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。

//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