Creating a microservice with Quarkus, Kotlin, and Gradle

This article is also available in Russian.

Preface

In the previous article, the brief explanations of creating microservices on the modern JVM frameworks and comparison of them were shown. Now it’s time to take a closer look at the most recently appeared framework: Quarkus. I’ll describe the process of creating a microservice using the mentioned technologies and in accordance with the requirements specified in the main article. This microservice will be a part of the following microservice architecture:

As usual, the project’s source code is available on GitHub.

Prerequisites

JDK 13
Consul

Creating an application from scratch

To generate a new project you can use a web starter or Maven (for Maven or Gradle project generation). It is worth noting that the framework supports Java, Kotlin, and Scala languages.

Dependencies

In this project, Gradle Kotlin DSL as a build tool is used. A build script should contain:

plugins
Listing 1. build.gradle.kts
```
plugins {
    kotlin("jvm")
    kotlin("plugin.allopen")
    id("io.quarkus")
}
```
Plugins' versions resolution is performed in settings.gradle.kts.

dependencies

Listing 2. build.gradle.kts

dependencies {
    ...
    implementation(enforcedPlatform("io.quarkus:quarkus-bom:$quarkusVersion"))
    implementation("io.quarkus:quarkus-resteasy-jackson")
    implementation("io.quarkus:quarkus-rest-client")
    implementation("io.quarkus:quarkus-kotlin")
    implementation("io.quarkus:quarkus-config-yaml")
    testImplementation("io.quarkus:quarkus-junit5")
    ...
}

More on importing Maven BOMs see in the Gradle docs.

Also, it is needed to make some Kotlin classes open (they’re final by default; more details on Gradle configuration in the Quarkus Kotlin guide):

Listing 3. build.gradle.kts

allOpen {
    annotation("javax.enterprise.context.ApplicationScoped")
}

Configuration

The framework supports configuration via properties or YAML files (more detailed in the Quarkus config guide).

The configuration file is located in the resources folder and looks like:

Listing 4. application.yaml

quarkus:
  http:
    host: localhost
    port: 8084

application-info:
  name: quarkus-service
  framework:
    name: Quarkus
    release-year: 2019

Here application’s standard properties are defined, as well as custom. Latter can be read as follows:

Listing 5. Reading properties (source code)

import io.quarkus.arc.config.ConfigProperties

@ConfigProperties(prefix = "application-info")
class ApplicationInfoProperties {

    lateinit var name: String

    lateinit var framework: FrameworkConfiguration

    class FrameworkConfiguration {
        lateinit var name: String
        lateinit var releaseYear: String
    }
}

Beans

Before we start with the coding part, it should be noted that there is no main method in the source code of your Quarkus application, but maybe somewhen it will be.

Injection of @ConfigProperties bean from the previous listing to another bean is performed using @Inject annotation:

Listing 6. Injection of @ConfigProperties bean (source code)

@ApplicationScoped
class ApplicationInfoService(
    @Inject private val applicationInfoProperties: ApplicationInfoProperties,
    @Inject private val serviceClient: ServiceClient
) {
    ...
}

ApplicationInfoService bean annotated with @ApplicationScoped can then be injected itself like this:

Listing 7. Injection of @ApplicationScoped bean (source code)

class ApplicationInfoResource(
    @Inject private val applicationInfoService: ApplicationInfoService
)

More on Contexts and Dependency Injection in the Quarkus CDI guide.

REST endpoints

REST controller looks very typical for those who are familiar with Spring or Java EE:

Listing 8. REST controller (source code)

@Path("/application-info")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
class ApplicationInfoResource(
    @Inject private val applicationInfoService: ApplicationInfoService
) {

    @GET
    fun get(@QueryParam("request-to") requestTo: String?): Response =
        Response.ok(applicationInfoService.get(requestTo)).build()

    @GET
    @Path("/logo")
    @Produces("image/png")
    fun logo(): Response = Response.ok(applicationInfoService.getLogo()).build()
}

REST client

For working in a microservice architecture Quarkus service should be able to perform requests to other services. Since every service has the same API, it is worth to create a uniform interface for common code, and then a bunch of REST clients extending that interface:

Listing 9. REST clients (source code)

@ApplicationScoped
@Path("/")
interface ExternalServiceClient {
    @GET
    @Path("/application-info")
    @Produces("application/json")
    fun getApplicationInfo(): ApplicationInfo
}

@RegisterRestClient(baseUri = "http://helidon-service")
interface HelidonServiceClient : ExternalServiceClient

@RegisterRestClient(baseUri = "http://ktor-service")
interface KtorServiceClient : ExternalServiceClient

@RegisterRestClient(baseUri = "http://micronaut-service")
interface MicronautServiceClient : ExternalServiceClient

@RegisterRestClient(baseUri = "http://quarkus-service")
interface QuarkusServiceClient : ExternalServiceClient

@RegisterRestClient(baseUri = "http://spring-boot-service")
interface SpringBootServiceClient : ExternalServiceClient

As you can see, creating REST clients to the other services is as simple as creating an interface using the proper JAX-RS and MicroProfile annotations.

Service Discovery

As you saw in the previous section for the baseUri parameter services' names are used. But now there is no built-in support of Service Discovery (Eureka) or it doesn’t work properly (Consul) because the framework mainly targets cloud environments. So I’ve implemented Service Discovery using Consul Client for Java library. Consul client includes two necessary functions, register and getServiceInstance (which uses the Round-robin algorithm):

Listing 10. Consul client (source code)

@ApplicationScoped
class ConsulClient(
    @ConfigProperty(name = "application-info.name")
    private val serviceName: String,
    @ConfigProperty(name = "quarkus.http.port")
    private val port: Int
) {

    private val consulUrl = "http://localhost:8500"
    private val consulClient by lazy {
        Consul.builder().withUrl(consulUrl).build()
    }
    private var serviceInstanceIndex: Int = 0

    fun register() {
        consulClient.agentClient().register(createConsulRegistration())
    }

    fun getServiceInstance(serviceName: String): Service {
        val serviceInstances = consulClient.healthClient().getHealthyServiceInstances(serviceName).response
        val selectedInstance = serviceInstances[serviceInstanceIndex]
        serviceInstanceIndex = (serviceInstanceIndex + 1) % serviceInstances.size
        return selectedInstance.service
    }

    private fun createConsulRegistration() = ImmutableRegistration.builder()
        .id("$serviceName-$port")
        .name(serviceName)
        .address("localhost")
        .port(port)
        .build()
}

At first, it is needed to register the application:

Listing 11. Registration in Consul (source code)

@ApplicationScoped
class ConsulRegistrationBean(
    @Inject private val consulClient: ConsulClient
) {

    fun onStart(@Observes event: StartupEvent) {
        consulClient.register()
    }
}

Then it is needed to resolve services' names to its particular location. For that, a class that extends ClientRequestFilter and annotated with @Provider was created:

Listing 12. Filter for working with Service Discovery (source code)

@Provider
@ApplicationScoped
class ConsulFilter(
    @Inject private val consulClient: ConsulClient
) : ClientRequestFilter {

    override fun filter(requestContext: ClientRequestContext) {
        val serviceName = requestContext.uri.host
        val serviceInstance = consulClient.getServiceInstance(serviceName)
        val newUri: URI = URIBuilder(URI.create(requestContext.uri.toString()))
            .setHost(serviceInstance.address)
            .setPort(serviceInstance.port)
            .build()

        requestContext.uri = newUri
    }
}

The resolution is implemented simply by replacement URI of requestContext object with a service’s location obtained from Consul client.

Testing

Tests for both API’s endpoints are implemented using REST Assured library:

Listing 13. Tests (source code)

@QuarkusTest
class QuarkusServiceApplicationTest {

    @Test
    fun testGet() {
        given()
            .`when`().get("/application-info")
            .then()
            .statusCode(200)
            .contentType(ContentType.JSON)
            .body("name") { `is`("quarkus-service") }
            .body("framework.name") { `is`("Quarkus") }
            .body("framework.releaseYear") { `is`(2019) }
    }

    @Test
    fun testGetLogo() {
        given()
            .`when`().get("/application-info/logo")
            .then()
            .statusCode(200)
            .contentType("image/png")
            .body(`is`(notNullValue()))
    }
}

While testing, it is not necessary to register application in Consul, so I just put ConsulClientMock that extends actual ConsulClient next to the test class:

Listing 14. Mock for ConsulClient (source code)

@Mock
@ApplicationScoped
class ConsulClientMock : ConsulClient("", 0) {

    // do nothing
    override fun register() {
    }
}

Building

During build Gradle task quarkusBuild task is being called. By default, it generates runner JAR and lib directory with all the dependencies. To produce uber-JAR artifact quarkusBuild task needs to be configured as follows:

Listing 15. Setting up the generation of uber-JAR (source code)

tasks {
    withType<QuarkusBuild> {
        isUberJar = true
    }
}

To build project run ./gradlew clean build in the project’s root folder.

Launch

Before launching the microservice, you need to start Consul (described in the main article).

You can start microservices:

using quarkusDev Gradle task

Execute in the project’s root folder:

./gradlew :quarkus-service:quarkusDev

or call the task from IDE
using the uber-JAR

Execute in the project’s root folder:

java -jar quarkus-service/build/quarkus-service-1.0.0-runner.jar

Now you can use REST API, for example, perform the following request:

GET http://localhost:8084/application-info

It will return:

Listing 16. API’s response

{
  "name": "quarkus-service",
  "framework": {
    "name": "Quarkus",
    "releaseYear": 2019
  },
  "requestedService": null
}

Spring compatibility

The framework provides compatibility layers for several Spring technologies: DI, Web, Security, Data JPA.

Conclusion

In this article, we saw how to implement a simple REST service on Quarkus using Kotlin and Gradle. If you look at the main article, you’ll see that created application has comparable parameters to the applications on the other new JVM frameworks. So the framework has serious competitors such as Helidon MicroProfile, Micronaut, and Spring Boot (if we speak about fullstack frameworks). Therefore I think that we are waiting for an interesting development of events that will be useful for the whole Java ecosystem.

Useful links

P.S. Thanks to vlsi for helping with this article.