End-to-end Kotlin in a Java Enterprise [CON1714, JavaOne 2017]

Venue: Moscone West - Room 2012; San Francisco, CA.
Time: 11:00AM - 11:45AM, 2nd October 2017
Speakers: @oluwasayo_ and @kingsleyadio
Tags: Kotlin, Java, JavaEE, Android, Spring, Maven, Gradle, Vaadin, KAPT, IntelliJ, Eclipse, NetBeans, AS

1. End-to-end Kotlin In a Java Enterprise
2. About us
3. Sayo Oladeji • Developer at Vaadin, Finland • Works on the Pro Tools team, responsible for commercial products like Vaadin Charts, TestBench, etc • Lover of the English Premier League • Twitter: @oluwasayo_
4. Kingsley Adio • Software Developer at HelloFresh, Germany • Eats Nougat for a living (Android) • Kotlin enthusiast • Twitter: @kingsleyadio
5. Java 9/8?
 Java EE/Spring?
 Android? About you
6. Why we Kotlin How we Kotlin Agenda
7. Our background
8. Our background • Java SE 6, EE 6 • Ant-based NetBeans project • No CI/CD, No cloud • SOA with ESB via SOAP
9. Why we Kotlin
10. Why we Kotlin Kotlin is concise K.I.S.S. Keep It Simple, Stupid
12. Why we Kotlin Kotlin is safe
13. Why we Kotlin Kotlin is developer-friendly and tool-friendly
14. Why we Kotlin Kotlin inter-ops nicely with Java
15. Why we Kotlin Kotlin is well supported
16. Why we Kotlin Kotlin is battle-tested in production
17. Why we Kotlin Kotlin has a large and thriving ecosystem
18. GitHub Stars Stars (thousands) 0 4.5 9 13.5 18 Ceylon Groovy Clojure Scala Kotlin
19. Community 12,000 members 22,000 followers 5,000 questions 5,800 readers
20. Why we Kotlin Kotlin adds no overhead
21. Artifact Size Kilobytes 0 1500 3000 4500 6000 Groovy (v2.4.12) Clojure (v1.8.0) Scala (v2.12.3) Kotlin (v1.1.50)
22. Method Count Methods 0 15000 30000 45000 60000 Groovy (v2.4.12) Clojure (v1.8.0) Scala (v2.12.3) Kotlin (v1.1.50) 6,315 50,794 16,023 28,866
23. Why we Kotlin Kotlin addresses many of Java’s legacy problems and offers a modern perspective
24. How we Kotlin
25. How we Kotlin Acknowledge that Kotlin is not just “pretty Java”
26. How we Kotlin Simply add Kotlin 
 to your build chain
27. Maven
28. Maven
29. Android Studio
30. Gradle
31. How we Kotlin Cmd + Opt + Shift + K
32. Cmd + Opt + Shift + K • GCM client’s Message.java (299 lines) • After conversion in IDEA (259 lines) • After hand-tuning (25 lines) https://goo.gl/u4dvNC
33. Message.kt
34. How we Kotlin Convert entities and DTOs
35. How we Kotlin Convert tests
36. Vaadin TestBench
37. How we Kotlin Convert core business beans, only if you make significant changes to them
38. How we Kotlin Open up EJB and CDI beans
39. Open up CDI beans
40. How we Kotlin Don’t take Kotlin’s terseness as a license to write cryptic code!
42. How we Kotlin Take full advantage of the language, especially the type system
43. How we Kotlin • It’s okay to write Java-like Kotlin in the beginning. • It’s awesome to write idiomatic Kotlin as you evolve.
44. How we Kotlin When in doubt, inspect the bytecode
45. Inspect bytecode
46. How we Kotlin If you don’t understand bytecode, view it as decompiled Java
47. Decompile bytecode
48. Attention!
49. Attention Limited static analysis tools
50. Attention Vararg parameter of type T following a parameter of type T
51. Java Varargs public Stuff doStuff(int start, int... steps) {
 // Do some stuff.
 } public Stuff doStuff(int start, int[] steps) {
 // Do some stuff.
 }
52. Attention Default parameter value in JAX-RS endpoints? Nope.
53. JAX-RS default @GET
 @JvmOverloads
 fun getPhone(@QueryParam(“name”) name: String = “iPhone”)
 = em.find<Phone>(name) @GET
 fun getPhone(@QueryParam(“name”) 
 @DefaultValue(“iPhone”) name: String)
 = em.find<Phone>(name)
54. Attention Kotlin singleton as CDI/EJB singleton? Nope.
55. CDI/EJB singletons @Singleton
 object MyBean {
 // Bean members.
 } @Singleton
 class MyBean {
 // Bean members.
 }
56. Attention Kotlin data classes as JPA entities? Nope.
57. JPA entities @Entity
 data class MyEntity {
 // Entity members.
 } @Entity
 class MyEntity {
 // Entity members.
 }
58. Attention Javadoc Documentation
59. Documentation
60. Attention Reserved words used by testing frameworks like Mockito and TestBench
61. Reserved words private inline fun <reified T : AbstractElement> select() = `$`(T::class.java) select<ButtonElement>().caption("Submit").first().click()
62. Attention Lazy delegate and Android views
63. Lazy delegate private val myTextView: TextView by lazy { findViewById(R.id.my_text_view) } LazyThreadSafety.SYNCHRONIZED LazyThreadSafety.PUBLICATION LazyThreadSafety.NONE
64. Lazy delegate • Butterknife • Android extensions • Data-binding • Anko
65. Attention Annotation processing
66. Annotation processing annotationProcessor 
 “com.google.dagger:dagger-compiler:$daggerVersion” apply plugin: ‘kotlin-kapt'
 ...
 kapt “com.google.dagger:dagger-compiler:$daggerVersion”
67. Notes
68. Notes Kotlin is not perfect
69. Notes Kotlin offers great compatibility guarantees
70. Notes We can help report bugs. Quick hotfix updates come between patch releases https://kotl.in/issue
71. Conclusion
72. Useful links https://kotlinlang.org https://kotlin.link https://kotlin.slack.com https://developer.android.com/kotlin/get-started.html https://goo.gl/7Dwuh7
73. Happy Kotlin :)