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
   

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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
   

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3. ARRIVAL Robotics
   a web app to connect
   mechanical designers
   and robofacturing
   collecting
   real-time feedback
   software defined
   robofacturing
   Kotlin ?:
   earlier TRA Robotics
   

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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
   

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5. What Δ do you expect?
   

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6. code is shorter
   more expressive
   have fun doing the migration
   less routine coding
   faster feature creation
   better code reading
   language features and stdlib
   

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7. Minuses?
   

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8. Minuses?
   yes :(
   

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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
   

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10. Current State
    

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13. Code Style
    

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15. https://kotlinlang.org/docs/reference/code-style-migration-guide.html
    1 Oct. 2018
    Kotlin Coding Conventions
    

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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:
    
    official
    
    pom.xml
    kotlin.code.style=official
    gradle.properties
    

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17. Checkstyle
    

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18. https://github.com/arturbosch/detekt
    https://github.com/pinterest/ktlint
    

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19. Java 8 + Lombok -> Kotlin
    

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20. Equivalents
    @Getters
    @Setters
    properties
    @NonNull nullability
    @SneakyThrows only unchecked exceptions
    @Cleanup .use { … }
    val/var val/var
    @*ArgsConstructor primary constructor
    

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21. Equivalents
    @Getters
    @Setters
    properties
    @NonNull nullability
    @SneakyThrows only unchecked exceptions
    @Cleanup .use { … }
    val/var val/var
    @*ArgsConstructor primary constructor
    

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22. Equivalents
    @Getters
    @Setters
    properties
    @NonNull nullability
    @SneakyThrows only unchecked exceptions
    @Cleanup .use { … }
    val/var val/var
    @*ArgsConstructor primary constructor
    

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23. Equivalents
    @Getters
    @Setters
    properties
    @NonNull nullability
    @SneakyThrows only unchecked exceptions
    @Cleanup .use { … }
    val/var val/var
    @*ArgsConstructor primary constructor
    

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24. Equivalents
    @Getters
    @Setters
    properties
    @NonNull nullability
    @SneakyThrows only unchecked exceptions
    @Cleanup .use { … }
    val/var val/var
    @*ArgsConstructor primary constructor
    

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25. Equivalents
    @Getters
    @Setters
    properties
    @NonNull nullability
    @SneakyThrows only unchecked exceptions
    @Cleanup .use { … }
    val/var val/var
    @*ArgsConstructor primary constructor
    

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26. Complete Manual Implementation
    @ToString @EqualsAndHashCode
    @Synchronized @Builder
    

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27. @Data != data class
    

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28. Nullability
    

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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
    

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30. @Log
    val slf4j: ReadOnlyProperty
    get() = LoggerDelegate()
    class LoggerDelegate : ReadOnlyProperty {
    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
    

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31. @Log
    val slf4j: ReadOnlyProperty
    get() = LoggerDelegate()
    class LoggerDelegate : ReadOnlyProperty {
    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
    

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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”)
    }
    }
    

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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”)
    }
    }
    

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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
    

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35. @Log
    val slf4j: ReadOnlyProperty
    get() = LoggerDelegate()
    class LoggerDelegate : ReadOnlyProperty {
    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
    

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36. @Log
    val slf4j: ReadOnlyProperty
    get() = LoggerDelegate()
    class LoggerDelegate : ReadOnlyProperty {
    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
    

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37. Java to Kotlin Converter
    

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38. CTRL + ALT + SHIFT + K
    

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39. System.out.println(
    Integer.toHexString(
    0xFF000000
    )
    )
    FF000000
    0
    Compile error
    

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40. FF000000
    0
    Compile error
    System.out.println(
    Integer.toHexString(
    0xFF000000
    )
    )
    

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41. println(
    Integer.toHexString(
    -0x1000000
    )
    )
    Java to Kotlin Converter
    

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42. println(
    Integer.toHexString(
    0xFF000000
    )
    )
    FF000000
    0
    Compile error
    Rewritten
    

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43. FF000000
    0
    Compile error
    println(
    Integer.toHexString(
    0xFF000000
    )
    )
    Rewritten
    

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44. FF000000
    0
    Compile error
    println(
    Integer.toHexString(
    0xFF000000
    )
    )
    Rewritten
    Long
    https://discuss.kotlinlang.org/t/when-does-bit-fiddling-come-to-kotlin/2249
    

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45. FF000000
    0
    Compile error
    println(
    Integer.toHexString(
    0xFF000000.toInt()
    )
    )
    Rewritten
    workaround
    

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46. FF000000
    0
    Compile error
    println(
    Integer.toHexString(
    0xFF000000u.toInt()
    )
    )
    Rewritten
    experimental workaround
    

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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
    

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48. Before we start
    

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49. No tests - No migrations
    at least cover your core functionality
    

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50. Keep semantics
    

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51. Let’s do it
    

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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"
    }
    

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53. No Code - No Problems
    

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54. Repository
    let’s do that
    

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55. @JvmDefault
    

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56. compileKotlin {
    kotlinOptions {
    freeCompilerArgs = ["-Xjvm-default=compatibility"]
    jvmTarget = "1.8"
    }
    }
    https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.jvm/-jvm-default/index.html
    

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57. First migrations as small as possible
    but not smaller than a class
    the 1st avice
    

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58. Constants
    let’s do that
    

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59. @JvmField
    const val
    @file:JvmName(“...”)
    object … {
    ...
    }
    

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60. Keep backward compatibility
    even inside your team
    the 2nd advice
    

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61. Configs & Props
    let’s do that
    

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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
    

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63. First of all check docs
    docs of many libs/tools have a chapter called “Kotlin”
    the 3rd advice
    

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64. Aspects
    let’s do that
    

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65. The Converter Is Software
    can have bugs
    the 4rd advice
    

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66. Model
    let’s do that
    

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67. DTO & mappers
    let’s do that
    

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68. Check compatibility of your libs with Kotlin
    before migration!
    the 5th advice
    

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69. Be strong. Someday it will end
    probably not this month
    the 6th advice
    

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70. Services
    let’s do that
    

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71. Improve your code
    if changes are small but profit is great
    the 7rd advice
    

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72. Controllers
    let’s do that
    

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73. Check auto-generated* stuff manually
    if you are too lazy to write tests for it
    the 8th advice
    * not only, but at least
    

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74. Global Steps
    1. What Δ do you expect?
    2. Code Style / Checkstyle
    3. Migrate
    4. Review
    

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75. Global Steps
    1. What Δ do you expect?
    2. Code Style / Checkstyle
    3. Migrate
    4. Review
    

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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
    

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77. Go in small steps
    if you really ready to solve problems
    the final avice
    

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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
    

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