Kotlin - Annotations

This tutorial lets you write a Kotlin application and use Koin inject and retrieve your components.

Get the code

info

The source code is available at on Github

Setup

Add KSP in your root Gradle config:

// Add KSP Plugin

plugins {

id "com.google.devtools.ksp" version "$ksp_version"

}

Check that the dependencies are added like below:

// Add Maven Central to your repositories if needed

repositories {

mavenCentral()

}

// Use KSP Plugin

apply plugin: 'com.google.devtools.ksp'

// Use KSP Generated sources

sourceSets.main {

java.srcDirs("build/generated/ksp/main/kotlin")

}

dependencies {

// Koin

compile "io.insert-koin:koin-core:$koin_version"

compile "io.insert-koin:koin-annotations:$koin_ksp_version"

ksp "io.insert-koin:koin-ksp-compiler:$koin_ksp_version"

}

The application

In our small app we need to have components, to make coffee:

• CoffeeApplication - run the coffee maker
• CoffeeMaker - run the coffee process, by using a Pump and a Heater
• ElectricHeater - a electric heater, to heat the water of the coffee
• Thermosiphon - a pump to pump the water when it's hot

Coffee Maker parts

Below are the components, declared as single instance with @Single annotation:

@Single

class ElectricHeater : Heater

@Single

class Thermosiphon(private val heater: Heater) : Pump

@Single

class CoffeeMaker(private val pump: Pump, private val heater: Heater)

The CoffeeApplication class

To "make our coffee", we need to create a runtime component. Let's write a CoffeeApplication class and tag it with KoinComponent interface. This will later allows us to use the by inject() functions to retrieve our component:

class CoffeeApplication : KoinComponent {

// retrieve CoffeeMaker

private val maker: CoffeeMaker by inject()

fun run(){

maker.brew()

}

}

Declaring a Module

We just need a module to scan all our components for the given package:

@Module

@ComponentScan("org.koin.sample.coffee")

class CoffeeAppModule

• @Module annotation declare the module class
• @ComponentScan annotation scan for components

That's it!

Just start our app from a main function:

fun main(vararg args: String) {

startKoin {

// load our module

modules(CoffeeAppModule().module)

}

// run coffee

CoffeeApplication().run()

}