micronaut.md

Micronaut

Micronaut is a modern, JVM-based, fullstack framework for building modular, easily testable microservice and serverless applications. Micronaut provides a simple compile-time aspect-oriented programming API, which is very similar to Spring, but does not use reflection.

Build configuration

The integration with Micronaut is contained in the kvision-server-micronaut module. It has to be added as the dependency in the common target. This module depends on the micronaut-inject, micronaut-http, micronaut-router and micronaut-websocket. Any other dependencies can be added to build.gradle.kts and then be used in your application.

{% code title="build.gradle.kts" %}

dependencies {
    implementation(kotlin("reflect"))
    implementation("io.micronaut:micronaut-inject")
    implementation("io.micronaut.validation:micronaut-validation")
    implementation("io.micronaut.kotlin:micronaut-kotlin-runtime")
    implementation("io.micronaut:micronaut-runtime")
    implementation("io.micronaut:micronaut-http-server-netty")
    implementation("io.micronaut:micronaut-http-client")
    implementation("io.micronaut.session:micronaut-session")
    implementation("io.micronaut:micronaut-jackson-databind")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
    implementation("jakarta.validation:jakarta.validation-api")
    implementation("ch.qos.logback:logback-classic")
    implementation("org.yaml:snakeyaml")
}

{% endcode %}

Micronaut uses Kapt to generate code from various annotations in your application, so you need to configure Kapt:

{% code title="build.gradle.kts" %}

kapt {
    arguments {
        arg("micronaut.processing.incremental", true)
        arg("micronaut.processing.annotations", "com.example.*")
        arg("micronaut.processing.group", "com.example")
        arg("micronaut.processing.module", "template-fullstack-micronaut")
    }
}

dependencies {
    "kapt"(platform("io.micronaut.platform:micronaut-platform:$micronautVersion"))
    "kapt"("io.micronaut:micronaut-inject-java")
    "kapt"("io.micronaut.validation:micronaut-validation")
    "kaptTest"(platform("io.micronaut.platform:micronaut-platform:$micronautVersion"))
    "kaptTest"("io.micronaut:micronaut-inject-java")
}

{% endcode %}

Application configuration

The standard way to configure Micronaut application is src/jvmMain/resources/application.yml file. It contains options needed for optional dependencies. It can be empty if they are not used.

Implementation

Service class

The implementation of the service class comes down to implementing required interface methods and making it a Micronaut @Prototype component.

@Prototype
@Suppress("ACTUAL_WITHOUT_EXPECT")
actual class AddressService : IAddressService {
    override suspend fun getAddressList(search: String?, sort: Sort) {
        return listOf()
    }
    override suspend fun addAddress(address: Address) {
        return Address()
    }
    override suspend fun updateAddress(id: Int, address: Address) {
        return Address()
    }
    override suspend fun deleteAddress(id: Int) {
        return false
    }
}

Micronaut IoC (Inversion of Control) allows you to inject resources and other Micronaut components into your service class. You can use standard @Inject annotation or constructor based injection.

@Prototype
@Suppress("ACTUAL_WITHOUT_EXPECT")
actual class AddressService : IAddressService {
    @Inject
    lateinit var context: ApplicationContext

    override suspend fun getAddressList(search: String?, sort: Sort) {
        println(context.environment.activeNames)
        return listOf()
    }
    // ...
}

You can also inject custom Micronaut components, defined throughout your application.

KVision allows you to inject HttpRequest Micronaut object (which can also give you access to the user session, if it is configured)

@Prototype
@Suppress("ACTUAL_WITHOUT_EXPECT")
actual class AddressService : IAddressService {

    @Inject
    lateinit var httpRequest: HttpRequest<*>

    override suspend fun getAddressList(search: String?, sort: Sort) {
        println(httpRequest.uri)
        SessionForRequest.find(httpRequest).ifPresent { session ->
            println(session.id)    
        }
        return listOf()
    }
    // ...
}

{% hint style="info" %} Note: The new instance of the service class will be created by Micronaut for every server request. Use session or request objects to store your state with appropriate scope. {% endhint %}

Blocking code

Since Micronaut architecture is asynchronous and non-blocking, you should not block threads in your application code. If you have to use some blocking code (e.g. blocking I/O, JDBC) use the dedicated coroutine dispatcher.

@Prototype
@Suppress("ACTUAL_WITHOUT_EXPECT")
actual class AddressService : IAddressService {
    override suspend fun getAddressList(search: String?, sort: Sort) {
        return withContext(Dispatchers.IO) {
            retrieveAddressesFromDatabase(search, sort)
        }
    }
}

Application class

To allow KVision work with Micronaut you have to pass all instances of the KVServiceManager objects (defined in common code) to the Micronaut environment. You do this by defining a provider method for the KVManagers instance in the main application class.

@Factory
class KVApplication {
    @Bean
    fun getManagers() = KVManagers(listOf(getServiceManager<IAddressService>()))
}

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

Authentication

To secure your application you can use different Micronaut components and ready to use modules. See Micronaut Security guide for details. You can apply different security settings for different services by defining custom SecurityRule using KVision matches helper function.

import io.kvision.remote.matches

@Singleton
open class AppSecurityRule(rolesFinder: RolesFinder) : AbstractSecurityRule<HttpRequest<*>>(rolesFinder) {
    override fun check(request: HttpRequest<*>, authentication: Authentication?): Publisher<SecurityRuleResult> {
        return if (request.matches(getServiceManager<IAddressService>(), getServiceManager<IProfileService>())) {
            compareRoles(listOf(SecurityRule.IS_AUTHENTICATED), getRoles(authentication))
        } else {
            Mono.just(SecurityRuleResult.ALLOWED)
        }
    }
}