Applied Design Patterns with Java

Behavioral :: Chain of Responsibility (223) {C ch 16}

Applicability

Use the Chain of Responsibility pattern when:

• more than one object may handle a request, and the handler isn't known in advance. The handler should be determined automatically;
• there is a need to issue a request to one of several objects without specifying the receiver explicitly;
• the set of objects that can handle a request should be specified dynamically.

Structure

A typical object structure might look like this:

Participants

• Handler (HelpHandler) defines an interface for handling requests, and optionally implements the successor link.
• ConcreteHandler (PrintButton, PrintDialog) handles requests it is responsible for, can access its successor, and if the ConcreteHandler can handle the request, it does so; otherwise it forwards the request to its successor.
• Client initiates the request to a ConcreteHandler object on the chain.

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