Background

Spring Boot is a very popular framework for building microservices. Nowadays packaging a Spring Boot application as a Docker container is very common practice. In this blog post, we will see how we can create a Spring Boot application using GraalVM.

Example Code

This article is based on working code that you can find on GitHub.

Setting up the project

Let's create a simple Spring Boot application that returns a hello world message.

curl https://start.spring.io/starter.zip -d dependencies=web,devtools \
           -d bootVersion=3.0.2.RELEASE -o demo.zip

Now, let's unzip the file and import the project in your favorite IDE. Add the following code to the HelloWorldController.java file.

@RestController
public class HelloWorldController {
    @GetMapping("/hello")
    public Map<String, String> helloWorld() {
        return Map.of("message", "Hello World!");
    }
}

Creating a Docker image without GraalVM

Install jdk using sdkman.

sdk install java 19.0.2-open
sdk use java 19.0.2-open

Now, let's create a Docker image for this application using spring boot plugin.

./gradlew bootBuildImage --imageName=local.dev/example

Now, let's run the docker image and test it.

docker run --rm -p 8080:8080 local.dev/example
curl localhost:8080/hello

Create a Docker image using GraalVM

Install graalvm using sdkman.

sdk install java 22.3.r19-grl
sdk use java 22.3.r19-grl

Add graalvm plugin to the build.gradle file.

plugins {
    ...
    id 'org.graalvm.buildtools.native' version '0.9.17'
}

Use graalvm native compiler to compile the application and run as standalone application without using jre.

./gradlew nativeBuild
./build/native/nativeCompile/demo

Build the native image.

./gradlew bootBuildImage --imageName=local.dev/example-native

This will take some time to build the native image. Now, let's run the docker image and test it.

docker run --rm -p 8081:8080 local.dev/example
curl localhost:8081/hello

Conclusion

In this blog post, we saw how we can create a Spring Boot docker image using GraalVM.