CODESAMPLE

Chain of Responsibility - Dart

Chain of Responsibility Dart

The Chain of Responsibility pattern allows you to pass a request along a chain of handlers. Each handler decides either to process the request or to pass it to the next handler in the chain. This decouples the sender of a request from its receivers, providing flexibility in handling different types of requests.

This Dart implementation defines an abstract RequestHandler class with a nextHandler property. Concrete handlers like AuthenticationRequestHandler, AuthorizationRequestHandler, and LoggingRequestHandler implement the handleRequest method, potentially processing the request and then calling nextHandler.handleRequest(request) if they can’t fully handle it. The client initiates the chain with the first handler. It leverages Dart’s type system and optional chaining to maintain a clean, readable, and flexible design – fitting the generally object-oriented style of Dart.

abstract class RequestHandler {
  RequestHandler? nextHandler;

  void setNext(RequestHandler next) {
    nextHandler = next;
  }

  void handleRequest(String request);
}

class AuthenticationRequestHandler extends RequestHandler {
  @override
  void handleRequest(String request) {
    if (request.startsWith("auth:")) {
      print("Authenticating request: ${request.substring(5)}");
    } else {
      nextHandler?.handleRequest(request);
    }
  }
}

class AuthorizationRequestHandler extends RequestHandler {
  @override
  void handleRequest(String request) {
    if (request.startsWith("authz:")) {
      print("Authorizing request: ${request.substring(6)}");
    } else {
      nextHandler?.handleRequest(request);
    }
  }
}

class LoggingRequestHandler extends RequestHandler {
  @override
  void handleRequest(String request) {
    print("Logging request: $request");
    nextHandler?.handleRequest(request); // Always passes to the next handler
  }
}

void main() {
  // Create the chain
  AuthenticationRequestHandler authHandler = AuthenticationRequestHandler();
  AuthorizationRequestHandler authzHandler = AuthorizationRequestHandler();
  LoggingRequestHandler loggerHandler = LoggingRequestHandler();

  authHandler.setNext(authzHandler);
  authzHandler.setNext(loggerHandler);

  // Send requests
  authHandler.handleRequest("auth:user123");
  authHandler.handleRequest("authz:resource456");
  authHandler.handleRequest("general:some data");
}