Chain of Responsibility(职责链)——对象行为型模式

      意图：使多个请求对象都有机会处理请求，从而避免请求对象的发送者和接收者之间的耦合关系。将这些请求对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

 

职责链模式典型结构图

 

      职责模式中ConcreteHandle将自己的后继对象（向下传递消息的对象）记录在自己的后继表中，当一个请求到来时，ConcreteHandle先会检查自己有没有匹配的处理程序，如果有就自己处理，否则就传递给他的后继。下面的实例程序中只是简化了一下，ConcreteHandle只是简单的检查看自己有没有后继，有的话将请求传递给后继进行处理，没有的话就自己处理。

示例代码：

class Handler{public:virtual ~Handler();virtual void HandleRequest() = 0;void setSuccessor(Handler* pSucc);Handler* GetSuccessor() const;protected:Handler();Handler(Handler* pSucc);private:Handler* m_pSuccessor;};Handler::Handler(){m_pSuccessor = NULL;}Handler::Handler(Handler* pSucc){m_pSuccessor = pSucc;}Handler::~Handler(){if (m_pSuccessor != NULL){delete m_pSuccessor;m_pSuccessor = NULL; cout << "~Handler" << endl;}}void Handler::setSuccessor(Handler* pSucc){m_pSuccessor = pSucc; }Handler* Handler::GetSuccessor() const{ return m_pSuccessor;}class ConcretHandlerA : public Handler{public:ConcretHandlerA();ConcretHandlerA(Handler* pSucc); ~ConcretHandlerA();void HandleRequest();};class ConcretHandlerB : public Handler{public:ConcretHandlerB();ConcretHandlerB(Handler* pSucc); ~ConcretHandlerB();void HandleRequest();};ConcretHandlerA::ConcretHandlerA(){}ConcretHandlerA::ConcretHandlerA(Handler* pSucc) :Handler(pSucc){}ConcretHandlerA::~ConcretHandlerA(){ cout << "~ConcretHandlerA" << endl;}void ConcretHandlerA::HandleRequest(){ if (this->GetSuccessor() != NULL){ this->GetSuccessor()->HandleRequest(); cout << "Handle request by successor!" << endl; }else{ cout << "No successor, I must be handle it" << endl; }}ConcretHandlerB::ConcretHandlerB(){}ConcretHandlerB::ConcretHandlerB(Handler* pSucc) :Handler(pSucc){}ConcretHandlerB::~ConcretHandlerB(){ cout << "~ConcretHandlerB" << endl;}void ConcretHandlerB::HandleRequest(){ if (this->GetSuccessor() != NULL){ this->GetSuccessor()->HandleRequest(); cout << "Handle request by successor!" << endl; }else{ cout << "No successor, I must be handle it" << endl; }}int _tmain(int argc, _TCHAR* argv[]){ Handler* pHandlerA = new ConcretHandlerA(); Handler* pHandlerB = new ConcretHandlerB(); pHandlerA->setSuccessor(pHandlerB); pHandlerA->HandleRequest(); if (pHandlerA != NULL){ delete pHandlerA; pHandlerA = NULL; }return 0;}