This repository contains the code for a demo application for GraalVM.
Download or clone the repository and navigate into the java-kotlin-aot directory:
git clone https://github.com/shelajev/graalvm-demos
cd graalvm-demos/java-kotlin-aot
This is a simple Java / Kotlin application, where a Java method accesses a String from Kotlin and calls a Kotlin function, which later accesses a String from a Java class. This example demonstrates how easy it is to interop between Java and Kotlin.
Before running this example, you need to build the application.
Note that you can use any JDK for building the app, but in the build script we refer to javac in the GraalVM to simplify the prerequisites and not depend on you having another JDK installed.
So export the GraalVM home directory as the $GRAALVM_HOME and add $GRAALVM_HOME/bin to the path. Here's what I have in my ~/.bashrc on my MacBook, note that your paths are likely to be different depending on the download location.
GRAALVM_VERSION=1.0.0-rc11
export GRAALVM_HOME=/Users/${current_user}/repo/graal-releases/graalvm-$GRAALVM_VERSION/Contents/Home
Then execute:
./build.sh
Let's look at the important line of the build.sh which creates a native image from our Java application. The 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 the -H:Class=... and the name of the resulting executable with -H:Name=....
After executing the native-image command, check the directory, it should have produced an executable file helloworld.
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 it both ways and times them with the time utility.
time java -cp ./target/mixed-code-hello-world-1.0-SNAPSHOT-jar-with-dependencies.jar hello.JavaHello
time ./helloworld
On my machine run.sh produces approximately the following output:
→ ./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 0m0.176s
user 0m0.119s
sys 0m0.039s
+ ./helloworld
Hello from Kotlin!
Hello from Java!
real 0m0.008s
user 0m0.003s
sys 0m0.003s
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.
The code from that repository is distributed under the Apache License 2.0. The code in this directory is also distributed under the Apache License 2.0, see LICENSE.md for more details.