Micronaut Kotlin

https://micronaut-projects.github.io/micronaut-kotlin/latest/guide
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Micronaut Kotlin provides extensions and integrations for building Kotlin applications with...
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### Define Ktor Routes with KtorRoutingBuilder in Kotlin

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

This example illustrates defining Ktor application routes using `io.micronaut.ktor.KtorRoutingBuilder`. It shows how to define GET and POST endpoints, handle incoming requests, and use dependency injection for services like `GreetingService`.

```kotlin
import io.ktor.server.application.call
import io.ktor.server.request.receive
import io.ktor.server.response.respond
import io.ktor.server.routing.*
import io.micronaut.ktor.KtorRoutingBuilder
import jakarta.inject.Singleton

@Singleton
class GreetingRoutes(private val greetingService: GreetingService) : KtorRoutingBuilder({
    get("/") {
        call.respond(greetingService.greet())
    }

    post("/") {
        val name = call.receive<CustomGreetingRequest>().name

        call.respond(greetingService.greet(name))
    }
})

data class CustomGreetingRequest(val name: String)
```

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### Start Micronaut Application with Kotlin

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

This code snippet shows how to start a Micronaut application using Kotlin. It configures the application to scan specific packages and map runtime exceptions to HTTP status codes.

```kotlin
object Application

fun main(args: Array<String>) {
    startApplication<Application>(*args) {
        packages("org.example.app")
        mapError<RuntimeException> { 500 }
    }
}
```

--------------------------------

### Example Micronaut Kotlin Application Configuration (application.conf)

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

Defines type-safe configuration for a Micronaut Kotlin application using Config4k and HOCON format. This example sets the server port and custom properties.

```hocon
micronaut {
  server {
    port = 8081
  }
}

test-property = "bad-value"

custom {
  user = ${USER}
}
```

--------------------------------

### Define Ktor Features with KtorApplicationBuilder in Kotlin

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

This snippet demonstrates how to define Ktor features by subclassing `io.micronaut.ktor.KtorApplicationBuilder`. It shows the installation of the `ContentNegotiation` feature and configuration of Jackson for JSON serialization.

```kotlin
import com.fasterxml.jackson.databind.SerializationFeature
import io.ktor.server.application.install
import io.ktor.server.plugins.contentnegotiation.ContentNegotiation
import io.ktor.serialization.jackson.jackson
import io.micronaut.ktor.KtorApplicationBuilder
import jakarta.inject.Singleton

@Singleton
class GreetingConfiguration : KtorApplicationBuilder({
    install(ContentNegotiation) {
        jackson {
            enable(SerializationFeature.INDENT_OUTPUT)
        }
    }
})
```

--------------------------------

### Micronaut Ktor Application Entry Point (Kotlin)

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

Demonstrates the entry point for a Micronaut Ktor application using the KtorApplication class. It configures the Ktor server, application engine, and includes a main method for running the application.

```kotlin
import io.ktor.server.netty.NettyApplicationEngine
import io.micronaut.ktor.KtorApplication
import io.micronaut.ktor.runApplication
import jakarta.inject.Singleton
import org.slf4j.LoggerFactory

@Singleton
class Application : KtorApplication<NettyApplicationEngine.Configuration>({
    applicationEngineEnvironment {
        log = LoggerFactory.getLogger(Application::class.java)
    }

    applicationEngine {
        workerGroupSize = 10
    }
})

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

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### Demonstrate HttpMessage Extension Usage in Kotlin

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

This snippet demonstrates the usage of HttpMessage extensions in Kotlin for accessing request and response bodies, including handling exceptional paths with custom exceptions. It utilizes Micronaut's client and argument mapping.

```kotlin
val exchangeOneConventionalBody: Hero? = exchangeOneConventional.body.getOrNull()
val exchangeOneReifiedBody: Hero? = exchangeOneReified.bodyOrNull

val exchangeOneConventionalCustomException: HttpClientResponseException = assertThrows<HttpClientResponseException> {
    client.exchange(HttpRequest.GET<Any>("/heroes/conflict"), Argument.of(Hero::class.java))
}
val exchangeOneReifiedCustomException: HttpClientResponseException = assertThrows<HttpClientResponseException> {
    client.exchangeObject<Hero>(HttpRequest.GET("/heroes/conflict"))
}
val exchangeOneConventionalCustomExceptionBody: HeroJsonError? = exchangeOneConventionalCustomException.response.getBody(HeroJsonError::class.java).getOrNull()
val exchangeOneReifiedCustomExceptionBody: HeroJsonError? = exchangeOneReifiedCustomException.response.getBodyObject<HeroJsonError>()
```

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### Demonstrate Reified Type Parameters for BlockingHttpClient in Kotlin

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

This code compares conventional and reified type parameter usage with Micronaut's `BlockingHttpClient` for both single and list responses. It highlights how reified types simplify client calls by removing the need for explicit `Argument` definitions.

```kotlin
// Compare exchange usage
val exchangeOneConventional: HttpResponse<Hero> = client.exchange(HttpRequest.GET<Any>("/heroes/any"), Argument.of(Hero::class.java))
val exchangeOneReified: HttpResponse<Hero> = client.exchangeObject<Hero>(HttpRequest.GET("/heroes/any"))

// Compare retrieve usage
val retrieveOneConventional: Hero = client.retrieve(HttpRequest.GET<Any>("/heroes/any"), Argument.of(Hero::class.java))
val retrieveOneReified: Hero = client.retrieveObject<Hero>(HttpRequest.GET("/heroes/any"))

// Compare exchange usage
val exchangeListConventional: HttpResponse<MutableList<Hero>> = client.exchange(HttpRequest.GET<Any>("/heroes/list"), Argument.listOf(Hero::class.java))
val exchangeListReified: HttpResponse<List<Hero>> = client.exchangeList<Hero>(HttpRequest.GET("/heroes/list"))

// Compare retrieve usage
val retrieveListConventional: MutableList<Hero> = client.retrieve(HttpRequest.GET<Any>("/heroes/list"), Argument.listOf(Hero::class.java))
val retrieveListReified: List<Hero> = client.retrieveList<Hero>(HttpRequest.GET("/heroes/list"))
```

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### Add Micronaut Ktor Dependency (Maven)

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

Adds the 'micronaut-ktor' dependency to your Maven project, allowing Ktor to be used as the server framework for your Micronaut applications.

```xml
<dependency>
    <groupId>io.micronaut.kotlin</groupId>
    <artifactId>micronaut-ktor</artifactId>
</dependency>
```

--------------------------------

### Add Micronaut Kotlin Extension Functions Dependency

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

This snippet shows how to add the `micronaut-kotlin-extension-functions` dependency to your project using Gradle and Maven. This dependency enhances the usability of Micronaut with Kotlin by providing convenient extension functions.

```gradle
implementation("io.micronaut.kotlin:micronaut-kotlin-extension-functions")
```

```maven
<dependency>
    <groupId>io.micronaut.kotlin</groupId>
    <artifactId>micronaut-kotlin-extension-functions</artifactId>
</dependency>
```

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### Add Micronaut Ktor Dependency (Gradle)

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

Integrates the 'micronaut-ktor' dependency into your Gradle build, enabling the use of Ktor as the server within a Micronaut application.

```gradle
implementation("io.micronaut.kotlin:micronaut-ktor")
```

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### Add Micronaut Kotlin Runtime Dependency (Maven)

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

Includes the 'micronaut-kotlin-runtime' dependency in your Maven project, which provides Config4k support and integrates 'jackson-module-kotlin' at runtime.

```xml
<dependency>
    <groupId>io.micronaut.kotlin</groupId>
    <artifactId>micronaut-kotlin-runtime</artifactId>
</dependency>
```

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### Add Micronaut Kotlin Runtime Dependency (Gradle)

Source: https://micronaut-projects.github.io/micronaut-kotlin/latest/guide/index

Adds the 'micronaut-kotlin-runtime' dependency to your Gradle build, enabling features like Config4k support and a runtime dependency on 'jackson-module-kotlin'.

```gradle
implementation("io.micronaut.kotlin:micronaut-kotlin-runtime")
```
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