Spring ❤️ Kotlin #jjug

1. ‹#›© 2016 Pivotal Software, Inc. All rights reserved. ‹#›© 2016 Pivotal Software, Inc. All rights reserved. Spring ❤ Kotlin Toshiaki Maki (@making) tmaki@pivotal.io JJUG Night Seminar 2017 Feb 2017-02-20

2. © 2016 Pivotal Software, Inc. All rights reserved. Who am I ? • Toshiaki Maki (@making) https://ik.am • Sr. Solutions Architect @Pivotal • Spring ☘ / Cloud Foundry ☁ / Concourse ✈ / BOSH 🐚 bit.ly/hajiboot2

14. © 2016 Pivotal Software, Inc. All rights reserved. package com.example    import org.springframework.boot.SpringApplication  import org.springframework.boot.autoconfigure.SpringBootApplication    @SpringBootApplication  class DemoApplication    fun main(args: Array<String>) {  SpringApplication.run(DemoApplication::class.java, *args)  } 

16. © 2016 Pivotal Software, Inc. All rights reserved. package com.example    import org.springframework.web.bind.annotation.GetMapping  import org.springframework.web.bind.annotation.RestController    @RestController  class HelloController {  @GetMapping("/")  fun hello() = "Hello World!"  }  

17. © 2016 Pivotal Software, Inc. All rights reserved. package com.example    import org.springframework.web.bind.annotation.GetMapping  import org.springframework.web.bind.annotation.RestController    @RestController  class HelloController {  @GetMapping("/")  fun hello() = "Hello World!"  }  

23. © 2016 Pivotal Software, Inc. All rights reserved. Cglib and Spring (Pseudo Code) class AppConfig$$ extends AppConfig { @Override  RestTemplate restTemplate() { if (context.contains("restTemplate")) { return context.get("restTemplate"); } return super.restTemplate(); }  }

24. © 2016 Pivotal Software, Inc. All rights reserved. Cglib and Spring (Pseudo Code) class AppConfig$$ extends AppConfig { @Override  RestTemplate restTemplate() { if (context.contains("restTemplate")) { return context.get("restTemplate"); } return super.restTemplate(); }  } Methods in Kotlin are final by default !! open removes final

25. © 2016 Pivotal Software, Inc. All rights reserved. <plugin>  <artifactId>kotlin-maven-plugin</artifactId>  <groupId>org.jetbrains.kotlin</groupId>  <version>${kotlin.version}</version>  <configuration>  <compilerPlugins>  <plugin>spring</plugin>  </compilerPlugins>  </configuration> </plugin>

32. © 2016 Pivotal Software, Inc. All rights reserved. Spring Framework 5 •Java 8 baseline, Java 9 compatibility •Reactive Support & Spring WebFlux •Router Functions •Performance improvements •HTTP/2 support •Kotlin support

37. © 2016 Pivotal Software, Inc. All rights reserved. package com.example; public class Foo { public <T> T create(Class<T> clazz) { try { return clazz.newInstance(); } catch (Exception e) { throw new IllegalStateException(e); } } }

42. © 2016 Pivotal Software, Inc. All rights reserved. Extension Functions •Extends a class with new functionality without having to inherit from the class •https://kotlinlang.org/docs/reference/ extensions.html#extension-functions

47. © 2016 Pivotal Software, Inc. All rights reserved. Extension Functions package com.example import kotlin.reflect.KClass fun <T : Any> Foo.create(kclass: KClass<T>) = create(kclass.java)  FooExtensions.kt

48. © 2016 Pivotal Software, Inc. All rights reserved. Extension Functions package com.example import kotlin.reflect.KClass fun <T : Any> Foo.create(kclass: KClass<T>) = create(kclass.java)  👇 FooExtensions.kt

50. © 2016 Pivotal Software, Inc. All rights reserved. Reified type parameters •Access a type passed to us as a parameter •https://kotlinlang.org/docs/reference/inline- functions.html#reified-type-parameters

72. © 2016 Pivotal Software, Inc. All rights reserved. RestTemplate // Java List<Foo> foos = restTemplate .exchange("http://abc.io", HttpMethod.GET, null, new ParameterizedTypeReference<List<Foo>>() {}).getBody();

73. © 2016 Pivotal Software, Inc. All rights reserved. RestTemplate // Java List<Foo> foos = restTemplate .exchange("http://abc.io", HttpMethod.GET, null, new ParameterizedTypeReference<List<Foo>>() {}).getBody(); 💩

78. © 2016 Pivotal Software, Inc. All rights reserved. Spring Framework 5 •Java 8 baseline, Java 9 compatibility •Reactive Support & Spring WebFlux •Router Functions •Performance improvements •HTTP/2 support •Kotlin support

79. © 2016 Pivotal Software, Inc. All rights reserved. Spring Framework 5 •Java 8 baseline, Java 9 compatibility •Reactive Support & Spring WebFlux •Router Functions •Performance improvements •HTTP/2 support •Kotlin support 👇 👇

80. © 2016 Pivotal Software, Inc. All rights reserved. Spring Framework 5 •Java 8 baseline, Java 9 compatibility •Reactive Support & Spring WebFlux •Router Functions •Performance improvements •HTTP/2 support •Kotlin support 👇 👇 🤔

82. © 2016 Pivotal Software, Inc. All rights reserved. WebMVC + @Controller in Java @RestController public class UserController { private final UserRepository repo; UserController(UserRepository repo) {/.../} @GetMapping List<User> users() { return repo.findAll(); } }

83. © 2016 Pivotal Software, Inc. All rights reserved. WebFlux + @Controller in Java @RestController public class UserController { private final ReactiveUserRepository repo; UserController(ReactiveUserRepository repo) {/.../} @GetMapping Flux<User> users() { return repo.findAll(); } }

84. © 2016 Pivotal Software, Inc. All rights reserved. WebFlux + @Controller in Java @RestController public class UserController { private final ReactiveUserRepository repo; UserController(ReactiveUserRepository repo) {/.../} @GetMapping Flux<User> users() { return repo.findAll(); } } Non-Blocking!!

89. © 2016 Pivotal Software, Inc. All rights reserved. Other Kotlin Support •Functional Bean Registration with Kotlin •WebFlux functional API, the Kotlin way •Leveraging Kotlin nullable information •Kotlin Script based templates •... •https://speakerdeck.com/sdeleuze/functional- web-applications-with-kotlin-and-spring-5?

95. © 2016 Pivotal Software, Inc. All rights reserved. Resources • https://spring.io/blog/2017/01/04/introducing-kotlin-support- in-spring-framework-5-0 • https://speakerdeck.com/sdeleuze • https://blog.ik.am/entries/407