Get login username in java

How can I get the username/login name in Java?

This is the code I have tried...

try{
    LoginContext lc = new LoginContext(appName,new TextCallbackHandler());
    lc.login();
    Subject subject = lc.getSubject();
    Principal principals[] = (Principal[])subject.getPrincipals().toArray(new Principal[0]);

    for (int i=0; i<principals.length; i++) {
        if (principals[i] instanceof NTUserPrincipal || principals[i] instanceof UnixPrincipal) {
            String loggedInUserName = principals[i].getName();
        }
    }

}
catch(SecurityException se){
    System.out.println("SecurityException: " + se.getMessage());
}

I get a SecurityException when I try to run this code. Could someone please tell me whether I'm heading in the right direction, and help me to understand the problem.

Solution 1:

System.getProperty("user.name");

Solution 2:

in Unix:

new com.sun.security.auth.module.UnixSystem().getUsername()

in Windows:

new com.sun.security.auth.module.NTSystem().getName()

in Solaris:

new com.sun.security.auth.module.SolarisSystem().getUsername()