Plugins and Dependencies for Running Spring in Kotlin

Gradle Kotlin DSL Configuration #

We need to configure a build tool to manage the project.

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
    kotlin("jvm") version "1.4.32"
    kotlin("plugin.spring") version "1.4.32"
    id("org.springframework.boot") version "2.4.5"
    id("io.spring.dependency-management") version "1.0.11.RELEASE"
}

group = "personal.project"
version = "0.0.1-SNAPSHOT"
java.sourceCompatibility = JavaVersion.VERSION_11

repositories {
    mavenCentral()
}

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
    testImplementation("org.springframework.boot:spring-boot-starter-test")
}

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf("-Xjsr305=strict")
        jvmTarget = "1.8"
    }
}

tasks.withType<Test> {
    useJUnitPlatf

Plugins #

Let's look at the plugins required to run Spring in Kotlin.

Plugin? A group of pre-configured tasks that include essential information needed during a specific build process, and can be customized as needed.

plugins {
    kotlin("jvm") version "1.4.32"
    kotlin("plugin.spring") version "1.4.32"
    id("org.springframework.boot") version "2.4.5"
    id("io.spring.dependency-management") version "1.0.11.RELEASE"
}

First, there are kotlin(...) and id(...).

kotlin(...) is an abbreviation for Kotlin-specific IDs. Therefore, kotlin(...) can be expressed as id(...) and has the same meaning as id('org.jetbrains.kotlin.<...>').

kotlin("jvm") #

Kotlin is a multi-platform language.

You can check which platforms are supported on the official website's Supported platforms page.

In the project, we explicitly target the JVM.

kotlin("plugin.spring") #

This plugin is the allopen plugin.

By default, Kotlin classes are final, meaning inheritance is not possible unless the open keyword is explicitly used.

Spring AOP uses cglib, which employs the proxy pattern through inheritance.

Therefore, this plugin sets classes to be open by default.

id("org.springframework.boot") #

This is the plugin for using Spring Boot.

id("io.spring.dependency-management") #

This plugin is for managing versions of Spring-related dependencies uniformly.

Dependencies #

Let's take a look at the dependencies. I'll briefly explain the dependencies used when using Spring Boot in Java, and then discuss Kotlin-specific dependencies in more detail.

implementatiion("org.springframeworkboot:spring-boot-starter-web"): Dependency for using Spring Boot.

testImplementation("org.springframework.boot:spring-boot-starter-test"): Dependency for using Spring Boot tests.

implementation("org.jetbrains.kotlin:kotlin-reflect"): Kotlin does not provide reflection by default to reduce runtime library size, but adding this dependency allows you to use reflection.

implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8"): This library provides essential functionalities in Kotlin.

• Functions like let, apply, use, synchronized, etc.
• Extension functions that aid in using collections.
• Various utilities for string manipulation.
• Functions related to IO and Threading.

Main #

@SpringBootApplication
class Application

fun main(args: Array<String>) {
    runApplication<Application>(*args)
}

After the build tool configuration is complete, create a Kotlin class in src/main/kotlin/{package_name} and enter the following code.