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Java Native Image Buildpack

The Paketo Java Native Image Buildpack allows users to create an image containing a GraalVM native image application.

The Java Native Buildpack is a composite buildpack and each step in a build is handled by one of it’s components. The following docs describe common build configurations. For a full set of configuration options and capabilities see the homepages of the component buildpacks.

About the Examples

All Java Native Image Buildpack examples will use the Paketo sample applications.

Examples assume that the root of this repository is the working directory:

git clone https://github.com/paketo-buildpacks/samples
cd samples
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The pack CLI is used throughout the examples. pack is just one of several Cloud Native Buildpack platforms than can execute builds with the Java Native Image Buildpacks. For example, Spring Boot developers may want to explore the Spring Boot Maven Plugin or Spring Boot Gradle Plugin.

Examples assume that either the Paketo Tiny or Paketo Base builder is the default builder:

pack config default-builder paketobuildpacks/builder:tiny
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All java native image example images should return {"status":"UP"} from the [actuator health endpoint][spring boot actuator endpoints].

docker run --rm --tty --publish 8080:8080 samples/java-native
curl -s http://localhost:8080/actuator/health | jq .
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Supported Applications

For all native image builds, it is required that:

• BP_NATIVE_IMAGE is set at build time.

For Spring Boot applications, it is required that:

• The application declares a dependency on Spring Native.
• The version of Spring Native declared by the application may require a specific version of Spring Boot. See the Spring Native release notes for supported Spring Boot versions.

Building From Source

The Java Native Image Buildpack supports the same build tools and configuration options as the Java Buildpack. The build must produce an executable jar.

After compiling and packaging, the buildpack will replace provided application source code with the exploded JAR and proceed as described in Building from an Executable Jar.

Example: Building a Native image with Maven

The following command creates an image from source with maven.

pack build samples/java-native \
  --env BP_NATIVE_IMAGE=true
  --path java/native-image/java-native-image-sample
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Building from an Executable JAR

An application developer may build an image from an exploded executable JAR. Most platforms will automatically extract provided archives.

Example: Building a Native image from an Executable JAR

The following command uses Maven directly to compile an executable JAR and then uses the pack CLI to build an image from the JAR.

cd samples/java/native-image
./mvnw package
pack build samples/java-native \
  --env BP_NATIVE_IMAGE=true
  --path java/native-image/java-native-image-sample/target/demo-0.0.1-SNAPSHOT.jar
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The resulting application image will be identical to that built in the “Building a Native image with Maven” example.

About the Native Image

The GraalVM Buildpack will provide the GraalVM JDK, including the native-image utility (the Native image builder), and the Substrate VM.

The Native Image Buildpack uses native-image to compile the Java bytecode into a standalone executable. The Native Image Buildpack uses the standard tools for building native images and does not depend on Spring Native support.

Note: The native-image build is a memory intensive process and may be slow if insufficient memory is provided. From the prerequisites in the Spring Native reference docs:

“On Mac and Windows, it is recommended to increase the memory allocated to Docker to at least 8G (and potentially to add more CPUs as well) since native-image compiler is a heavy process. See this Stackoverflow answer for more details. On Linux, Docker uses by default the resources available on the host so no configuration is needed.”

Inspecting the JVM Version

The exact substrate VM version that was contributed to a given image can be read from the Bill-of-Materials.

Example Inspecting the JRE Version

Given an image named samples/java-native built from one of examples above, the following command will print the exact version of the installed substrate VM.

pack inspect-image samples/java-native --bom | jq '.local[] | select(.name=="native-image-svm") | .metadata.version'
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Configuring the JVM Version

The following environment variable configures the JVM version at build-time.

• BP_JVM_VERSION
  • Defaults to the latest LTS version at the time of release.
  • Configures a specific JVM version.
  • Example: Given BP_JVM_VERSION=8 or BP_JVM_VERSION=8.* the buildpack will install the latest patch releases of the Java 8 JDK and JRE.

Configuring the GraalVM Version

Because GraalVM is evolving rapidly you may on occasion need to, for compatibility reasons, select a sepecific version of the GraalVM and associated tools to use when building an image. This is not a directly configurable option like the JVM version, however, you can pick a specific version by changing the version of the Java Native Image Buildpack you use.

The following table documents the versions available.

GraalVM Version	Java Native Image Buildpack Version
21.1	5.4.0
21.0	5.3.0

For example, to select GraalVM 21.0:

pack build samples/native -e BP_NATIVE_IMAGE=true --buildpack gcr.io/paketo-buildpacks/ca-certificates --buildpack gcr.io/paketo-buildpacks/java-native-image:5.3.0
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Spring Boot Applications

The Java Native Image Buildpack contains the Spring Boot Buildpack and provides the same Spring Boot features as the Java Buildpack.

Selecting a Process

The Java Native Image Buildpack will contribute a default process type that starts the application.

Example: Running the Default Process

Execute the following commands to start the default process type using a samples/java-native image built from any previous example command.

docker run  --rm --publish 8080:8080 samples/java-native
curl -s http://localhost:8080/actuator/health
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Providing Additional Arguments

Additional arguments can be provided to the application using the container [CMD][oci config]. In Kubernetes set CMD using the args field on the [container][kubernetes container resource] resource.

Example: Setting the Server Port

Execute the following command passes an additional argument to application start command, setting the port to 8081.

docker run --rm --publish 8081:8081 samples/java-native --server.port=8081
curl -s http://localhost:8081/actuator/health
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Components

The following component buildpacks compose the Paketo Java Native Image Buildpack.

Buildpack	Required/Optional	Responsibility
Paketo GraalVM Buildpack	Required	Provides the GraalVM JDK and Native Image Substrate VM.
Paketo Gradle Buildpack	Optional	Builds Gradle-based applications from source.
Paketo Leiningen Buildpack	Optional	Builds Leiningen-based applications from source.
Paketo Maven Buildpack	Optional	Builds Maven-based applications from source.
Paketo SBT Buildpack	Optional	Builds SBT-based applications from source.
Paketo Executable JAR Buildpack	Optional	Contributes a process Type that launches an executable JAR.
Paketo Spring Boot Buildpack	Optional	Contributes configuration and metadata to Spring Boot applications.
Paketo Native Image Buildpack	Required	Creates a native image from a JVM application.
Paketo Procfile Buildpack	Optional	Allows the application to define or redefine process types with a Procfile
Paketo Environment Variables Buildpack	Optional	Contributes arbitrary user-provided environment variables to the image.
Paketo Image Labels Buildpack	Optional	Contributes OCI-specific and arbitrary user-provided labels to the image.

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