責(zé)任鏈模式(Chain of Responsibility)，使多個對象都有機會處理請求，從而避免請求的發(fā)送者和接收者之間的耦合關(guān)系。將這個對象連成一條鏈，并沿著這條鏈傳遞該請求，知道有一個對象處理它為止。

責(zé)任鏈模式的結(jié)構(gòu)圖

責(zé)任鏈模式中的角色：

• Handler：定義一個處理請示的接口
• ConcreteHandler：具體處理者類，處理它所負責(zé)的請求，可訪問它的后繼者，如果可處理該請求，就處理之，否則就將該請求轉(zhuǎn)發(fā)給它的后繼者。

責(zé)任鏈模式的簡單實現(xiàn)

（1）處理請示的接口

public class Request {

    private String requestType;
    private String requestContent;
    private int number;

    public String getRequestType() {
        return requestType;
    }

    public void setRequestType(String requestType) {
        this.requestType = requestType;
    }

    public String getRequestContent() {
        return requestContent;
    }

    public void setRequestContent(String requestContent) {
        this.requestContent = requestContent;
    }

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }
}

public abstract class Manager {

    protected String name;
    protected Manager superior;

    public Manager(String name) {
        this.name = name;
    }

    public void setSuperior(Manager superior) {
        this.superior = superior;
    }

    public abstract void requestApplication(Request request);
}

（2）具體處理者類

public class CommonManager extends Manager {

    public CommonManager(String name) {
        super(name);
    }

    @Override
    public void requestApplication(Request request) {
        if (request.getRequestType().equals("請假") && request.getNumber() <= 2) {
            System.out.println(name + ":" + request.getRequestContent() + "數(shù)量" + request.getNumber() + "被批準");
        } else{
            if (superior != null) {
                superior.requestApplication(request);
            }
        }
    }
}

public class Majordomo extends Manager {

    public Majordomo(String name) {
        super(name);
    }

    @Override
    public void requestApplication(Request request) {
        if (request.getRequestType().equals("請假") && request.getNumber() <= 5) {
            System.out.println(name + ":" + request.getRequestContent() + "數(shù)量" + request.getNumber() + "被批準");
        } else{
            if (superior != null) {
                superior.requestApplication(request);
            }
        }
    }
}

public class GeneralManager extends Manager {

    public GeneralManager(String name) {
        super(name);
    }

    @Override
    public void requestApplication(Request request) {
        if (request.getRequestType().equals("請假")) {
            System.out.println(name + ":" + request.getRequestContent() + "數(shù)量" + request.getNumber() + "被批準");
        } else if (request.getRequestType().equals("加薪") && request.getNumber() <= 500) {
            System.out.println(name + ":" + request.getRequestContent() + "數(shù)量" + request.getNumber() + "被批準");
        } else if (request.getRequestType().equals("加薪") && request.getNumber() > 500) {
            System.out.println(name + ":" + request.getRequestContent() + "數(shù)量" + request.getNumber() + "再說吧");
        }
    }
}

（3）客戶端調(diào)用

public class Client {

    public static void main(String[] args) {
        CommonManager commonManager = new CommonManager("經(jīng)理");
        Majordomo majordomo = new Majordomo("總監(jiān)");
        GeneralManager generalManager = new GeneralManager("總經(jīng)理");

        commonManager.setSuperior(majordomo);
        majordomo.setSuperior(generalManager);

        Request request = new Request();
        request.setRequestType("請假");
        request.setRequestContent("yuzhiyi請假");
        request.setNumber(1);
        commonManager.requestApplication(request);

        Request request1 = new Request();
        request1.setRequestType("請假");
        request1.setRequestContent("yuzhiyi請假");
        request1.setNumber(4);
        commonManager.requestApplication(request1);

        Request request2 = new Request();
        request1.setRequestType("加薪");
        request1.setRequestContent("yuzhiyi請求加薪");
        request1.setNumber(500);
        commonManager.requestApplication(request1);

        Request request3 = new Request();
        request1.setRequestType("加薪");
        request1.setRequestContent("yuzhiyi請求加薪");
        request1.setNumber(1000);
        commonManager.requestApplication(request1);

    }
}

（4）輸出

經(jīng)理:yuzhiyi請假數(shù)量1被批準
總監(jiān):yuzhiyi請假數(shù)量4被批準
總經(jīng)理:yuzhiyi請求加薪數(shù)量500被批準
總經(jīng)理:yuzhiyi請求加薪數(shù)量1000再說吧

責(zé)任鏈模式的使用場景

使用場景：
當(dāng)客戶提交一個請求時，請求時沿鏈傳遞直至有一個 ConcreteHandler 對象負責(zé)處理它。

責(zé)任鏈的優(yōu)缺點

優(yōu)點：
接收者和發(fā)送者都沒有對方的明確信息，且鏈中的對象自己也并不知道鏈的結(jié)構(gòu)。結(jié)果是責(zé)任鏈可簡化對象的相互連接，它們僅需保持一個指向其后繼者的引用，而不需保持它所有的候選者的引用。
隨時地增加或修改一個請求的結(jié)構(gòu)。增強了給對象指派職責(zé)的靈活性。

缺點：
一個請求極有可能到了鏈的末端都得不到處理，或者因為沒有正確配置而得不到處理。