How do I set environment variables from Java?

How do I set environment variables from Java? I see that I can do this for subprocesses using ProcessBuilder. I have several subprocesses to start, though, so I’d rather modify the current process’s environment and let the subprocesses inherit it.

There’s a System.getenv(String) for getting a single environment variable. I can also get a Map of the complete set of environment variables with System.getenv(). But, calling put() on that Map throws an UnsupportedOperationException — apparently they mean for the environment to be read only. And, there’s no System.setenv().

So, is there any way to set environment variables in the currently running process? If so, how? If not, what’s the rationale? (Is it because this is Java and therefore I shouldn’t be doing evil nonportable obsolete things like touching my environment?) And if not, any good suggestions for managing the environment variable changes that I’m going to need to be feeding to several subprocesses?

Answer

(Is it because this is Java and therefore I shouldn’t be doing evil nonportable obsolete things like touching my environment?)

I think you’ve hit the nail on the head.

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.