Static Class Structure

• Sender
  • Refers to the Handler interface to handle a request (handler.handleRequest())
    and is independent of how the request is handled (which handler handles the request).
  • Maintains a reference (handler) to a Handler object on the chain.
• Handler
  • Defines an interface for handling a request.
  • Maintains a reference (successor) to the next Handler object on the chain.
• Receiver1,Receiver2,Receiver3,…
  • Implement the Handler interface
    by either handling a request directly or forwarding it to the next handler (if any) on the chain.

Dynamic Object Collaboration

• In this sample scenario, a Sender object sends a request to a Handler object on the chain. The request gets forwarded along the chain until a handler (receiver3) handles it.
• The interaction starts with the Sender that calls handleRequest() on the receiver1 object (of type Handler).
• receiver1 forwards the request by calling handleRequest() on the receiver2 object.
• receiver2 forwards the request by calling handleRequest() on the receiver3 object.
• receiver3 handles the request and returns to receiver2 (which returns to receiver1, which in turn returns to the Sender).
• See also Sample Code / Example 1.