How to add an environment variable in Java?

Question

Possible Duplicate:
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 ?

```java java.lang.UnsupportedOperationException at java.util.Collections$UnmodifiableMap.put(Collections.java:1457) at br.com.stilingue.services.remove_occupation.RemoveOccupationTest.setUpTestEnv(RemoveOccupationTest.java:29) ``` — Michael Pacheco, Apr 01 '19 at 14:45

stacker · Accepted Answer · 2013-01-18T13:02:55.523

9

 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.

edited Jan 18 '13 at 13:02

answered Jan 18 '13 at 12:43

stacker

66,311
27
138
208

thanks, but env.put("MV_ENV_VAR", "1"); will set the env variable only in local variable, but if u again take processbuilder instance and get the content of map, it will not show the variable that we have set as mentioned by you. – BSalunke Jan 18 '13 at 12:46
@BSalunke updated my answer and added an example. – stacker Jan 18 '13 at 13:04

score 5 · Answer 2 · answered Jan 18 '13 at 12:45

5

You can add the desired variables directly into ProcessBuilder.environment() map. The code below should work:

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

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

    ProcessBuilder pb = new ProcessBuilder("/bin/sh"); // or any other program you want to run

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

    envMap.put("MY_ENV_VAR", "1");
    Set<String> keys = envMap.keySet();
    for(String key:keys){
        System.out.println(key+" ==> "+envMap.get(key));
    }

}

}

answered Jan 18 '13 at 12:45

maksim_khokhlov

794
5
8

@masksim_khokhlov what if we again took the processBuilder instance and get the contained of map? it will not contain our variable – BSalunke Jan 18 '13 at 12:52
1

@BSalunke Why it won't? It will! ProcessBuilder.environment() will always return the same `Map` instance. Check out the [javadoc](http://docs.oracle.com/javase/6/docs/api/java/lang/ProcessBuilder.html). – maksim_khokhlov Jan 18 '13 at 13:14

score 3 · Answer 3 · answered Jan 18 '13 at 12:45

3

You can get the environment variable with the process Builder object :

    ProcessBuilder pb = new ProcessBuilder("myCommand", "myArg1", "myArg2");
    Map<String, String> env = pb.environment();
    env.put("VAR1", "myValue");
    env.remove("OTHERVAR");
    env.put("VAR2", env.get("VAR1") + "suffix");

answered Jan 18 '13 at 12:45

Dimitri

7,858
18
72
124

It looks like `pb.start()` is missing. – Zon Jan 04 '22 at 08:00

score 1 · Answer 4 · edited May 23 '17 at 10:30

From how-do-i-set-environment-variables-from-java

A possible way to ease the burden would be to factor out a method

void setUpEnvironment(ProcessBuilder builder) {
    Map<String, String> env = builder.environment();
    // blah blah
}

and pass any ProcessBuilders through it before starting them.

Also, you probably already know this, but you can start more than one process with the same ProcessBuilder. So if your subprocesses are the same, you don't need to do this setup over and over.

How to add an environment variable in Java?

4 Answers4

Linked