Kotlin learning pathway

kotlin.md

Language fluency

Interactive courses

• Kotlin crash course for programmers
• Kotlin koans

Projects

• Exercism
  • Dominoes
  • Bank Account
  • Forth
• Hyperskill projects
  • Kotlin basics track
  • Kotlin developer track
• Google's kotlin course

Other resources

• Idioms
• Community
• Kotlin standard library safari videos

Deep dives

• Coroutines book

Learning path

flowchart TD
    DataTypes("Kotlin types and collections")
    Null("Null safety")
    Expressions("Control structures and expressions")
    Functions("Functions and lambdas")
    Preconditions("require, check, assert")
    FP("Functional programming")
    Java("Interacting with Java code")
    OOP("Classes, data classes")
    ValueClasses("Value classes (inline classes)")
    Types("Type aliases, enums, sealed classes")
    Generics("Generics and variance")
    Packaging("Packages and imports")
    Destructuring("Destructuring")
    Coroutines("Coroutines")
    Ktor("Ktor")
    Serialization("Serialization")
    Test("kotlin.test")
    Text("kotlin.text")
    Time("kotlin.time")
    Reflection("Reflection API")
    JCA("Java Cryptography Architecture")
    IO("kotlin.io")
    DataTypes --> Null
    Null --> Expressions
    Expressions --> Functions
    Functions --> Preconditions
    Preconditions --> Destructuring
    Destructuring --> FP
    Destructuring --> OOP
    OOP --> Types
    OOP --> Generics
    FP --> Packaging
    Types --> Packaging
    Generics --> Packaging
    Packaging --> Test
    Test --> Text
    Test --> IO
    IO --> Time
    Time --> Java
    Time --> Serialization
    Time --> Coroutines
    Coroutines --> Ktor
    Java --> Reflection
    Java --> JCA
    OOP --> ValueClasses
    style DataTypes fill:#9f9,stroke:#333
    style Functions fill:#9f9,stroke:#333
    style Preconditions fill:#9f9,stroke:#333
    style Null fill:#9f9,stroke:#333
    style Expressions fill:#9f9,stroke:#333
    style IO fill:#9f9,stroke:#333
    style Test fill:#9f9,stroke:#333
    style OOP fill:#9f9,stroke:#333
    style ValueClasses fill:#9f9,stroke:#333
    style Couroutines fill:#9f9,stroke:#333
    style Types fill:#9f9,stroke:#333

Spring in Kotlin

Spring cheatsheet: https://dzone.com/refcardz/spring-configuration

Setting up a project

• https://spring.io/guides/tutorials/spring-boot-kotlin/
• Spring quick start series

Topics

• Transactions in spring
• Spring kotlin support
• Spring initializr
• Testing spring boot applications
• Hibernate and JPA and spring data
• Spring in action book

Learning path

flowchart TD
  Beans("Bean definition DSL")
  Configuration("Configuration")
  Injection("Dependency injection via annotations")
  SpringMVC("Spring MVC")
  JPA("SpringData, JPA")
  Flyway("Flyway migrations")
  Transactions("Transactions")
  Sagas("Saga pattern in Spring")
  Beans --> Injection
  Injection --> Configuration
  Configuration --> SpringMVC
  SpringMVC --> JPA
  JPA --> Flyway
  JPA --> Transactions
  Transactions --> Sagas
  style Flyway fill:#9f9,stroke:#333
  click Transactions href "https://victorrentea.teachable.com/p/transactions-in-spring" "Transactions course"

Dev tools and debugging tips

• Use https://play.kotlinlang.org/ for trying stuff out, and sharing for feedback
• If the project won't build properly...
  • Run a clean gradle build ./gradlew clean build
  • If dependencies changed, make sure to update the lockfile ./gradlew dependencies --write-locks
  • Idea should be configured to delegate to gradle for build and test
  • Use refresh button in gradle toolbar in Idea
  • https://www.jetbrains.com/help/idea/invalidate-caches.html
• Use https://sdkman.io as jdk version manager
• https://www.jpa-buddy.com/
• Kdoc is the equivalent of javadoc https://kotlinlang.org/docs/kotlin-doc.html

Build and run CLI apps with gradle

See https://www.baeldung.com/kotlin/gradle-executable-jar

tasks {
    val fatJar = register<Jar>("fatJar") {
        dependsOn.addAll(listOf("compileJava", "compileKotlin", "processResources")) // We need this for Gradle optimization to work
        archiveClassifier.set("standalone") // Naming the jar
        duplicatesStrategy = DuplicatesStrategy.EXCLUDE
        manifest { attributes(mapOf("Main-Class" to application.mainClass)) } // Provided we set it up in the application plugin configuration
        val sourcesMain = sourceSets.main.get()
        val contents = configurations.runtimeClasspath.get()
            .map { if (it.isDirectory) it else zipTree(it) } +
                sourcesMain.output
        from(contents)
    }
    build {
        dependsOn(fatJar) // Trigger fat jar creation during build
    }
}