native-image-configure-examples

Application Initialization at Build Time

This example demonstrates the ability of native-image to run parts of your application at the build time.

In both examples we use the Jackson framework to parse a JSON file to determine which Handler should be used by the application (CurrentTimeHandler or HelloWorldHandler) at runtime.

• In configure-at-runtime-example the JSON parsing happens at image run time and thus contributes to the image startup time. In addition, all methods and static fields originated from the Jackson framework that are needed become part of a native executable.

• In contrast, configure-at-buildtime-example performs the JSON parsing as part of building the native executable. In this case the executable does not contain any parts of the Jackson framework (can be verified easily by adding -H:+PrintAnalysisCallTree to the <buildArgs> in pom.xml). When this image gets executed, it can run right away since it was already determined at build time which handler should be used.

Preparation

1. Download and install the latest GraalVM JDK using SDKMAN!.

   sdk install java 21.0.1-graal

2. Download or clone the repository and navigate into the native-image-configure-examples directory:

   git clone https://github.com/graalvm/graalvm-demos

   cd graalvm-demos/native-image-configure-examples

Build and Run Examples

1. Change to one of the demo subdirectories, for example, configure-at-runtime-example:

   cd graalvm-demos/native-image-configure-examples/configure-at-runtime-example

2. Build the project:

   mvn package

3. Once the Maven build succeeds, a native executable called "runtime-example" will be generated in the configure-at-runtime-example/target/ directory. Run it:

   ./target/runtime-example

   You will see the current date and time message.
4. Repeat the same steps for the other sub-demo:

   cd ../configure-at-buildtime-example

   mvn package

   ./target/buildtime-example

   You will see the next output:

   Hello, world!
   

Loading application configuration at executable build time can speed up application startup.

Related Documentation

• Build-Time Initialization
• Initialize Once, Start Fast: Application Initialization at Build Time