chain of responsibility - 对象行为型模式-优快云博客

本文深入探讨了责任链设计模式的原理与应用，通过实例代码展示了如何使多个对象有机会处理请求，避免发送者与接收者之间的直接耦合，形成一条处理请求的链，直至请求被处理。

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1.意图
使多个对象都有机会处理请求，从而避免发送者和接收者的耦合关系。将一些
对象连成一条链。并沿着这条链传递请求，直到有一个对象处理它为止
2.参与者
Handler -定义一个请求接口
-（可先）实现一个后继链
ConcreteHandler - 处理它所负责的请求
- 可访问它的后继者
Client - 向链上的具体处理者提交请求

3.结构

4.代码

public interface Handler {
	void handlerHelp(Request r);

	void next(Handler h);
}

public class Request {
	private String topic;
	private String content;

	public String getTopic() {
		return topic;
	}

	public void setTopic(String topic) {
		this.topic = topic;
	}

	public String getContent() {
		return content;
	}

	public void setContent(String content) {
		this.content = content;
	}

}

public class ConcreteHandlerA implements Handler {
	private List<String> topicList;
	private Handler nextHandler;

	ConcreteHandlerA() {
		topicList = new ArrayList<String>();
		topicList.add("A");
		topicList.add("B");
		topicList.add("C");
	}

	@Override
	public void handlerHelp(Request r) {
		String topic = r.getTopic();
		if (topic != null) {
			if (topicList.contains(topic)) {
				System.out.println("ConcreteHandlerA konw " + topic);
			}
		}
		if (nextHandler != null) {
			nextHandler.handlerHelp(r);
		}
	}

	@Override
	public void next(Handler h) {
		this.nextHandler = h;

	}

}

public class ConcreteHandlerB implements Handler {

	private List<String> topicList;
	private Handler nextHandler;

	ConcreteHandlerB() {
		topicList = new ArrayList<String>();
		topicList.add("D");
		topicList.add("E");
		topicList.add("F");
	}

	@Override
	public void handlerHelp(Request r) {
		String topic = r.getTopic();
		if (topic != null) {
			if (topicList.contains(topic)) {
				System.out.println("ConcreteHandlerB konw " + r.getContent());
			}
		}
		if (nextHandler != null) {
			nextHandler.handlerHelp(r);
		}
	}

	@Override
	public void next(Handler h) {
		this.nextHandler = h;

	}

}

public class ConcreteHandlerC implements Handler {

	private List<String> topicList;
	private Handler nextHandler;

	ConcreteHandlerC() {
		topicList = new ArrayList<String>();
		topicList.add("I");
		topicList.add("J");
		topicList.add("K");
	}

	@Override
	public void handlerHelp(Request r) {
		String topic = r.getTopic();
		if (topic != null) {
			if (topicList.contains(topic)) {
				System.out.println("ConcreteHandlerC konw " + topic+":"+r.getContent());
			}
		}
		if (nextHandler != null) {
			nextHandler.handlerHelp(r);
		}
	}

	@Override
	public void next(Handler h) {
		this.nextHandler = h;

	}

}


public class Client {
	public static void main(String[] args) {
		ConcreteHandlerA A =new ConcreteHandlerA();
		ConcreteHandlerB B =new ConcreteHandlerB();
		ConcreteHandlerC C =new ConcreteHandlerC();
		A.next(B);B.next(C);
		Request r = new Request();
		r.setTopic("H");
		r.setContent("hao are you!");
		A.handlerHelp(r);
	}
}