责任链模式

责任链模式(Chain of Responsibility)，使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这个对象连成一条链，并沿着这条链传递该请求，知道有一个对象处理它为止。

责任链模式的结构图

责任链模式中的角色：

• Handler：定义一个处理请示的接口
• ConcreteHandler：具体处理者类，处理它所负责的请求，可访问它的后继者，如果可处理该请求，就处理之，否则就将该请求转发给它的后继者。

责任链模式的简单实现

（1）处理请示的接口

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）具体处理者类

public class CommonManager extends Manager {

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

    @Override
    public void requestApplication(Request request) {
        if (request.getRequestType().equals("请假") && request.getNumber() <= 2) {
            System.out.println(name + ":" + request.getRequestContent() + "数量" + request.getNumber() + "被批准");
        } 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("请假") && request.getNumber() <= 5) {
            System.out.println(name + ":" + request.getRequestContent() + "数量" + request.getNumber() + "被批准");
        } 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("请假")) {
            System.out.println(name + ":" + request.getRequestContent() + "数量" + request.getNumber() + "被批准");
        } else if (request.getRequestType().equals("加薪") && request.getNumber() <= 500) {
            System.out.println(name + ":" + request.getRequestContent() + "数量" + request.getNumber() + "被批准");
        } else if (request.getRequestType().equals("加薪") && request.getNumber() > 500) {
            System.out.println(name + ":" + request.getRequestContent() + "数量" + request.getNumber() + "再说吧");
        }
    }
}

（3）客户端调用

public class Client {

    public static void main(String[] args) {
        CommonManager commonManager = new CommonManager("经理");
        Majordomo majordomo = new Majordomo("总监");
        GeneralManager generalManager = new GeneralManager("总经理");

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

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

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

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

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

    }
}

（4）输出

经理:yuzhiyi请假数量1被批准
总监:yuzhiyi请假数量4被批准
总经理:yuzhiyi请求加薪数量500被批准
总经理:yuzhiyi请求加薪数量1000再说吧

责任链模式的使用场景

使用场景：
当客户提交一个请求时，请求时沿链传递直至有一个 ConcreteHandler 对象负责处理它。

责任链的优缺点

优点：
接收者和发送者都没有对方的明确信息，且链中的对象自己也并不知道链的结构。结果是责任链可简化对象的相互连接，它们仅需保持一个指向其后继者的引用，而不需保持它所有的候选者的引用。
随时地增加或修改一个请求的结构。增强了给对象指派职责的灵活性。

缺点：
一个请求极有可能到了链的末端都得不到处理，或者因为没有正确配置而得不到处理。