14) chain of responsibility pattern

类别：

 behavioral pattern

问题：

 高耦合，不灵活

if(){

}else if(){

}else if(){

}
...

方案：

示例：

public class ChainOfResponsibilityPattern {

    public static void main(String[] args) {
        // 灵活装配
        Pipeline node1 = new Node1(1);
        Pipeline node2 = new Node2(2);
        Pipeline node3 = new Node3(3);
        node1.setNextNode(node2);
        node2.setNextNode(node3);

        // 固定用法
        node1.load(new Message(2, "need be handled by node2"));
        node1.load(new Message(1, "need be handled by node1"));
        node1.load(new Message(3, "need be handled by node3"));
    }

}

abstract class Pipeline {
    protected int level;
    // next element in chain or responsibility
    protected Pipeline nextNode;

    public void setNextNode(Pipeline nextNode) {
        if (nextNode == null) {
            throw new IllegalArgumentException("");
        }
        this.nextNode = nextNode;
    }

    public void load(Message msg) {
        if (msg == null) {
            throw new IllegalArgumentException("message not be null");
        }
        if (this.level == msg.getLevel()) {
            process(msg.getMsg());
        } else if (this.nextNode != null) {
            nextNode.load(msg);
        } else {
            // the last node can not handle the message
            throw new IllegalStateException("can not handle the message");
        }
    }

    abstract protected void process(String message);
}

class Node1 extends Pipeline {
    public Node1(int level) {
        this.level = level;
    }

    @Override
    protected void process(String message) {
        System.out.println("done by node1: " + message);
    }
}

class Node2 extends Pipeline {
    public Node2(int level) {
        this.level = level;
    }

    @Override
    protected void process(String message) {
        System.out.println("done by node2: " + message);
    }
}

class Node3 extends Pipeline {
    public Node3(int level) {
        this.level = level;
    }

    @Override
    protected void process(String message) {
        System.out.println("done by node3: " + message);
    }
}

class Message {
    private int level;
    private String msg;

    public Message(int level, String msg) {
        this.level = level;
        this.msg = msg;
    }

    public int getLevel() {
        return level;
    }

    public String getMsg() {
        return msg;
    }
}

done by node2: need be handled by node2
done by node1: need be handled by node1
done by node3: need be handled by node3

应用：

不足：(

优化：）