How to set environment variable from java code and use this variable without restarting my workspace

Question

I have a requirement where I need to run a command which needs an environment variable value to be present beforehand on Windows OS. I tried using

Process p = Runtime.getRuntime().exec("cmd.exe","/c","setx","ENVVAR","somevalue");
p=Runtime.getRuntime().exec("cmd.exe","/c","COMMANDTHATUSEENVAR");

Though this ENVVAR is set but the next command when runs give the error the ENVAR is not set. Now when I restart my workspace and run above code it happily takes the ENVAR value. But the problem is I cannot restart my workspace every time. So is there any possible solution where I get to set the environment variable and also use that value without restarting my workspace.

Answer 1

You could try the /V option, and try to built a single command, like the following example :

cmd /V /C "set EDITOR=vim&& echo !EDITOR!"

So my suggestion: first build a string that does what you need on the command line. Then translate that into something that works with the Java ProcessBuilder.

Alternatively: you could create a simple batch script that takes the ENVAR value as argument ; sets the ENVAR and then runs your tool.

In the end, your problem is that the ProcessBuilder will fork a new Process; so the "changes" that you make there are not visible when forking of another process later on. When you re-start your eclipse, that runs in a completely new process which sees those updates made by your first system call.

Answer 2

By default the environemnt block is copied from parent process to child process, but you can change the environment copy of the process you start.

public class EnvironmentTest
{
    public static void main(String[] args) throws Exception
    {
        ProcessBuilder pb = new ProcessBuilder(
            "CMD.exe"
            , "/C"
            , "start \"\" cmd /c \"set e & pause\""
        );
        pb.environment().put("ENVVAR", "This is a test");
        Process p = pb.start();
    }
}

The cmd instance started inside the ProcessBuilder has the environment variable defined. To show it, this instance is starting another one (the start "" cmd ... ) to show in screen the value in the variable.

Probably in your case you will need something like

public class EnvironmentTest
{
    public static void main(String[] args) throws Exception
    {
        ProcessBuilder pb = new ProcessBuilder(
            "CMD.exe"
            , "/C"
            , "start \"\" \"COMMANDTHATUSEEN‌​VAR\""
        );
        pb.environment().put("ENVVAR", "This is a test");
        Process p = pb.start();
    }
}