Question

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How do I set environment variables from Java?

I’m working on Java. I have to add an environment variable in java code programmatic such that it will be available when i get list using process builder as follows:

import java.util.Map;
import java.util.Set;

class helloworld  {
    public static void main(String[] args) {

        ProcessBuilder pb = new ProcessBuilder("export MY_ENV_VAR=1");

        Map<String, String> envMap = pb.environment();

        Set<String> keys = envMap.keySet();
        for(String key:keys){
            System.out.println(key+" ==> "+envMap.get(key));
        }

    }
}

But with above trial i cant get environment variable properly.
so How to set the environment variable ?

Answer 1

 Map<String, String> env = pb.environment();
 env.put("MV_ENV_VAR", "1");

would set MY_ENV_VAR=1. Before you invoke the Process by

Process p = pb.start();

export would only be interpreted by a shell.

See also ProcessBuilder

A full example:

public static void main(String[] args) throws IOException {

    ProcessBuilder pb = new ProcessBuilder("CMD", "/C", "SET");
    Map<String, String> env = pb.environment();
    env.put("MYVAR", "myValue");
    Process p = pb.start();
    InputStreamReader isr = new InputStreamReader(p.getInputStream());
    char[] buf = new char[1024];
    while (!isr.ready()) {
        ;
    }
    while (isr.read(buf) != -1) {
        System.out.println(buf);
    }
}

prints among other environment values:

MYVAR=myValue

This should prove that the created process uses the manipulated environment.