Ensuring a Strong Chain of Responsibility: Key Steps

A strong Chain of Responsibility distributes transport safety duties across every party in the chain — operators, executives, consignors, loaders, and managers — so each handler checks, processes, or forwards responsibility without tight coupling. Building it requires a defined handler interface, a base handler for shared logic, concrete handlers for specific duties, and a client that assembles and initiates the chain.

The Chain of Responsibility is a behavioural design pattern that distributes a request across a sequence of handlers. Each handler decides whether to process the request or forward it to the next handler in the sequence. This decouples senders from receivers — the component that issues a request does not need to know which specific object will handle it.

In transport compliance, the same principle applies: daily fleet activity must connect back to duties, controls, and review. Each party in the chain carries specific obligations under the HVNL, which establishes that safety is a shared responsibility across all parties in the transport chain. Learn more about Chain of Responsibility obligations and the duties each party holds.

The pattern solves a specific problem: when multiple objects might handle a request, you need a way to distribute responsibility without tight coupling. Different handlers validate, authenticate, log, or route requests, and each performs specific checks or transformations.

Software systems often face requests that require multiple processing steps. Traditional approaches create tight coupling between request senders and receivers — the sender must know which receiver handles each request type. This knowledge scales poorly: adding new request types means updating sender logic, and changing handler assignments requires modifying multiple locations.

The Chain of Responsibility pattern solves these problems through indirection. The sender only knows about the chain's entry point, not individual handlers. Handlers determine routing based on their internal logic.

Dynamic handler composition

Chains support runtime configuration of handler sequences. You can:

• Add or remove handlers without changing client code
• Reorder handlers to match changing business rules
• Insert temporary handlers to intercept requests under specific conditions
• Build different handler sequences for different request types, all initiated through the same interface

This flexibility proves valuable for systems with evolving requirements. New validation steps can slot into existing chains, and conditional chain construction allows different request types to use different handler sequences. For transport operators, this means compliance controls can adapt as duties, vehicles, or freight types change without rewriting the entire system.

Building a handler chain follows a systematic process: start with interface design, build the base handler, implement concrete handlers, assemble the chain, and process requests.

Step 1: Define the handler interface

Identify the data that handlers need to process. Create a request object that encapsulates this data. Define the handler interface with two methods — handle for processing requests and setNext for linking handlers. Consider whether handlers should return values or use side effects like logging or state updates.

Step 2: Build the base handler

Implement the handler interface in an abstract base class. Store the next handler reference as a private field. Implement setNext to update this reference and return the handler instance for method chaining. Provide default handle behaviour that forwards to the next handler.

Step 3: Create concrete handlers

Extend the base handler for each specific processing responsibility. Override handle with custom logic, keeping each handler focused on a single responsibility. Decide whether each handler forwards requests after processing — pipeline-style handlers always forward, while selection-style handlers forward only when they cannot process the request.

Step 4: Assemble the chain

Instantiate concrete handler objects in the client code and link them together using setNext. Store a reference to the first handler — the client uses this reference to initiate request processing.

Step 5: Process requests

Call handle on the first handler to start processing. The handler chain manages the request flow automatically. Handle the response returned by the chain — some chains return null if no handler processed the request, while others guarantee a response.