Suggest an editImprove this articleRefine the answer for “In which cases is it appropriate to apply this pattern?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)The **Chain of Responsibility** pattern is appropriate when you need to **organize flexible, configurable request handling**, where **several objects could potentially handle it**, but it is not known in advance which one. **Key point:** the pattern is ideal for step-by-step, modular request handling, especially in validation, filtering, event handling, and middleware architecture.Shown above the full answer for quick recall.Answer (EN)ImageThe **Chain of Responsibility** pattern is appropriate when you need to **organize flexible, configurable request handling**, where **several objects could potentially handle it**, but it is not known in advance which one. --- ### 1. **When You Need to Split Processing Stages** If a request goes **through a series of checks or actions**, and each one performs its own piece of work (validation, logging, authorization, data processing). > *Example:* handling an HTTP request: logging -> authorization check -> validation -> controller. --- ### 2. **When Different Handlers for the Same Request Type Are Possible** If the handling logic **depends on conditions**, and you don't want to write bulky `if/else` or `switch` statements. > *Example:* different support levels in a helpdesk - agent -> manager -> director. --- ### 3. **When It's Important to Weaken Coupling Between Sender and Handlers** The sender does not know exactly who will handle the request - this allows **new handlers to be added easily**, without touching existing code. > *Example:* an event system: a module sends an event, and listeners (handlers) decide whether to react or not. --- ### 4. **When You Need to Allow Interrupting the Processing** If the chain's execution should stop as soon as a suitable handler is found. > *Example:* an authorization system: token check -> role check -> access granted -> chain interrupted. --- ### 5. **When Configurable or Dynamic Processing Is Required** The chain can be **changed at runtime** - handlers can be added, removed, or reordered. > *Example:* middleware in web frameworks (`Express.js`, `Spring`, `ASP.NET`), where each layer decides what to do with the request next. --- ### **Conclusion** Use **Chain of Responsibility** when: - a request can be handled by **different objects**; - you need to **get rid of rigid conditional constructs**; - it's important to **flexibly manage the order and composition of handlers**; - you need the ability to **interrupt the chain** at the right stage. **Summary:** The pattern is ideal for **step-by-step, modular request handling**, especially in **validation, filtering, event handling, and middleware architecture**.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.