How do I persistently define environment variables in Java on Windows?

Question

Is there a way to change Windows environment variables using Java? I tried with the cmd function set:

Process exec = Runtime.getRuntime().exec(new String[] {
      "cmd", "/c", "set", "HTTP_PROXY=" + PROXY_URL
});

if (exec.waitFor() != 0) {
    throw new IllegalStateException("Output: "
        + getText(exec.getInputStream())
        + "Error: " + getText(exec.getErrorStream()
        + "\n"
        + "Exit value: " + exec.exitValue());
}

This code runs fine without any error but when I later check system variables nothing has changed.

I'm trying to update HTTP_PROXY so that other software run behind an HTTP proxy can use it.

Hi Ramesh could you elaborate a bit on what you are trying to achieve? — jirungaray, May 03 '15 at 15:41
You are not making a persistent change. You update the value inside the process you create only. — PM 77-1, May 03 '15 at 15:46
I want to change HTTP_PROXY env var so that I can run software like php composer behind proxy. Is there any way to do that without changing system variables..? — Ramesh-X, May 03 '15 at 15:55
I liked how this was asked in 2008 and it's responses - http://stackoverflow.com/questions/318239/how-do-i-set-environment-variables-from-java - not a dupe though — kiranpradeep, May 03 '15 at 17:30

Raffaele · Accepted Answer · 2015-05-03T16:11:17.193

Processes are launched in an enviroment made of name-value pairs. When a program writes to an env variable, it can optionally make that write visible to child processes, but when you check the value you are likely using another process (maybe run via cmd.exe) that has no access to the environment of your Java program.

I don't know if the purpose of your code is to define environment variables in a persistent manner, but if that's the case it can't be done in Java without specific OS tools and in a platform-independent way.

Environment variables default values must be stored by system tools in places where they are then read by the very same system tools from. On Linux there are files like .profile and .bashrc in the user home, while on Windows you have the registry. For example on my Windows 7 I have: my PATH default value stored in \HKEY_CURRENT_USER\Environment - so you must find a way to write to the system registry, for example the command reg

The REG ADD command allows the user to add new keys and values to the Registry. To display the full range of parameters that can be used, type the following into the command line: reg add /?

To add the key HKLM\Software\MyNewApp on remote computer PC2, type:
REG ADD \\PC2\HKLM\Software\MyNewApp
To add a registry entry to HKLM\Software\MyNewApp with a value named Data of type REG_BINARY and data of fe340ead, type:
REG ADD HKLM\Software\MyNewApp /v Data /t REG_BINARY /d fe340ead

You can either write a .bat script or call reg from your Java program. You may need administrator priviledges and to restart some programs (eventually the whole machine) for the update to take effect (for example restart explorer.exe)

score 0 · Answer 2 · edited May 03 '15 at 16:13

0

It's impossible to do that (at least for forever). There are good reasons for that (isolation, java tools unknowingly changing your env). Look for a hack here :

edit:

a complex explanation was given by raffaele

edited May 03 '15 at 16:13

Am_I_Helpful

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answered May 03 '15 at 15:44

phiology

29
3

No, that's not the thing I want. I want to change a system variable so that other softwares can use it. (Those softwares do not executed by my java software).. I think my task is impossible then.. – Ramesh-X May 03 '15 at 16:00
thats what i mean. give general permissions by altering your path manually (why not if this is the desired effect). why would you want to set it permanently from java anyways if your ENV is supposed to stay forever? – phiology May 03 '15 at 16:09

How do I persistently define environment variables in Java on Windows?

2 Answers2