Build a Native Image of a Java and Kotlin Application
This example demonstrates how to compile a Java and Kotlin application ahead-of-time into a native executable, and illustrates the advantages.
This example requires the Maven build tool.
1. 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 and Kotlin application showing how easy it is to interoperate 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: You can use any JDK for building the application. However,
javac from GraalVM
in the build script is used to simplify the prerequisites so another JDK does not need to be installed.
2. Having installed GraalVM, export the home directory as
$GRAALVM_HOME and add
to the path, using a command-line shell for Linux:
For macOS, use:
Note that your paths are likely to be different depending on the download location.
3. Install Native Image to make use of the
4. Then execute:
Have a look at the
build.sh script which creates a native executable from a Java class.
native-image utility compiles 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 few 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 the executable file,
Running the Application
To run the application, you need to execute the JAR file in the
You can run it as a normal Java application using
Or, since we have a native executable 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
An output close to the following 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.
This sample application is taken from the JetBrains Kotlin-examples repository. It is distributed under the Apache License 2.0.