行为型模式 --- 责任链模式

package study.org;

public class Demo {
    public static void main(String[] args) {
        // 组装责任链
        Handler handler1 = new ConcreteHandler1();
        Handler handler2 = new ConcreteHandler2();
        Handler handler3 = new ConcreteHandler3();
        handler2.setNext(handler3);
        handler1.setNext(handler2);
        
        // 提交请求
        handler1.operation("ConcreteHandler2");
    }
}

abstract class Handler {
    private Handler next;

    public Handler getNext() {
        return next;
    }

    public void setNext(Handler next) {
        this.next = next;
    }

    abstract void operation(String tail);
}

class ConcreteHandler1 extends Handler {

    @Override
    void operation(String tail) {
        if ("ConcreteHandler1".equals(tail)) {
            System.out.println("ConcreteHandler1 finish");
        } else {
            if (null != getNext()) {
                System.out.println("ConcreteHandler1 next->");
                getNext().operation(tail);
            } else {
                System.out.println("ConcreteHandler1 nothing! or error");
            }
        }
    }
}

class ConcreteHandler2 extends Handler {

    @Override
    void operation(String tail) {
        if ("ConcreteHandler2".equals(tail)) {
            System.out.println("ConcreteHandler2 finish");
        } else {
            if (null != getNext()) {
                System.out.println("ConcreteHandler2 next->");
                getNext().operation(tail);
            } else {
                System.out.println("ConcreteHandler2 nothing! or error");
            }
        }
    }
}

class ConcreteHandler3 extends Handler {

    @Override
    void operation(String tail) {
        if ("ConcreteHandler3".equals(tail)) {
            System.out.println("ConcreteHandler3 finish");
        } else {
            if (null != getNext()) {
                System.out.println("ConcreteHandler3 next->");
                getNext().operation(tail);
            } else {
                System.out.println("ConcreteHandler3 nothing! or error");
            }
        }
    }
}