chainofresponsibility

Chain of responsibility is a behavioral design pattern that passes a request along a chain of potential handlers until one handles it. The sender remains unaware of which component will process the request, or even if a handler exists, allowing decoupling between the requester and the receiver. This pattern is commonly used to avoid long conditional statements and to enable dynamic, configurable processing pipelines.

Participants typically include a Handler interface with a method to set the next handler and a method to handle the request. ConcreteHandler implementations decide whether to process the request or forward it to the next handler in the chain. A client constructs the chain and initiates the request. The chain can be modified at runtime, enabling flexible composition of handlers.

Behaviorwise, the request enters the chain and is passed from handler to handler. A handler that can process the request does so and may terminate the chain. If none can handle it, the request may be dropped, logged, or routed to a default or fallback handler. The pattern emphasizes loose coupling, extensibility, and the ability to add, remove, or reorder handlers without altering the client code.

Advantages include decoupling of sender and receiver, improved maintainability, and the ability to configure processing steps at runtime. Disadvantages include potential for unhandled requests, performance overhead, and the need for careful chain management to avoid cycles or dead ends.

Common use cases are middleware pipelines in web frameworks, event handling in GUI systems, and error or validation processing chains. Implementations often resemble pipelines where each component decides to handle or delegate the work.