Chain of Responsibility - GoF Way

Authenticator.java

abstract class Authenticator {
	private Authenticator next;
	
	public static Authenticator chain() {
		Authenticator defaultMethod = new EmailAuthenticator();
		Authenticator networkMethod = new NetworkAuthenticator();
		defaultMethod.setNext(networkMethod);
		
		Authenticator partnerMethod = new PartnerAuthenticator();
		networkMethod.setNext(partnerMethod);
		
		return defaultMethod;
	}
	
	public void setNext(Authenticator auth) { this.next = auth; }
	
	public boolean login(String username, String password) {
		if (canAuthenticate(username, password)) {
			return authenticate(username, password);
		}
		
		if (next == null) {
			return false;
		}
		
		return next.login(username, password);
	}
	
	abstract boolean canAuthenticate(String username, String password);
	abstract boolean authenticate(String username, String password);
}

EmailAuthenticator.java

class EmailAuthenticator extends Authenticator {
	
	public boolean canAuthenticate(String username, String password) {
		return username.indexOf("@") > 0;
	}
	
	public boolean authenticate(String username, String password) {
		// do email authentication
		return true;
	}
}

HellYeahController.java

public class HellYeahController {
	public void loginAction(Request request, Response response) {
		boolean userLoggedIn = UserAuthenticator.login(
									request.getParameter("username@foo.com"), 
									request.getParameter("password1")
								);
		if (userLoggedIn) {
			System.out.println("WOW!");
		} else {
			System.out.println("OH NO!");
		}
	}
}

NetworkAuthenticator.java

class NetworkAuthenticator extends Authenticator {
	public boolean canAuthenticate(String username, String password) {
		return username.indexOf("/") > 0;
	}
	
	public boolean authenticate(String username, String password) {
		// do network authentication
		return true;
	}
}

PartnerAuthenticator.java

class PartnerAuthenticator extends Authenticator {
	public boolean canAuthenticate(String username, String password) {
		return username.startsWith("/") && username.length() > 12 && username.endsWith("@");
	}
	
	public boolean authenticate(String username, String password) {
		// do far away partner authentication
		return true;
	}
}

Request.java

class Request {
	public String getParameter(String key) { return key; }
}

Response.java

class Response {}

UserAuthenticator.java

class UserAuthenticator {
	
	public static boolean login(String username, String password) {
		return Authenticator.chain().login(username, password);
	}
}

There is more LOC than POG version, but this one is more testable; extensible; readable and will keep you employed. :)