This is an example of a GraalVM demo application that shows ahead-of-timecompilation of Java and Kotlin code.
- Download or clone the repository and navigate into the
git clone https://github.com/graalvm/graalvm-demos
This is a simple Java / Kotlin application showing how easy it is to interopbetween JVM-based languages. A Java method accesses a String from Kotlin andcalls a Kotlin function, which later accesses a String from a Java class. Beforerunning this example, you need to build the application. Note that you can useany JDK for building the application, however we refer to
javac from GraalVMin the build script to simplify the prerequisites and not to depend on anotherJDK installed.
- Having downloaded and unzipped GraalVM CE or EE archive, export the GraalVM home directory as the
$GRAALVM_HOME/binto the path, using a command-line shell for Linux:
and for macOS:
Note that your paths are likely to be different depending on the download location.
Make sure the
native-imageutility is available. Starting from GraalVM 19.0, Native Image was extracted from the base distribution. This functionality can be added to the core installation with GraalVM Updater tool by running:
gu install native-image.
Have a look at the
build.sh script which creates a native image from the Java class.The
native-image utility compile the application ahead-of-time for faster startup and lower general overhead at runtime.
$GRAALVM_HOME/bin/native-image -cp ./target/mixed-code-hello-world-1.0-SNAPSHOT.jar -H:Name=helloworld -H:Class=hello.JavaHello-H:+ReportUnsupportedElementsAtRuntime--allow-incomplete-classpath
It takes a couple of parameters, the classpath, the main class of the application with
-H:Class=… and the name of the resulting executable with
After executing the
native-image command, check the directory, it should haveproduced an executable file
To run the application, you need to execute the fat jar file in the
target dir.You can run it as a normal Java application using
java.Or, since we have a native image prepared, you can run that directly.The
run.sh file executes both, and times them with the
java -cp ./target/mixed-code-hello-world-1.0-SNAPSHOT-jar-with-dependencies.jar hello.JavaHello
Approximately, the following output should be produced:
+ java -cp ./target/mixed-code-hello-world-1.0-SNAPSHOT-jar-with-dependencies.jar hello.JavaHello
The performance gain of the native version is largely due to the faster startup.
The sample application in this directory is taken from the JetBrains Kotlin-examples repository.It is distributed under the Apache License 2.0.