Hello World: Your First Endpoint in Micronaut

When learning any new framework, it always starts with building your first “Hello World” application. In Micronaut, this is incredibly simple, but also very powerful because you start using its key features like:

Controllers
Routing
Dependency Injection
Auto-generated boilerplate

In this post, you’ll learn how to create your first endpoint in Micronaut step-by-step using very simple language — even if you’re completely new to Micronaut or web development.

What is an Endpoint in Micronaut?

In simple words:

An endpoint is a URL path that your application listens to. When someone visits that path, your application returns a response.

Example:

You visit: http://localhost:8080/hello
You get response: Hello, World!

That’s what we are going to build.

Go through Installing Micronaut CLI and Setting Up Your First Project for setting up the micronaut env.

Step 1 — Create Your Micronaut Project

We will use Micronaut CLI to create the project:

mn create-app com.kscodes.micronaut.helloworld --build=maven --lang=java

Explanation:

com.kscodes.micronaut.helloworld: This is the package name.
--build=maven: We are using Maven.
--lang=java: We are using Java.

✅ After running this, Micronaut will automatically create a full project structure for you.

Step 2 — Understand Where to Write Code

Inside the generated project, navigate to:

src/main/java/com/kscodes/micronaut/helloworld/

This is where we will add our code.

You will already see a file Application.java which looks like this:

package com.kscodes.micronaut.helloworld;

import io.micronaut.runtime.Micronaut;

public class Application {

public static void main(String[] args) {

Micronaut.run(Application.class, args);

}

This is your application’s entry point — Micronaut automatically starts the application from here.

Step 3 — Create Your First Controller

A controller is where you define endpoints.

Create a new Java file:

HelloController.java

Code:

package com.kscodes.micronaut.helloworld;

import io.micronaut.http.annotation.Controller;

import io.micronaut.http.annotation.Get;

@Controller("/hello")

public class HelloController {

@Get("/")

public String sayHello() {

return "Hello, World!";

}

Explanation (in very simple words):

Annotation	Meaning
`@Controller("/hello")`	This class handles requests that start with `/hello`.
`@Get("/")`	This method handles GET requests sent to `/hello/`.
`sayHello()`	The method returns the text `"Hello, World!"`.

✅ So when someone visits http://localhost:8080/hello/, they will see:
Hello, World!

Step 4 — Run Your Application

Use the following command to start the server:

mvnw mn:run

Micronaut will start your application and listen on port 8080 by default.

You should see something like:

Step 5 — Test Your Endpoint

Open your browser or use a tool like Postman or curl.

URL:

http://localhost:8080/hello/

Expected Output:

Hello, World!

🎉 Congratulations! You just built and ran your first Micronaut endpoint.

Step 6 — Customize the Endpoint

You can modify the controller to make it even more dynamic.

Updated Code:

package com.kscodes.micronaut.helloworld;

import io.micronaut.http.annotation.Controller;

import io.micronaut.http.annotation.Get;

import io.micronaut.http.annotation.PathVariable;

@Controller("/hello")

public class HelloController {

@Get("/{name}")

public String sayHello(@PathVariable String name) {

return "Hello, " + name + "!";

}

Now if you visit:

http://localhost:8080/hello/KSCodes

You’ll see:

Hello, KSCodes!

✅ You have now built a dynamic endpoint using path variables.

Quick Recap

Task	What You Learned
Create Project	Using Micronaut CLI
Controller	Handling requests with annotations
Endpoint	Return simple text responses
Dynamic Input	Use of path variables

Conclusion

Micronaut makes it super easy to build REST APIs and microservices, even for absolute beginners. With just a few lines of code, you have created a fully functional web service that responds to HTTP requests.

In upcoming tutorials, you can explore:

Handling query parameters
Returning JSON responses
Adding database connections
Securing your endpoints
Testing your application

Reference : Micronaut Docs