To read Environment Variables in java

You can retrieve the Java-defined system properties in your code using the
System.getProperty()method.
You can use the following code to determine which are the Java-defined system
properties on your machine:
public static void main( String [] args ) {
java.util.Properties p = System.getProperties();
java.util.Enumeration keys = p.keys();
while( keys.hasMoreElements() ) {
System.out.println( keys.nextElement() );
}
}

If you have read the value of an environment value set on your Windows OS (for
example the value of path variable), then you would have to do the following:

public static void main(String[] args)
{
String path = System.getProperty("path");
System.out.println("the value of path is "+path);
}

While running the above code, you would have to run it as:
java -Dpath="%path%" myClassname

Thus, whatever environment variable that you want to read in your java file, you
would need to specify that in the java command while running the file.
eg:
java -Dpath="%path%" -Dclasspath="%classpath%" myClassname

Do let me know if you have any more questions.

Rgds,
Rashmi