Micronaut Microservices Framework: Introduction

Micronaut supports Java, Groovy, and Kotlin as first-class citizens. Let us create a new Java application using Micronaut CLI:

This will scaffold a new Gradle project. If you prefer Maven, add a --build maven parameter. If you want to create a new Groovy or Kotlin project, add a --lang parameter:

By default Micronaut HTTP server will listen on a random port, but you can alter that by adding the following configuration to src/main/resources/application.yml:

The application can be immediately run with Gradle:

Now we can check that Micronaut is running:

To run the application with IntelliJ IDEA, you need to enable annotation processing:

1. open Settings / Build, Execution, Deployment / Compiler / Annotation Processors

2. Set the checkbox “Enable annotation processing”

Then you can run the application by executing the application class in IDEA.

Let us use the CLI again to create an HTTP controller. Run this command in the directory of the project that we created:

As we can see, Micronaut cares about Test-Driven Development and has created a test along with the controller:

Micronaut provides a great declarative compile-time HTTP client. You can use it for testing your own server (as we will do in the next example) or for communicating with external servers.

Here is what Micronaut creates:

That is all of it – only the interface. Micronaut will generate the implementation at compile time.

1package mn.hello.java;
2 
3import io.micronaut.http.annotation.Get;
4import io.micronaut.http.annotation.QueryValue;
5 
6public interface HelloApi {
7 
8    @Get("/")
9    HelloMessage index(@QueryValue("name") String name);
10}

1package mn.hello.java;
2 
3public class HelloMessage {
4    public String greeting;
5}

1package mn.hello.java;
2 
3import io.micronaut.http.annotation.Controller;
4 
5@Controller("/hello")
6public class HelloController implements HelloApi {
7 
8    @Override
9    public HelloMessage index(String name) {
10        HelloMessage m = new HelloMessage();
11        m.greeting = "Hello " + name + "!";
12        return m;
13    }
14}

1package mn.hello.java;
2 
3import io.micronaut.http.client.Client;
4 
5@Client("/hello")
6public interface HelloClient extends HelloApi {}

1package mn.hello.java;
2 
3import io.micronaut.context.ApplicationContext;
4import io.micronaut.runtime.server.EmbeddedServer;
5import org.junit.Test;
6 
7import static org.junit.Assert.assertEquals;
8 
9public class HelloControllerTest {
10 
11    @Test
12    public void testIndex() throws Exception {
13        EmbeddedServer server = ApplicationContext.run(EmbeddedServer.class);
14 
15        HelloClient client = server.getApplicationContext().getBean(HelloClient.class);
16 
17        HelloMessage serverResponse = client.index("codecentric");
18 
19        assertEquals("Hello codecentric!", serverResponse.greeting);
20        server.stop();
21    }
22}