PROPERTIES.md

Using System Properties in Substrate VM images

Lets assume you have the following Java Program

public class App {
    public static void main(String[] args) {
        System.getProperties().list(System.out);
    }
}

If you compile that with e.g. native-image -Dfoo=bar App the system property foo will be available at image build-time. I.e. whenever you are in code that is part of your application but executed at image build-time (usually static field initializations & static initializers). Thus if you execute the image above it will not contain foo in the list of properties.

If, on the other hand, you now execute the image with: app -Dfoo=bar it will show foo in the list of properties because you specified it for image run-time.

In other words:

• Passing -D<key>=<value> to native-image affects properties seen at image build-time.
• Passing -D<key>=<value> to an image execution affects properties seen at image run-time.