Chain of Responsibility Pattern - Handling requests through a chain of objects

The Chain of Responsibility pattern is a behavioral design pattern that allows an object to pass a request along a chain of potential handlers until the request is handled or reached the end of the chain. It decouples the sender and receiver of a request, giving multiple objects the opportunity to handle the request.

How it works

In this pattern, each handler has a reference to the next handler in the chain. When a request is made, it is passed to the first object in the chain. If the object can handle the request, it does so; otherwise, it passes the request to the next handler in the chain. This process continues until the request is either handled or there are no more handlers in the chain.

The key components of the Chain of Responsibility pattern are:

1. Handler Interface: Defines the common interface for all handlers in the chain. It declares a method for handling requests and another method for setting the next handler in the chain.
2. Concrete Handlers: Implements the Handler interface and handles requests. Each concrete handler decides whether to handle the request or pass it to the next handler in the chain.
3. Client: Initiates the request and starts the chain of handlers.

Example

Let's consider a real-life scenario to understand the Chain of Responsibility pattern better. Imagine you work in a customer support department of a company, and you receive various customer inquiries. Depending on the nature of the inquiry, it needs to be handled by a specific department. For instance, technical issues are directed to the technical support team, billing inquiries to the accounting team, and so on.

To implement this scenario using the Chain of Responsibility pattern, we can define a Handler interface that declares a method for handling the inquiry and setting the next handler. Each concrete handler, such as TechnicalSupportHandler, AccountingHandler, etc., would implement this interface and provide their own implementation of the handleRequest method. They would either handle the inquiry or pass it to the next handler in the chain if they are not responsible for that specific type of inquiry.

The client, in this case, would create an initial handler and initiate the request by invoking the handleRequest method. The request would then be processed through the chain of handlers until it is either handled or reaches the end of the chain.

Benefits and Usage

The Chain of Responsibility pattern offers several benefits:

• Flexibility and extensibility: The pattern allows for dynamic reordering, adding, or removing of handlers from the chain without impacting the client code.
• Decoupling: It separates the sender of a request from its receivers, enabling a loose coupling between them.
• Multiple handling options: If multiple handlers are capable of handling a request, the chain can be configured to determine the order of handlers to attempt the request.

The Chain of Responsibility pattern is commonly used in scenarios where objects need to process a request based on certain conditions or criteria, especially when the exact handler is not known beforehand. It is often used in logging, exception handling, event processing, and request processing systems.

Conclusion

The Chain of Responsibility pattern provides an elegant way to handle requests by passing them through a chain of objects until the request is handled or reaches the end of the chain. It offers flexibility, decoupling, and multiple handling options. By employing this pattern, you can improve the maintainability and extensibility of your code, as well as make it easier to introduce new handlers or modify the existing ones in a seamless manner.