Native Image

This guide describes how to build a GraalVM native image for a Helidon MP application.

Introduction

Native images are ahead-of-time compiled Java code that result in a self contained native executable. When used appropriately native images have dramatically faster startup and lower runtime memory overhead compared to a Java VM.

In this guide you will learn how to build a native image locally on your machine, as well as using Docker.

What You Need

For this 10 minute tutorial, you will need the following:

Verify Prerequisites:

java -version
mvn --version
docker --version
kubectl version

Setting JAVA_HOME:

# On Mac
export JAVA_HOME=`/usr/libexec/java_home -v 21`

# On Linux
# Use the appropriate path to your JDK
export JAVA_HOME=/usr/lib/jvm/jdk-21

Install GraalVM and the Native Image Command

After downloading and installing GraalVM, set the GRAALVM_HOME environment variable to point at your GraalVM installation, or use the GraalVM installation as your Java home.

# Your path might be different
export GRAALVM_HOME=/usr/local/graalvm-jdk-21+35.1/Contents/Home/

Then verify:

$GRAALVM_HOME/bin/java -version
$GRAALVM_HOME/bin/native-image --version

Generate the Project

Generate the project using the Helidon MP Quickstart Maven archetype.

mvn -U archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion=4.4.0-SNAPSHOT \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp \
    -Dpackage=io.helidon.examples.quickstart.mp

The archetype generates a Maven project in your current directory (for example, helidon-quickstart-mp). Change into this directory and build.

cd helidon-quickstart-mp
mvn package

At this point you can run the application using the JVM:

java -jar target/helidon-quickstart-mp.jar

In another shell test an endpoint:

curl -X GET http://localhost:8080/greet

The application should respond with {"message":"Hello World!"}

Now stop the running application (by pressing Ctrl+C).

For more information about the Quickstart application and other endpoints it supports see the Helidon MP Quickstart Guide.

Building a Native Image

You can build a native executable in 2 different ways:

• With a local installation of GraalVM
• Using Docker

Local build

Make sure you have GraalVM locally installed:

$GRAALVM_HOME/bin/native-image --version

Build the native image using the native image profile:

mvn package -Pnative-image

Once it completes start the application using the native executable (no JVM!):

./target/helidon-quickstart-mp

Yep, it starts fast. You can exercise the application’s endpoints as before.

Multi-stage Docker build

Build the "native" Docker image

docker build -t helidon-quickstart-mp-native -f Dockerfile.native .

Start the application:

docker run --rm -p 8080:8080 helidon-quickstart-mp-native:latest

Again, it starts fast. You can exercise the application’s endpoints as before.

When should I use Native Images?

Native images are ideal for applications with high horizontal scalability requirements where the ability to rapidly scale out to numerous instances is important.

That said, native images do have some limitations, and for long running applications where startup and footprint are less of a priority, the Java SE HotSpot VM might be more appropriate.

For information about creating custom Java runtime images see Custom Runtime Images with jlink.