职责链模式ChainOfResponsibility

1.定义

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。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

2.结构图

Handler：定义职责的接口，通常在这里定义处理请求的方法，可以在这里实现后继链。
ConcreteHandler：实现职责的类，在这个类中，实现对在它职责范围内请求的处理，如果处理，就继续转发请求给后继者。
Client：职责链的客户端，向链上的具体处理对象提交请求，让职责链负责处理。

3.本质

职责链模式的本质：分离职责，动态组合。

4.Code Demo

Handler.java

package org.fool.cor;

public abstract class Handler {
    protected Handler successor;

    public void setSuccessor(Handler successor) {
        this.successor = successor;
    }

    public abstract void handleRequest();
}

ConcreteHandler1.java

package org.fool.cor;

public class ConcreteHandler1 extends Handler {
    @Override
    public void handleRequest() {
        boolean someCondition = false;

        if (someCondition) {
            System.out.println("ConcreteHandler1 invoked...");
        } else {
            if (successor != null) {
                successor.handleRequest();
            }
        }
    }
}

ConcreteHandler2.java

package org.fool.cor;

public class ConcreteHandler2 extends Handler {
    @Override
    public void handleRequest() {
        boolean someCondition = false;

        if (someCondition) {
            System.out.println("ConcreteHandler2 invoked...");
        } else {
            if (successor != null) {
                successor.handleRequest();
            }
        }
    }
}

ConcreteHandler3.java

package org.fool.cor;

public class ConcreteHandler3 extends Handler {
    @Override
    public void handleRequest() {
        boolean someCondition = true;

        if (someCondition) {
            System.out.println("ConcreteHandler3 invoked...");
        } else {
            if (successor != null) {
                successor.handleRequest();
            }
        }
    }
}

Client.java

package org.fool.cor;

public class Client {
    public static void main(String[] args) {
        Handler handler1 = new ConcreteHandler1();
        Handler handler2 = new ConcreteHandler2();
        Handler handler3 = new ConcreteHandler3();

        handler1.setSuccessor(handler2);
        handler2.setSuccessor(handler3);

        handler1.handleRequest();
    }
}

职责链模式ChainOfResponsibility

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