Łańcuch zobowiązań w języku Java

package refactoring_guru.chain_of_responsibility.example.middleware; /** * Base middleware class. */ public abstract class Middleware { private Middleware next; /** * Builds chains of middleware objects. */ public static Middleware link(Middleware first, Middleware... chain) { Middleware head = first; for (Middleware nextInChain: chain) { head.next = nextInChain; head = nextInChain; } return first; } /** * Subclasses will implement this method with concrete checks. */ public abstract boolean check(String email, String password); /** * Runs check on the next object in chain or ends traversing if we're in * last object in chain. */ protected boolean checkNext(String email, String password) { if (next == null) { return true; } return next.check(email, password); } } 

package refactoring_guru.chain_of_responsibility.example.middleware; /** * ConcreteHandler. Checks whether there are too many failed login requests. */ public class ThrottlingMiddleware extends Middleware { private int requestPerMinute; private int request; private long currentTime; public ThrottlingMiddleware(int requestPerMinute) { this.requestPerMinute = requestPerMinute; this.currentTime = System.currentTimeMillis(); } /** * Please, not that checkNext() call can be inserted both in the beginning * of this method and in the end. * * This gives much more flexibility than a simple loop over all middleware * objects. For instance, an element of a chain can change the order of * checks by running its check after all other checks. */ public boolean check(String email, String password) { if (System.currentTimeMillis() > currentTime + 60_000) { request = 0; currentTime = System.currentTimeMillis(); } request++; if (request > requestPerMinute) { System.out.println("Request limit exceeded!"); Thread.currentThread().stop(); } return checkNext(email, password); } } 

package refactoring_guru.chain_of_responsibility.example.middleware; import refactoring_guru.chain_of_responsibility.example.server.Server; /** * ConcreteHandler. Checks whether a user with the given credentials exists. */ public class UserExistsMiddleware extends Middleware { private Server server; public UserExistsMiddleware(Server server) { this.server = server; } public boolean check(String email, String password) { if (!server.hasEmail(email)) { System.out.println("This email is not registered!"); return false; } if (!server.isValidPassword(email, password)) { System.out.println("Wrong password!"); return false; } return checkNext(email, password); } } 

package refactoring_guru.chain_of_responsibility.example.middleware; /** * ConcreteHandler. Checks a user's role. */ public class RoleCheckMiddleware extends Middleware { public boolean check(String email, String password) { if (email.equals("admin@example.com")) { System.out.println("Hello, admin!"); return true; } System.out.println("Hello, user!"); return checkNext(email, password); } } 

package refactoring_guru.chain_of_responsibility.example.server; import refactoring_guru.chain_of_responsibility.example.middleware.Middleware; import java.util.HashMap; import java.util.Map; /** * Server class. */ public class Server { private Map<String, String> users = new HashMap<>(); private Middleware middleware; /** * Client passes a chain of object to server. This improves flexibility and * makes testing the server class easier. */ public void setMiddleware(Middleware middleware) { this.middleware = middleware; } /** * Server gets email and password from client and sends the authorization * request to the chain. */ public boolean logIn(String email, String password) { if (middleware.check(email, password)) { System.out.println("Authorization have been successful!"); // Do something useful here for authorized users. return true; } return false; } public void register(String email, String password) { users.put(email, password); } public boolean hasEmail(String email) { return users.containsKey(email); } public boolean isValidPassword(String email, String password) { return users.get(email).equals(password); } } 

package refactoring_guru.chain_of_responsibility.example; import refactoring_guru.chain_of_responsibility.example.middleware.Middleware; import refactoring_guru.chain_of_responsibility.example.middleware.RoleCheckMiddleware; import refactoring_guru.chain_of_responsibility.example.middleware.ThrottlingMiddleware; import refactoring_guru.chain_of_responsibility.example.middleware.UserExistsMiddleware; import refactoring_guru.chain_of_responsibility.example.server.Server; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /** * Demo class. Everything comes together here. */ public class Demo { private static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); private static Server server; private static void init() { server = new Server(); server.register("admin@example.com", "admin_pass"); server.register("user@example.com", "user_pass"); // All checks are linked. Client can build various chains using the same // components. Middleware middleware = Middleware.link( new ThrottlingMiddleware(2), new UserExistsMiddleware(server), new RoleCheckMiddleware() ); // Server gets a chain from client code. server.setMiddleware(middleware); } public static void main(String[] args) throws IOException { init(); boolean success; do { System.out.print("Enter email: "); String email = reader.readLine(); System.out.print("Input password: "); String password = reader.readLine(); success = server.logIn(email, password); } while (!success); } } 

Enter email: admin@example.com Input password: admin_pass Hello, admin! Authorization have been successful! Enter email: wrong@example.com Input password: wrong_pass This email is not registered! Enter email: wrong@example.com Input password: wrong_pass This email is not registered! Enter email: wrong@example.com Input password: wrong_pass Request limit exceeded!