Иван Осипов — Из Java на Kotlin, сидя на корме веб-приложения

Kotlin имеет место не только на поприще android разработки, но и в backend мире. Много кода уже написано на Java и Spring Boot, что же со всем этим делать?

Мигрировать! В ходе доклада мы проделаем путь с прекрасного "острова Java" со своими дикими зверьми вроде lombok в направлении "острова Kotlin", где постараемся адаптироваться и оглянуться назад.

Шаг за шагом мы мигрируем веб приложение с одного языка на другой, а по пути взглянем на местами неочевидные проблемы.

Transcript

1. From Java to Kotlin sitting aft on a web app
2. github.com/ivan-osipov/repository telegram ivan_osipov twitter _osipov_ name Ivan Osipov viber > sudo rm -rf whatsapp > dev/null deprecated i-osipov.ru t.me/from_junior_to_senior from-java-to-kotlin
3. ARRIVAL Robotics a web app to connect mechanical designers and robofacturing collecting real-time feedback software defined robofacturing Kotlin ?: earlier TRA Robotics
4. Agenda 1. Motivation 2. Preparation (checkstyle, autoformatting, test coverage) 3. Java + Lombok vs. Kotlin 4. Java to Kotlin Converter 5. Bugs, rakes and steps to migrate
5. What Δ do you expect?
6. code is shorter more expressive have fun doing the migration less routine coding faster feature creation better code reading language features and stdlib
7. Minuses?
8. Minuses? yes :(
9. lost ternary operator lost a number of ide features structural search, AspectJ highlights nullability noize!! lost implicit widening conversions companion object { noise } third party idiomaticity
10. Current State
13. Code Style
15. https://kotlinlang.org/docs/reference/code-style-migration-guide.html 1 Oct. 2018 Kotlin Coding Conventions
16. https://kotlinlang.org/docs/reference/code-style-migration-guide.html 1 Oct. 2018 Kotlin Coding Conventions • Since Kotlin 1.3 by default for new projects • For old projects: <properties> <kotlin.code.style>official</kotlin.code.style> </properties> pom.xml kotlin.code.style=official gradle.properties
17. Checkstyle
18. https://github.com/arturbosch/detekt https://github.com/pinterest/ktlint
19. Java 8 + Lombok -> Kotlin
20. Equivalents @Getters @Setters properties @NonNull nullability @SneakyThrows only unchecked exceptions @Cleanup .use { … } val/var val/var @*ArgsConstructor primary constructor
21. Equivalents @Getters @Setters properties @NonNull nullability @SneakyThrows only unchecked exceptions @Cleanup .use { … } val/var val/var @*ArgsConstructor primary constructor
22. Equivalents @Getters @Setters properties @NonNull nullability @SneakyThrows only unchecked exceptions @Cleanup .use { … } val/var val/var @*ArgsConstructor primary constructor
23. Equivalents @Getters @Setters properties @NonNull nullability @SneakyThrows only unchecked exceptions @Cleanup .use { … } val/var val/var @*ArgsConstructor primary constructor
24. Equivalents @Getters @Setters properties @NonNull nullability @SneakyThrows only unchecked exceptions @Cleanup .use { … } val/var val/var @*ArgsConstructor primary constructor
25. Equivalents @Getters @Setters properties @NonNull nullability @SneakyThrows only unchecked exceptions @Cleanup .use { … } val/var val/var @*ArgsConstructor primary constructor
26. Complete Manual Implementation @ToString @EqualsAndHashCode @Synchronized @Builder
27. @Data != data class
28. Nullability
29. @Log @Slf4j public class MyService { public void doSmth() { log.info(“my log entry”) } } class MyService { val log by slf4j fun doSmth() { log.info(“my log entry”) } } https://discuss.kotlinlang.org/t/best-practices-for-loggers/226/26
30. @Log val slf4j: ReadOnlyProperty<Any, Logger> get() = LoggerDelegate() class LoggerDelegate : ReadOnlyProperty<Any, Logger> { lateinit var logger: Logger override fun getValue(thisRef: Any, property: KProperty<*>): Logger { if (!::logger.isInitialized) logger = LoggerFactory.getLogger(thisRef.javaClass) return logger } } https://discuss.kotlinlang.org/t/best-practices-for-loggers/226/26
31. @Log val slf4j: ReadOnlyProperty<Any, Logger> get() = LoggerDelegate() class LoggerDelegate : ReadOnlyProperty<Any, Logger> { lateinit var logger: Logger override fun getValue(thisRef: Any, property: KProperty<*>): Logger { if (!::logger.isInitialized) logger = LoggerFactory.getLogger(thisRef.javaClass) return logger } } https://discuss.kotlinlang.org/t/best-practices-for-loggers/226/26
32. @Log @Slf4j public class MyService { public void doSmth() { log.info(“my log entry”) } } class MyService { val log by slf4j fun doSmth() { log.info(“my log entry”) } }
33. @Log @Slf4j public class MyService { public void doSmth() { log.info(“my log entry”) } } class MyService { companion object { val log by slf4j } fun doSmth() { log.info(“my log entry”) } }
34. @Log @Slf4j public class MyService { public void doSmth() { log.info(“my log entry”) } } class MyService { companion object { val log by slf4j } fun doSmth() { log.info(“my log entry”) } } https://www.reddit.com/r/Kotlin/comments/8gbiul/slf4j_loggers_in_3_ways INFO my.package.MyService$Companion - my log entry
35. @Log val slf4j: ReadOnlyProperty<Any, Logger> get() = LoggerDelegate() class LoggerDelegate : ReadOnlyProperty<Any, Logger> { lateinit var logger: Logger override fun getValue(thisRef: Any, property: KProperty<*>): Logger { if (!::logger.isInitialized) { val javaClass = thisRef.javaClass logger = LoggerFactory.getLogger( javaClass ) } return logger } } https://discuss.kotlinlang.org/t/best-practices-for-loggers/226/26
36. @Log val slf4j: ReadOnlyProperty<Any, Logger> get() = LoggerDelegate() class LoggerDelegate : ReadOnlyProperty<Any, Logger> { lateinit var logger: Logger override fun getValue(thisRef: Any, property: KProperty<*>): Logger { if (!::logger.isInitialized) { val javaClass = thisRef.javaClass logger = LoggerFactory.getLogger( if (javaClass.kotlin.isCompanion) javaClass.enclosingClass else javaClass ) } return logger } } https://discuss.kotlinlang.org/t/best-practices-for-loggers/226/26
37. Java to Kotlin Converter
38. CTRL + ALT + SHIFT + K
39. System.out.println( Integer.toHexString( 0xFF000000 ) ) FF000000 0 Compile error
40. FF000000 0 Compile error System.out.println( Integer.toHexString( 0xFF000000 ) )
41. println( Integer.toHexString( -0x1000000 ) ) Java to Kotlin Converter
42. println( Integer.toHexString( 0xFF000000 ) ) FF000000 0 Compile error Rewritten
43. FF000000 0 Compile error println( Integer.toHexString( 0xFF000000 ) ) Rewritten
44. FF000000 0 Compile error println( Integer.toHexString( 0xFF000000 ) ) Rewritten Long https://discuss.kotlinlang.org/t/when-does-bit-fiddling-come-to-kotlin/2249
45. FF000000 0 Compile error println( Integer.toHexString( 0xFF000000.toInt() ) ) Rewritten workaround
46. FF000000 0 Compile error println( Integer.toHexString( 0xFF000000u.toInt() ) ) Rewritten experimental workaround
47. FF000000 0 Compile error println( Integer.toHexString( 0xFF000000u ) ) Rewritten a future solution? https://discuss.kotlinlang.org/t/when-does-bit-fiddling-come-to-kotlin/2249
48. Before we start
49. No tests - No migrations at least cover your core functionality
50. Keep semantics
51. Let’s do it
52. Gradle Plugins plugins { ... id 'org.jetbrains.kotlin.jvm' version "1.3.50" id "org.jetbrains.kotlin.plugin.spring" version "1.3.50" id "org.jetbrains.kotlin.plugin.allopen" version "1.3.50" }
53. No Code - No Problems
54. Repository let’s do that
55. @JvmDefault
56. compileKotlin { kotlinOptions { freeCompilerArgs = ["-Xjvm-default=compatibility"] jvmTarget = "1.8" } } https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.jvm/-jvm-default/index.html
57. First migrations as small as possible but not smaller than a class the 1st avice
58. Constants let’s do that
59. @JvmField const val @file:JvmName(“...”) object … { ... }
60. Keep backward compatibility even inside your team the 2nd advice
61. Configs & Props let’s do that
62. https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html #boot-features-kotlin-configuration-properties @ConfigurationProperties when used in combination with @ConstructorBinding supports classes with immutable val properties since 2.2.0
63. First of all check docs docs of many libs/tools have a chapter called “Kotlin” the 3rd advice
64. Aspects let’s do that
65. The Converter Is Software can have bugs the 4rd advice
66. Model let’s do that
67. DTO & mappers let’s do that
68. Check compatibility of your libs with Kotlin before migration! the 5th advice
69. Be strong. Someday it will end probably not this month the 6th advice
70. Services let’s do that
71. Improve your code if changes are small but profit is great the 7rd advice
72. Controllers let’s do that
73. Check auto-generated* stuff manually if you are too lazy to write tests for it the 8th advice * not only, but at least
74. Global Steps 1. What Δ do you expect? 2. Code Style / Checkstyle 3. Migrate 4. Review
75. Global Steps 1. What Δ do you expect? 2. Code Style / Checkstyle 3. Migrate 4. Review
76. Migration Steps 1. Repositories 2. Constants 3. Config & Props 4. Delombok everything (at least one sub domain) 5. From the most abstract entity classes downwardly 6. Subdomains: Model + DTO + Mappers 7. Services & Another Domain Logic 8. Controllers
77. Go in small steps if you really ready to solve problems the final avice
78. github.com/ivan-osipov/repository telegram ivan_osipov twitter _osipov_ name Ivan Osipov viber > sudo rm -rf whatsapp > dev/null deprecated i-osipov.ru t.me/from_junior_to_senior from-java-to-kotlin