java-design-patterns/chain/README.md

---
layout: pattern
title: Chain of responsibility
folder: chain
permalink: /patterns/chain/
pumlid: 9SR13SCm20NGLTe1OkxTXX0KKzd4Wa-pVYlrdTxJN4OTMZ4U7LZv8Wg-ssdejLTgoELGHvDhaesw6HpqvWzlXwQTlYq6D3nfSlv2qjcS5F9VgvXjrHnV
categories: Behavioral
tags:
 - Java
 - Gang Of Four
 - Difficulty-Intermediate
---

## Intent
Avoid coupling the sender of a request to its receiver by giving
more than one object a chance to handle the request. Chain the receiving
objects and pass the request along the chain until an object handles it.

![alt text](./etc/chain_1.png "Chain of Responsibility")

## Applicability
Use Chain of Responsibility when

* more than one object may handle a request, and the handler isn't known a priori. The handler should be ascertained automatically
* you want 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

## Real world examples

* [java.util.logging.Logger#log()](http://docs.oracle.com/javase/8/docs/api/java/util/logging/Logger.html#log%28java.util.logging.Level,%20java.lang.String%29)
* [Apache Commons Chain](https://commons.apache.org/proper/commons-chain/index.html)
* [javax.servlet.Filter#doFilter()](http://docs.oracle.com/javaee/7/api/javax/servlet/Filter.html#doFilter-javax.servlet.ServletRequest-javax.servlet.ServletResponse-javax.servlet.FilterChain-)

## Credits

* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)