How to modify environment variable in JAVA.

We can get the environment variable using java System.getenv("env-name").

But there is no setter for this.

You can set it like this

import java.lang.reflect.Field;

import java.util.Collections;

import java.util.HashMap;

import java.util.Map;

public class Test {

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

Map map = System.getenv();

Map newmap = new HashMap();

newmap.putAll(map);

newmap.put("abc", "----------");

setEnv(newmap);

System.out.println(map);

System.out.println("done");

System.out.println(System.getenv("abc"));

newmap.remove("abc");

setEnv(newmap);

System.out.println(System.getenv("abc"));

}

private static void setEnv(Map newenv)

{

 try

   {

       Class processEnvironmentClass = Class.forName("java.lang.ProcessEnvironment");

       Field theEnvironmentField = processEnvironmentClass.getDeclaredField("theEnvironment");

       theEnvironmentField.setAccessible(true);

       Map env = (Map) theEnvironmentField.get(null);

       env.putAll(newenv);

       Field theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment");

       theCaseInsensitiveEnvironmentField.setAccessible(true);

       Map cienv = (Map)     theCaseInsensitiveEnvironmentField.get(null);

       cienv.putAll(newenv);

   }

   catch (NoSuchFieldException e)

   {

     try {

       Class[] classes = Collections.class.getDeclaredClasses();

       Map env = System.getenv();

       for(Class cl : classes) {

           if("java.util.Collections$UnmodifiableMap".equals(cl.getName())) {

               Field field = cl.getDeclaredField("m");

               field.setAccessible(true);

               Object obj = field.get(env);

               Map map = (Map) obj;

               map.clear();

               map.putAll(newenv);

           }

       }

     } catch (Exception e2) {

       System.out.println(e2);

     }

   } catch (Exception e1) {

    System.out.println(e1);

   } 

}

}