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Access Environment Variables in a Native Executable at Runtime

docs/reference-manual/native-image/guides/access-environment-variables.md

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Access Environment Variables in a Native Executable at Runtime

A native executable accesses environment variables in the same way as a regular Java application.

Run a Demo

For example, run a Java application that iterates over your environment variables and prints out the ones that contain the String of characters passed as a command-line argument.

Prerequisite

Make sure you have installed a GraalVM JDK. The easiest way to get started is with SDKMAN!. For other installation options, visit the Downloads section.

  1. Save the following source code in a file named EnvMap.java:

    java
    import java.util.Map;

public class EnvMap {
    public static void main (String[] args) {
        var filter = args.length > 0 ? args[0] : "";
        Map<String, String> env = System.getenv();
        for (String envName : env.keySet()) {
            if(envName.contains(filter)) {
                System.out.format("%s=%s%n",
                                envName,
                                env.get(envName));
            }
        }
    }
}

  2. Compile the file and build a native executable, as follows:

    shell
    javac EnvMap.java
    shell
    native-image EnvMap

  3. Run the native application and pass a command-line argument, such as "HELLO". There should be no output, because there is no environment variable with a matching name.

    shell
    ./envmap HELLO
<no output>

  4. Create a new environment variable named "HELLOWORLD" and give it the value "Hello World!". (If you are using a bash shell, follow the example below.) Now, run the native executable again—it will correctly print out the name and value of the matching environment variable(s).

    shell
    export HELLOWORLD='Hello World!'
    shell
    ./envmap HELLO

    You should receive the expected output:

    HELLOWORLD=Hello World!