Is it possible to set an environment variable at runtime from Java?

Question

Is it possible to set an environment variable at runtime from a Java application? In Java 1.5 java.lang.System class there is the getenv() method, I would only need a setenv

Answer 1

You can get a handle on the underlying map that java.lang.ProcessEnvironment is holding on to, and then put new stuff and remove stuff all you want.

This works on java 1.8.0_144. Can't guarantee it works on any other version of java, but it's probably similar if you really need to change the environment at run time.

private static Map getModifiableEnvironment() throws Exception{
    Class pe = Class.forName("java.lang.ProcessEnvironment");
    Method getenv = pe.getDeclaredMethod("getenv");
    getenv.setAccessible(true);
    Object unmodifiableEnvironment = getenv.invoke(null);
    Class map = Class.forName("java.util.Collections$UnmodifiableMap");
    Field m = map.getDeclaredField("m");
    m.setAccessible(true);
    return (Map) m.get(unmodifiableEnvironment);
}

After you get the reference to the map, just add whatever you want and you can now retrieve it using the regular old System.getenv("") call.

I tried this its working in MAC not working in Windows in both os java version 1.8_161