GraalVM demos: AOT compilation of a Java / Kotlin application
This is an example of a GraalVM demo application that shows ahead-of-time compilation of Java and Kotlin code.
Download or clone the repository and navigate into the
git clone https://github.com/graalvm/graalvm-demos cd graalvm-demos/java-kotlin-aot
This is a simple Java / Kotlin application showing how easy it is to interop between JVM-based languages. A Java method accesses a String from Kotlin and calls a Kotlin function, which later accesses a String from a Java class. Before running this example, you need to build the application.
Note that you can use any JDK for building the application, however we refer
javac from GraalVM in the build script to simplify the prerequisites
and not to depend on another JDK installed.
Export the GraalVM home directory as the
$GRAALVM_HOME and add
to the path, using a command-line shell for Linux:
and for Mac OS:
Note that your paths are likely to be different depending on the download location.
Have a look at the
build.sh script which creates a native image from the Java class.
native-image utility is a part of GraalVM. It is used to compile
applications ahead-of-time for faster starup 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 have
produced an executable file
Running the application
To run the application, you need to execute the fat jar file in the
You can run it as a normal Java application using
Or, since we have a native image prepared, you can run that directly.
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 ./helloworld
Approximately, the following output should be produced:
→ ./run.sh + java -cp ./target/mixed-code-hello-world-1.0-SNAPSHOT-jar-with-dependencies.jar hello.JavaHello Hello from Kotlin! Hello from Java! real 0m0.129s user 0m0.094s sys 0m0.034s + ./helloworld Hello from Kotlin! Hello from Java! real 0m0.010s user 0m0.003s sys 0m0.004s
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.