core/src/main/java/org/springframework/security/authentication/jaas/JaasNameCallbackHandler.java
public void handle(Callback callback, Authentication authentication)
			throws IOException, UnsupportedCallbackException {
		if (callback instanceof NameCallback) {
			NameCallback ncb = (NameCallback) callback;
			String username;

			Object principal = authentication.getPrincipal();

			if (principal instanceof UserDetails) {
				username = ((UserDetails) principal).getUsername();
			}
			else {
				username = principal.toString();
			}

			ncb.setName(username);
		}
	}
public void handle(Callback callback, Authentication authentication)
			throws IOException, UnsupportedCallbackException {
		if (callback instanceof NameCallback) {
			NameCallback ncb = (NameCallback) callback;
			String username;

			Object principal = authentication.getPrincipal();

			if (principal instanceof UserDetails) {
				username = ((UserDetails) principal).getUsername();
			}
			else {
				username = principal.toString();
			}

			ncb.setName(username);
		}
	}
public void handle ( Callback callback , Authentication authentication ) throws IOException , UnsupportedCallbackException { if ( callback instanceof NameCallback ) { NameCallback ncb = ( NameCallback ) callback ; String username ; Object principal = authentication . getPrincipal ( ) ; if ( principal instanceof UserDetails ) { username = ( ( UserDetails ) principal ) . getUsername ( ) ; } else { username = principal . toString ( ) ; } ncb . setName ( username ) ; } }
If the callback passed to the 'handle' method is an instance of NameCallback, the
JaasNameCallbackHandler will call,
callback.setName(authentication.getPrincipal().toString()).

@param callback
@param authentication

@throws IOException
@throws UnsupportedCallbackException
If the callback passed to the handle method is an instance of NameCallback the JaasNameCallbackHandler will call callback . setName ( authentication . getPrincipal () . toString () ) .