---
title: "Chain of Responsibility Design Pattern: Decoupling Complex Business Rules, One Handler at a Time"
url: https://daily.dev/posts/chain-of-responsibility-design-pattern-decoupling-complex-business-rules-one-handler-at-a-time-ugelj8czw
source_url: https://www.freecodecamp.org/news/chain-of-responsibility-design-pattern-decoupling-complex-business-rules
type: article
source: "freeCodeCamp"
published: 2026-08-21T23:15:31.932Z
updated: 2026-08-21T23:15:53.495Z
tags: ["architecture", "dart", "design-patterns"]
reading_time: 16
upvotes: 0
comments: 0
language: en
---

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# Chain of Responsibility Design Pattern: Decoupling Complex Business Rules, One Handler at a Time

**[freeCodeCamp](https://daily.dev/sources/freecodecamp)** · 16 min read · 0 upvotes · 0 comments

## Summary

An explanation of the Chain of Responsibility behavioral design pattern, showing how it decouples complex business rules by breaking them into independent, single-responsibility handlers linked in a chain. Two worked Dart examples illustrate the pattern: a fintech transaction approval flow (fraud, KYC, account status, approval tier checks) and a user onboarding validation flow (email, password, age, duplicate account checks). Includes full code, handler interfaces, chain construction, and sample output, along with guidance on when the pattern fits and when it doesn't.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://www.freecodecamp.org/news/chain-of-responsibility-design-pattern-decoupling-complex-business-rules>

## Questions this post answers

### When should I use the chain of responsibility pattern instead of a single validation function?

Use it when a request must pass through multiple independent checks whose number or order may change over time, and when each check should be independently testable. It is not worth the overhead for only one or two checks, when processing order is fixed forever, when handlers need to share results with each other, or when every handler must always run regardless of earlier outcomes.

_daily.dev surfaces pattern comparisons like this for developers deciding how to structure validation logic._

### How do you avoid a null pointer crash at the end of a chain of responsibility implementation?

Declare the reference to the next handler as nullable and check whether it is null before calling it, rather than assuming a next handler always exists. In a Dart implementation, the base handler class stores a nullable `_next` field and a `passToNext` helper method checks `if (_next != null)` before invoking `_next!.handle(request)`, logging or silently stopping when the chain ends.

_developers implementing handler chains in dart can reference concrete examples like this on daily.dev._

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---

Tags: [#architecture](https://daily.dev/tags/architecture), [#dart](https://daily.dev/tags/dart), [#design-patterns](https://daily.dev/tags/design-patterns)

[View this post on daily.dev](https://daily.dev/posts/chain-of-responsibility-design-pattern-decoupling-complex-business-rules-one-handler-at-a-time-ugelj8czw)