设计模式之责任链模式(Chain of Responsibility Pattern)

港控/mmm° 2022-04-04 12:40 211阅读 0赞

*  责任链模式定义  
    责任链的重点是在“链”上，由一条链去处理相似的请求在链中决定谁来处理这个请求，并返回相应的结果。其定义为：Avoid coupling the sender of a request to its receiver by giving more than one project a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it. 使多个对象都有机会处理请求，从而避免了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，并沿着这条链传递改请求，直到有对象处理它为止。
 *  责任链模式通用类图  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdjaGVuZ21pbmcx_size_16_color_FFFFFF_t_70]
 *  责任链模式通用代码  
    首先是抽象处理者，①定义一个请求的处理方法handlerMessage。②定义一个链的编排方法。③定义具体的请求者必须实现的方法。

public abstract class Handler {
    
    	private Handler nextHandler;
    
    	@SuppressWarnings("unlikely-arg-type")
    	public final Response hanleMessage(Request request) {
    
    		Response response = null;
    
    		if (this.getHandlerLevel().equals(request.getRequestLevel())) {
    			response = this.echo(request);
    		} else {
    			if(this.nextHandler != null) {
    				response = this.nextHandler.hanleMessage(request);
    			}else {
    				
    			}
    		}
    		return response;
    	}
    
    	public void setNext(Handler _handler) {
    		this.nextHandler = _handler;
    	}
    
    	protected abstract Level getHandlerLevel();
    
    	protected abstract Response echo(Request request);
    }

public class Level {
    
    }
    
    public class Request {
    
    	public Level getRequestLevel() {
    		return null;
    	}
    }
    
    public class Response {
    
    }

具体的处理者1

public class ConcreteHandler1 extends Handler {
    
    	@Override
    	protected Level getHandlerLevel() {
    		// TODO Auto-generated method stub
    		return null;
    	}
    
    	@Override
    	protected Response echo(Request request) {
    		// TODO Auto-generated method stub
    		return null;
    	}
    }

具体的处理者2

public class ConcreteHandler2 extends Handler{
    
    	@Override
    	protected Level getHandlerLevel() {
    		// TODO Auto-generated method stub
    		return null;
    	}
    
    	@Override
    	protected Response echo(Request request) {
    		// TODO Auto-generated method stub
    		return null;
    	}
    }

具体的处理者3

public class ConcreteHandler3 extends Handler{
    
    	@Override
    	protected Level getHandlerLevel() {
    		// TODO Auto-generated method stub
    		return null;
    	}
    
    	@Override
    	protected Response echo(Request request) {
    		// TODO Auto-generated method stub
    		return null;
    	}
    }

调用类

public class Client {
    
    	public static void main(String[] args) {
    		
    		// 声明处理节点
    		Handler h1 = new ConcreteHandler1();
    		Handler h2 = new ConcreteHandler2();
    		Handler h3 = new ConcreteHandler3();
    		
    		// 处理顺序
    		h1.setNext(h2);
    		h1.setNext(h3);
    		
    		// 返回结果
    		Response response = h1.hanleMessage(new Request());
    	}
    }

*  责任链模式实例类图  
    其实责任链模式在我们工作中还是比较常见的，比如提交请假申请的流程就可以看做一个责任链模式，首先老大给批准，接下来经理批准，最后总监批准，这个过程就是一个链。  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdjaGVuZ21pbmcx_size_16_color_FFFFFF_t_70 1]
 *  责任链模式实例代码  
    首先是抽象处理者

public abstract class Handler {
    	/**
    	 * 持有下一个处理请求的对象
    	 */
    	protected Handler successor = null;
    
    	/**
    	 * 取值方法
    	 */
    	public Handler getSuccessor() {
    		return successor;
    	}
    
    	/**
    	 * 设置下一个处理请求的对象
    	 */
    	public void setSuccessor(Handler successor) {
    		this.successor = successor;
    	}
    
    	/**
    	 * @return 成功或失败的具体通知
    	 */
    	public abstract String handleRequest(String user, int dayNum);
    
    }

接下来分别是TeamLeader，Manager和GeneralManager

public class TeamLeader extends Handler {
    
    	@Override
    	public String handleRequest(String user, int dayNum) {
    
    		String str = "";
    		// TL权限比较小
    		if (dayNum < 3) {
    			if ("张三".equals(user)) {
    				str = "成功：TL同意【" + user + "】请假" + dayNum + "天";
    			} else {
    				// 其他人一律不同意
    				str = "其他人一律不同意";
    			}
    		} else {
    			// 请假超过三天的
    			if (getSuccessor() != null) {
    				return getSuccessor().handleRequest(user, dayNum);
    			}
    		}
    		return str;
    	}
    }

public class Manager extends Handler{
    
    	@Override
    	public String handleRequest(String user, int dayNum) {
    
    		String str = "";
    		// 经理权限相对较大
    		if (dayNum < 5) {
    			if ("张三".equals(user)) {
    				str = "成功：经理同意【" + user + "】请假" + dayNum + "天";
    			} else {
    				// 其他人一律不同意
    				str = "其他人一律不同意";
    			}
    		} else {
    			// 请假超过五天的
    			if (getSuccessor() != null) {
    				return getSuccessor().handleRequest(user, dayNum);
    			}
    		}
    		return str;
    	}
    
    }

public class GeneralManager extends Handler {
    
    	@Override
    	public String handleRequest(String user, int dayNum) {
    
    		String str = "";
    		// 总监权限最大
    		if (dayNum < 10) {
    			if ("张三".equals(user)) {
    				str = "成功：总监同意【" + user + "】请假" + dayNum + "天";
    			} else {
    				// 其他人一律不同意
    				str = "其他人一律不同意";
    			}
    		} else {
    			// 如果还有后继的处理对象，继续传递
    			if (getSuccessor() != null) {
    				return getSuccessor().handleRequest(user, dayNum);
    			}
    		}
    		return str;
    	}
    }

调用类

public class Client {
    
    	public static void main(String[] args) {
    
    		Handler h1 = new TeamLeader();
    		Handler h2 = new Manager();
    		Handler h3 = new GeneralManager();
    		
    		//开始测试
            String test1 = h1.handleRequest("张三", 2);
            System.out.println("test1 = " + test1);
            String test2 = h3.handleRequest("李四", 2);
            System.out.println("test2 = " + test2);
            System.out.println("---------------------------------------");
            
            String test3 = h2.handleRequest("张三", 4);
            System.out.println("test3 = " + test3);
            String test4 = h3.handleRequest("李四", 4);
            System.out.println("test4 = " + test4);
            System.out.println("---------------------------------------");
            
            String test5 = h3.handleRequest("张三", 7);
            System.out.println("test5 = " + test5);
            String test6 = h3.handleRequest("李四", 7);
            System.out.println("test6 = " + test6);
    	}
    
    }

输出结果

test1 = 成功：TL同意【张三】请假2天
    test2 = 其他人一律不同意
    ---------------------------------------
    test3 = 成功：经理同意【张三】请假4天
    test4 = 其他人一律不同意
    ---------------------------------------
    test5 = 成功：总监同意【张三】请假7天
    test6 = 其他人一律不同意

参考书籍：`设计模式之禅`  
实例代码放在[这里][Link 1]。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdjaGVuZ21pbmcx_size_16_color_FFFFFF_t_70]: /images/20220404/9d945353549c463d9d9690a420b6ed82.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdjaGVuZ21pbmcx_size_16_color_FFFFFF_t_70 1]: /images/20220404/4259238b5b0e4559af91b10304e3af00.png
[Link 1]: https://github.com/BazookaW/DesignPattern