Example used at http://craftedsw.blogspot.com/2011/07/testing-legacy-hard-wired-dependencies.html

TripService.java

public class TripService {

	public List<Trip> getTripsByUser(User user) throws UserNotLoggedInException {
		List<Trip> tripList = new ArrayList<Trip>();
		User loggedUser = loggedUser();
		boolean isFriend = false;
		if (loggedUser != null) {
			for (User friend : user.getFriends()) {
				if (friend.equals(loggedUser)) {
					isFriend = true;
					break;
				}
			}
			if (isFriend) {
				tripList = findTripsByUser(user);
			}
			return tripList;
		} else {
			throw new UserNotLoggedInException();
		}
	}
	
	protected List<Trip> findTripsByUser(User user) {
	    return TripDAO.findTripsByUser(user);
	}
	  
	protected User loggedUser() {
	    return UserSession.getInstance().getLoggedUser();
	}
	
}