Chain of Responsibility Pattern

Chain of Responsibility Pattern에 대해 설명하는 페이지입니다.

Posted Dec 13, 2023

By HyunJinNo

Tags

Design Pattern, Java

1. Introduction

• Purpose
  • Gives more than one object an opportunity to handle a request by linking receiving objects together.
• Use When
  • Multiple objects may handle a request and the handler doesn't have to be a specific object.
  • A set of objects should be able to handle a request with the handler determined at runtime.
  • A request not being handled is an acceptable potential outcome.

2. Characteristics

• Each object in the chain receives the request and handles it or forwards it to the next object.
• Object making the request has no knowledge of which object is handling the request.
• The request has an implicit receiver.
• Each object in the chain shares a common interface for handling requests and accessing its successor on the chain.

3. Participants

• Handler
  • defines an interface for handling the requests
  • (optional) implements the successor link
• Concrete Handler
  • handles requests it it responsible for
  • can access its successor
  • if the Concrete Handler can handle the request, it does so; otherwise it forwards the request to its successor
• Client
  • initiates the request to a Concrete Handler object on the chain

4. Pros and Cons

• Benefits
  • Decoupling of senders and receivers
  • Added flexibility
  • Sender doesn't need to know specifically who the handlers are
• Potential Drawbacks
  • Client can't explicitly specify who handles a request
  • No guarantee of request being handled (request falls off end of chain)

5. How to Use (Example)

• Handler

  java

  1public abstract class Handler {
  2    protected Handler successor;
  3
  4    public void setSuccessor(Handler successor) {
  5        this.successor = successor;
  6    }
  7
  8    public abstract void handleRequest(int request);  // your request to be handled
  9}

• Concrete Handler

  java

  1public class ConcreteHandler1 extends Handler {
  2    @Override
  3    public void handleRequest(int request) {
  4        if (request >= 0 && request < 10) {
  5            System.out.println("ConcreteHandler1 handled request " + request);
  6        } else if (successor != null) {
  7            successor.handleRequest(request);
  8        }
  9    }
  10}

  java

  1public class ConcreteHandler2 extends Handler {
  2    @Override
  3    public void handleRequest(int request) {
  4        if (request >= 10 && request < 20) {
  5            System.out.println("ConcreteHandler2 handled request " + request);
  6        } else if (successor != null) {
  7            successor.handleRequest(request);
  8        }
  9    }
  10}

• Client

  java

  1public class Main {
  2    public static void main(String[] args) {
  3        Handler h1 = new ConcreteHandler1();
  4        Handler h2 = new ConcreteHandler2();
  5        h1.setSuccessor(h1);
  6
  7        int[] requests = new int[] { 5, 7, 13, 19, 20 };
  8
  9        for (int request : requests) {
  10            h1.handleRequest(request);
  11        }
  12    }
  13}