Launch a Java REST API with Micronaut

In this tutorial, I’ll show you how to create a secure REST API and native image with Micronaut. You’ll see how to run a secure, OAuth 2.0-protected, Java REST API that allows JWT authentication. Then, I’ll compare its performance with Quarkus, Spring Boot, and Helidon.

This tutorial is also available as a screencast.

Prerequisites:

The brackets at the end of some steps indicate the IntelliJ Live Templates I used in the video. You can find the template definitions at mraible/idea-live-templates.

Install a JDK with GraalVM

Use SDKMAN to install Java 17 with GraalVM

sdk install java 22.1.0.r17-grl

Generate an OAuth 2.0 access token

  1. Install the Okta CLI and run okta register to sign up for a new account. If you already have an account, run okta login.

  2. Run okta apps create spa. Set oidcdebugger as an app name and press Enter.

  3. Use https://oidcdebugger.com/debug for the Redirect URI and set the Logout Redirect URI to https://oidcdebugger.com.

  4. Navigate to the OpenID Connect Debugger website.

    1. Fill in your client ID

    2. Use https://{yourOktaDomain}/oauth2/default/v1/authorize for the Authorize URI

    3. Select code for the response type and Use PKCE

    4. Click Send Request to continue

  5. Set the access token as a TOKEN environment variable in a terminal window.

    TOKEN=eyJraWQiOiJYa2pXdjMzTDRBYU1ZSzNGM...

Make a Micronaut Java REST API

  1. Use SDKMAN to install Micronaut’s CLI and create an app:

    sdk install micronaut
    mn create-app com.okta.rest.app --build maven -f security-jwt -f micronaut-aot
    mv app micronaut
  2. Create controller/HelloController.java: [mn-hello]

    package com.okta.rest.controller;
    
    import io.micronaut.http.MediaType;
    import io.micronaut.http.annotation.Controller;
    import io.micronaut.http.annotation.Get;
    import io.micronaut.http.annotation.Produces;
    import io.micronaut.security.annotation.Secured;
    import io.micronaut.security.rules.SecurityRule;
    
    import java.security.Principal;
    
    @Controller("/hello")
    public class HelloController {
    
        @Get
        @Secured(SecurityRule.IS_AUTHENTICATED)
        @Produces(MediaType.TEXT_PLAIN)
        public String hello(Principal principal) {
            return "Hello, " + principal.getName() + "!";
        }
    
    }
  3. Enable and configure JWT security in src/main/resources/application.yml: [mn-security-config]

    micronaut:
      ...
      security:
        enabled: true
        token:
          jwt:
            enabled: true
            claims-validators:
              issuer: https://{yourOktaDomain}/oauth2/default
            signatures:
              jwks:
                okta:
                  url: https://{yourOktaDomain}/oauth2/default/v1/keys

Run and test your Micronaut REST API with HTTPie

  1. Start your app:

    ./mvnw mn:run
  2. Use HTTPie to pass the JWT in as a bearer token in the Authorization header:

    http :8080/hello Authorization:"Bearer $TOKEN"

    You should get a 200 response with your email in it.

Build a Native Micronaut App

  1. Compile your Micronaut app into a native binary:

    ./mvnw clean package -Dpackaging=native-image
  2. Start your Micronaut app:

    ./target/app
  3. Test it with HTTPie and an access token:

    http :8080/hello Authorization:"Bearer $TOKEN"

Startup time comparison

I compared startup times between frameworks by running each image three times before recording the numbers. Then, I ran each app five more times and averaged the results. I gathered these numbers on a 2019 MacBook Pro with an SSD, 2.4 GHz 8-Core Intel Core i9 processor, and 64 GB of RAM.

Versions used: Quarkus 2.9.0, Micronaut 3.4.3, Helidon 2.5.0, and Spring Boot 2.6.7 with Spring Native 0.11.5.

Memory usage comparison

I tested the memory usage (in megabytes) of each app using the command below. I ran it right after I started the app, after a single authenticated request, and after five authenticated requests.

ps -o pid,rss,command | grep --color <executable> | awk '{$2=int($2/1024)"M";}{ print;}'

The chart below shows the memory usage after five requests.

What about the MacBook Pro M1 Max?

My MacBook Pro (16-inch, 2021) with Apple M1 Max builds much faster, apps start up 2x faster, but they use more memory.

Comparing Native Java REST API Frameworks Live Stream

I missed Devoxx France this year, but I’m still doing my presentation! I’ll be live-streaming Comparing Native Java REST API Frameworks on June 7, 2022 at 6:00 MDT (14:00 CEST). Join me or watch the recorded version below!

Secure Native Java with Micronaut FTW!

⚡️ Create a secure REST API with Micronaut: okta start micronaut

🚀 Find this example’s code on GitHub: @oktadev/native-java-examples/micronaut

Matt Raible is a well-known figure in the Java community and has been building web applications for most of his adult life. For over 20 years, he has helped developers learn and adopt open source frameworks and use them effectively. He's a web developer, Java Champion, and Developer Advocate at Okta. Matt has been a speaker at many conferences worldwide, including Devnexus, Devoxx Belgium, Devoxx France, Jfokus, and JavaOne. He is the author of The Angular Mini-Book, The JHipster Mini-Book, Spring Live, and contributed to Pro JSP. He is frequent contributor to open source and a member of the JHipster development team. You can find him online @mraible and raibledesigns.com.

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