${it.firstname} ${it.lastname}" }}
    
    ${include("footer")}
    """
    

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41. SPRING 5
    WEBFLUX
    

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42. 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
    }
    

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43. TEXT
    WEBFLUX
    

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44. 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
    }
    

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

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46. 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)),
    { ... }
    

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47. 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)),
    { ... }
    

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48. 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) { ... }
    }
    

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49. 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 {
    ...
    }
    }
    

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50. 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)
    }
    }
    

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

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52. 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())
    }
    

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53. 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!" })
    }
    

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54. SPRING 5
    ❤️
    

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