The class NTSystem will help to retrieve the logged in user name and other credentials.
Example:
NTSystem obj = new NTSystem();
System.out.println("Logged In User Name "+obj.getName());
From the java docs :-
This class implementation retrieves and makes available NT security information for the current user.
http://docs.oracle.com/javase/6/docs/jre/api/security/jaas/spec/index.html?com/sun/security/auth/module/package-summary.html
