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; }