责任链模式

雨点打透心脏的1/2处 2022-03-28 10:08 227阅读 0赞

责任链模式的定义：  
Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request.  
Chain the receiving objects and pass the request along the chaing until an object handles it;  
使用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受者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，  
知道有对象处理它为止。

![697878-20160512145707671-1257601599.png][]

//抽象处理者
    public abstract class Handler{
        private Handler nextHandler;
        public final Response handleMessage(Request request){
            Resonpse response=null;
            if(this.getHandlerLevel().equals(requset.getRequestLevel())){
                response=this.echo(request);
            }else{
                if(this.nextHandler !=null){
                    response=this.nextHandler.handleMessage(request);
                }else{
                    //.....
                }
            }
            return response;
        }
        public void setNext(Handler _handler){
            this.nextHandler=_handler;
        }
        protected abstract Level getHandlerLevel();
        protected abstract Response echo(Request request);
    }
    
    //具体处理者
    public class ConcreteHandler1 extends Handler{
        protected Response echo(Request request){
            return null;
        }
        protected Level getHandlerLevel(){
            return null;
        }
    }
    
    public class ConcreteHandler2 extends Handler{
        protected Response echo(Request request){
            return null;
        }
        protected Level getHandlerLevel(){
            return null;
        }
    }
    
    public class ConcreteHandler3 extends Handler{
        protected Response echo(Request request){
            return null;
        }
        protected Level getHandlerLevel(){
            return null;
        }
    }
    
    public class Level{}
    
    public class Request{}
    
    public class Response{}
    
    //场景类
    public class Client{
        public static void main(String[] args){
            Handler handler1=new ConcreteHanlder1();
            Handler handler2=new ConcreteHanlder2();
            Handler handler3=new ConcreteHanlder3();
            handler1.setNext(hanlder2);
            handler2.setNext(handler3);
            Response response=handler1.handlerMessage(new Request());
        }
    }

责任链模式优点：将请求和处理分开。请求者可以不用知道是谁处理的，处理者可以不用知道请求的全貌  
　　 缺点：一是性能问题，每个请求都是从链头遍历到链尾，特别是链比较长时，性能是一个非常大的问题  
　　　　　　　　二是调试不很方便，特别是链比较长时  
　　　　 注意事项：链中节点数量要控制，避免出现超长链的情况，一般的做法是在Handler中设置一个最大的节点数量，在setNext方法  
中判断是否已经超过其阈值，超过则不允许该链建立，避免无意识的破坏系统性能

[697878-20160512145707671-1257601599.png]: /images/20220328/e99fe3ed32a046128d5abfa11ae4fa4b.png