---
tags: Behavioral Patterns
---

# 責任鏈模式 Chain Of Responsibility

## 目的

把訊息傳給適合的class去做處理，否則就傳給下一個。
舉例：去送一個文件，但被Ａ窗口拒絕，並告知要去Ｂ窗口，接著又被Ｂ窗口拒絕後送去Ｃ窗口，這個文件才成功被處理。

## 架構圖


## 打武器 範例
* 打鐵 (機率提升攻擊)
* 鑲寶石 (機率提升特殊效果)
* 加把手 (機率提升命中)
* 取出 (出貨)

abstract class Handler {
    Handler nextHandler = null;
    public Handler(Handler nextHandler) {
        this.nextHandler = nextHandler;
    }
    public void execute() {
        action();
        if (nextHandler != null) {
            nextHandler.execute();
        }
    }
    abstract void action();
}
class ImproveAttackHandler extends Handler {
    public ImproveAttackHandler(Handler nextHandler) {
        super(nextHandler);
    }
    @Override
    void action() {
        System.out.println("Improve attack ability");
    }
}
class HitsRateHandler extends Handler {
    public HitsRateHandler(Handler nextHandler) {
        super(nextHandler);
    }
    @Override
    void action() {
        System.out.println("Improve hits rate ability");
    }
}
class SpecialAbilityHandler extends Handler {
    public SpecialAbilityHandler(Handler nextHandler) {
        super(nextHandler);
    }
    @Override
    void action() {
        System.out.println("Add special ability");
    }
}
class FinishHandler extends Handler {
    public FinishHandler(Handler nextHandler) {
        super(nextHandler);
    }
    @Override
    void action() {
        System.out.println("Take out weapon from smithy");
    }
}
public class ChainOfResponsibility {
    public static void main(String[] args) {
        System.out.println("Start to make a weapon");
        Handler handler = new ImproveAttackHandler(
                new SpecialAbilityHandler(
                        new HitsRateHandler(
                                new FinishHandler(null)
                        )
                )
        );
        handler.execute();
    }
}

## 範例1

// 所有處理郵件的子類別要繼承的介面
public abstract class MailHandler {

    // 每個處理郵件類別都要記錄下一個
    // 能處理的人是誰
    protected MailHandler mHandler;

    public MailHandler(MailHandler handler) {
        mHandler = handler;
    }

    public void toNext(Mail mail) {
        if(mHandler != null) {
            mHandler.handleMail(mail);
        } else {
            // 沒有後繼者, 表示是尾端了
            // 通常可以用最一般化的處理
        }
    }

    public abstract void handleMail(Mail mail);
}

public class SpamMailHandler extends MailHandler {
		SpamMailHandler(MailHandler handler){
				super(handler);
		}
    @Override
    public void handleMail(Mail mail) {
        // 假設已經能知道郵件分類了
        if(mail.isSpam()) {
            // 處理垃圾信
        } else {
            toNext(mail);
        }
    }
}

public class ThankMailHandler extends MailHandler {
        // 假設已經能知道郵件分類了
        if(mail.isThank()) {
            // 處理感謝信
        } else {
            toNext(mail);
        }
}
public class ComplainMailHandler extends MailHandler {
        // 假設已經能知道郵件分類了
        if(mail.isComplain()) {
            // 處理Complain
        } else {
            toNext(mail);
        }
}
public class GeneralMailHandler extends MailHandler {
      if(mail.isGeneral()) {
            // 處理General
        } else {
            toNext(mail);
        }
}
public class Main {

	public static void main(String[] args) {
		// 可以這樣使用
		MailHandler handler = new ThankMailHandler(
		                      new ComplainMailHandler(
		                      new SpamMailHandler(
		                      new GeneralMailHandler(null))));
		// 假設有一封郵件要處理
		Mail mail = new Mail(...);
		handler.hanldeMail(mail);
  }
}

## 範例2

public abstract class Support {
    private String name;                    // 問題解決者的名稱
    private Support next;                   // 轉送位置
    public Support(String name) {           // 產生問題解決者
        this.name = name;
    }
    public Support setNext(Support next) {  // 設定轉送位置
        this.next = next;
        return next;
    }
    public final void support(Trouble trouble) {  // 解決問題的步驟
        if (resolve(trouble)) {
            done(trouble);
        } else if (next != null) {
            next.support(trouble);
        } else {
            fail(trouble);
        }
    }
    public String toString() {              // 列印字串
        return "[" + name + "]";
    }
    protected abstract boolean resolve(Trouble trouble); // 解決的方法
    protected void done(Trouble trouble) {  // 已解決
        System.out.println(trouble + " is resolved by " + this + ".");
    }
    protected void fail(Trouble trouble) {  // 尚未解決
        System.out.println(trouble + " cannot be resolved.");
    }
}

public class SpecialSupport extends Support {
    private int number;                                 // 只能解決此號碼的問題
    public SpecialSupport(String name, int number) {    // 建構子
        super(name);
        this.number = number;
    }
    protected boolean resolve(Trouble trouble) {     // 解決的方法
        if (trouble.getNumber() == number) {
            return true;
        } else {
            return false;
        }
    }
}
public class OddSupport extends Support {
    public OddSupport(String name) {                // 建構子
        super(name);
    }
    protected boolean resolve(Trouble trouble) {    // 解決的方法
        if (trouble.getNumber() % 2 == 1) 
            return true;
        } else {
            return false;
        }
    }
}

public class NoSupport extends Support {
    public NoSupport(String name) {
        super(name);
    }
    protected boolean resolve(Trouble trouble) {     // 解決的方法
        return false; // 自己不做處理
    }
}
public class LimitSupport extends Support {
    private int limit;                              // 若小於此號碼則可解決問題
    public LimitSupport(String name, int limit) {   // 建構子
        super(name);
        this.limit = limit;
    }
    protected boolean resolve(Trouble trouble) {         // 解決的方法
        if (trouble.getNumber() < limit) {
            return true;
        } else {
            return false;
        }
    }
}
public class Trouble {
    private int number;             // 問題編號
    public Trouble(int number) {    // 發生問題
        this.number = number;
    }
    public int getNumber() {        // 取得問題編號
        return number;
    }
    public String toString() {      // 列印顯示問題的字串
        return "[Trouble " + number + "]";
    }
}
public class Main {
    public static void main(String[] args) {
        Support alice   = new NoSupport("Alice");
        Support bob     = new LimitSupport("Bob", 100);
        Support charlie = new SpecialSupport("Charlie", 429);
        Support diana   = new LimitSupport("Diana", 200);
        Support elmo    = new OddSupport("Elmo");
        Support fred    = new LimitSupport("Fred", 300);
        // 形成連鎖
        alice.setNext(bob).setNext(charlie).setNext(diana).setNext(elmo).setNext(fred);
        // 發生各種問題
        for (int i = 0; i < 500; i += 33) {
            alice.support(new Trouble(i));
        }
    }
}