System.getenv() - Behavior depends on whether debug mode is enabled

Question

I try to retrieve the windows directory of my OS. To get the correct path I tried the following 2 commands:

System.getenv().get("WINDIR")
System.getenv().get("SystemRoot")

Both commands work, but the strange thing is, that the first command (WINDIR) returns the path only, if I run the program in debug mode. The latter command (SystemRoot) returns the path only if I run the program not in debug mode.

So this program

public static void main(String[] args) {
    System.out.println(System.getenv().get("WINDIR"));
    System.out.println(System.getenv().get("SystemRoot"));
}

evaluates to

// Debug mode
C:\Windows
null

// No Debug mode
null
C:\Windows

Is this a defined behavior?

(My application is Windows specific, and if i speak of debug mode I mean the default Eclipse "Debug as Java Applicaton" run configiguration)

Answer 1

System.getEnv() is an overloaded method, one implementation having no parameters and one having a String parameter.

• static Map getenv​() Returns an unmodifiable string map view of the current system environment.
• static String getenv​(String name) Gets the value of the specified environment variable.

You are calling the implementatation with no parameters, and then calling get() on the returned Map. From the Javadoc for System.getEnv():

• For getEnv(): The returned map is typically case-sensitive on all platforms.
• For getEnv(String): On UNIX systems the alphabetic case of name is typically significant, while on Microsoft Windows systems it is typically not.

So it is essential for your code to be providing the name of the environment variable in the correct case, specifying windir in all lower case, not upper case.

That said, I can't explain the differences you see when running in debug mode at all. If I run the program below - which is just an enhanced version of yours - I get identical results (as expected) regardless of whether it is run in debug mode or not:

System.getenv().get() windir=C:\WINDOWS
System.getenv().get() WINDIR=null
System.getenv().get() systemroot=null
System.getenv().get() SystemRoot=C:\WINDOWS
System.getenv()       windir=C:\WINDOWS
System.getenv()       WINDIR=C:\WINDOWS
System.getenv()       systemroot=C:\WINDOWS
System.getenv()       SystemRoot=C:\WINDOWS

Could you run the code below twice, once in debug mode and once in normal mode, and advise of the results? Also, advise of your environment: Windows version, Eclipse version and Java version.

[This is more of a request for further information than a final answer, but I couldn't fit it all into a comment.]

import java.lang.management.ManagementFactory;
import java.util.regex.Pattern;

public class App {

    private final static Pattern debugPattern = Pattern.compile("-Xdebug|jdwp");

    public static boolean isDebugging() {
        // https://stackoverflow.com/questions/7397584/how-to-know-my-code-is-running-in-debug-mode-in-ide
        // Taken from the code provided by SO user AlexR
        for (String arg : ManagementFactory.getRuntimeMXBean().getInputArguments()) {
            if (debugPattern.matcher(arg).find()) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {

        System.out.println("Running in debug mode? " + App.isDebugging());
        System.out.println("System.getenv().get() windir=" + System.getenv().get("windir"));
        System.out.println("System.getenv().get() WINDIR=" + System.getenv().get("WINDIR"));
        System.out.println("System.getenv().get() systemroot=" + System.getenv().get("systemroot"));
        System.out.println("System.getenv().get() SystemRoot=" + System.getenv().get("SystemRoot"));
        System.out.println("System.getenv()       windir=" + System.getenv("windir"));
        System.out.println("System.getenv()       WINDIR=" + System.getenv("WINDIR"));
        System.out.println("System.getenv()       systemroot=" + System.getenv("systemroot"));
        System.out.println("System.getenv()       SystemRoot=" + System.getenv("SystemRoot"));
    }

}