mn create-app example.micronaut.micronautguide --build=gradle --lang=groovy
Creating your first Micronaut app
Learn how to create a Hello World Micronaut app with a controller and a functional test.
Authors: Iván López, Sergio del Amo
Micronaut Version: 2.5.0
1. Getting Started
In this guide we are going to create a Micronaut app written in Groovy.
2. What you will need
To complete this guide, you will need the following:
-
Some time on your hands
-
A decent text editor or IDE
-
JDK 1.8 or greater installed with
JAVA_HOME
configured appropriately
3. Solution
We recommend that you follow the instructions in the next sections and create the app step by step. However, you can go right to the completed example.
-
Download and unzip the source
4. Writing the App
Create an app using the Micronaut Command Line Interface or with Micronaut Launch.
If you don’t specify the --build argument, Gradle is used as a build tool. If you don’t specify the --lang argument, Java is used as a language.
|
The previous command creates a Micronaut app with the default package example.micronaut
in a folder named micronautguide
.
4.1. Application
Application.groovy
is used when running the application via Gradle or via deployment. You can also run the main class directly within your IDE if it is configured correctly.
package example.micronaut
import io.micronaut.runtime.Micronaut
import groovy.transform.CompileStatic
@CompileStatic
class Application {
static void main(String[] args) {
Micronaut.run(Application, args)
}
}
4.2. Controller
In order to create a microservice that responds with "Hello World" you first need a controller.
Create a Controller:
package example.micronaut
import groovy.transform.CompileStatic
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Produces
import io.micronaut.http.MediaType
@CompileStatic
@Controller("/hello") (1)
class HelloController {
@Get("/") (2)
@Produces(MediaType.TEXT_PLAIN) (3)
String index() {
"Hello World" (4)
}
}
1 | The class is defined as a controller with the @Controller annotation mapped to the path /hello |
2 | The @Get annotation is used to map the index method to all requests that use an HTTP GET |
3 | By default a Micronaut’s response uses application/json as Content-Type . We are returning a String not a JSON object. Because of that, we set it to text/plain . |
4 | A String "Hello World" is returned as the result |
4.3. Test
Create a test which verifies that when you do a GET request to /hello
you get Hello World
as a response:
package example.micronaut
import io.micronaut.http.HttpRequest
import io.micronaut.http.client.RxHttpClient
import io.micronaut.http.client.annotation.Client
import io.micronaut.test.extensions.spock.annotation.MicronautTest
import spock.lang.Specification
import javax.inject.Inject
@MicronautTest (1)
class HelloControllerSpec extends Specification {
@Inject
@Client("/") (2)
RxHttpClient client
void "test hello world response"() {
when:
HttpRequest request = HttpRequest.GET('/hello') (3)
String rsp = client.toBlocking().retrieve(request)
then:
rsp == "Hello World"
}
}
1 | Annotate the class with @MicronautTest so Micronaut will initialize the application context and the embedded server. |
2 | Inject the RxHttpClient bean. It is used the execute an HTTP call to the controller. |
3 | Creating HTTP Requests is easy thanks to Micronaut’s fluid API. |
5. Testing the Application
To run the tests:
$ ./gradlew test
$ open build/reports/tests/test/index.html
6. Running the Application
To run the application use the ./gradlew run
command which will start the application on port 8080.
7. Next steps
Read more about Micronaut testing.
8. Help with Micronaut
Object Computing, Inc. (OCI) sponsored the creation of this Guide. A variety of consulting and support services are available.