轉載自：
http://patmusing.blog.163.com/blog/static/13583496020101501114178/
在軟件構建構成中，一個請求可能被多個對象處理，但是每個請求在運行時只能有一個接收者，如果顯示指定，將必不可少地帶來請求發送者與接收者的緊密耦合。COR(Chain of Reposibility)設計模式可以使請求的發送者不需要指定具體的接收者，讓請求的接收者自己在運行時決定來處理請求，從而使兩者解耦。
“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 chain until an object handles it.” - GoF
使多個對象都有機會處理請求，從而避免請求的發送者和接收者之間的耦合關系。將這些對象連成一條鏈，并沿著這條鏈傳遞請求，直到有一個對象對應它為止。
其UML類圖如下：
C++示例代碼如下：
說明：
- 經理級別可以決定是否采購500RMB以下的物品；
- 總監級別可以決定是否采購5000RMB以下的物品；
- 總裁級別可以決定是否采購任何物品。
// COR.h
#include <string>
#include <iostream>
#include <memory>
using namespace std;
// 消息類
class CORMessage
{
private:
double price;
public:
CORMessage(double price) : price(price)
{
}
double get_price()
{
return price;
}
};
// 抽象類Handler
class Handler
{
protected:
//Handler *next_handler;
auto_ptr<Handler> next_handler;
public:
//Handler(Handler *next_handler) : next_handler(next_handler)
Handler(auto_ptr<Handler> next_handler) : next_handler(next_handler)
{
}
virtual void handleMessage(CORMessage cor_message) = 0;
virtual bool canHandleMessage(CORMessage cor_message) = 0;
public:
virtual ~Handler()
{
cout << "in the destructor of Handler..." << endl;
}
};
// 具體處理類
class ConcreteManagerHandler : public Handler
{
public:
//ConcreteManagerHandler(Handler *next_handler) : Handler(next_handler)
ConcreteManagerHandler(auto_ptr<Handler> next_handler) : Handler(next_handler)
{
}
~ConcreteManagerHandler()
{
cout << "in the destructor of ConcreteManagerHandler..." << endl;
}
public:
void handleMessage(CORMessage cor_message)
{
if(canHandleMessage(cor_message))
{
cout << "MESSAGE IS HANDLED SUCCESSFULLY! -- ConcreteManagerHandler" << endl;
}
else
{
next_handler->handleMessage(cor_message);
}
}
bool canHandleMessage(CORMessage cor_message)
{
if(cor_message.get_price() < 500.0)
return true;
else
return false;
}
};
// 具體處理類
class ConcreteDirectorHandler : public Handler
{
public:
//ConcreteDirectorHandler(Handler *next_handler) : Handler(next_handler)
ConcreteDirectorHandler(auto_ptr<Handler> next_handler) : Handler(next_handler)
{
}
~ConcreteDirectorHandler()
{
cout << "in the destructor of ConcreteDirectorHandler..." << endl;
}
public:
void handleMessage(CORMessage cor_message)
{
if(canHandleMessage(cor_message))
{
cout << "MESSAGE IS HANDLED SUCCESSFULLY! -- ConcreteDirectorHandler" << endl;
}
else
{
next_handler->handleMessage(cor_message);
}
}
bool canHandleMessage(CORMessage cor_message)
{
if(cor_message.get_price() < 5000.0)
return true;
else
return false;
}
};
// 具體處理類
class ConcreteOfficerHandler : public Handler
{
public:
//ConcreteOfficerHandler(Handler *next_handler) : Handler(next_handler)
ConcreteOfficerHandler(auto_ptr<Handler> next_handler) : Handler(next_handler)
{
}
~ConcreteOfficerHandler()
{
cout << "in the destructor of ConcreteOfficerHandler..." << endl;
}
public:
void handleMessage(CORMessage cor_message)
{
if(canHandleMessage(cor_message))
{
cout << "MESSAGE IS HANDLED SUCCESSFULLY! -- ConcreteOfficerHandler" << endl;
}
else
{
next_handler->handleMessage(cor_message);
}
}
bool canHandleMessage(CORMessage cor_message)
{
return true; // 總裁級別可以決定購買任何價格的物品
}
};
// COR.cpp
#include "COR.h"
int main(int argc, char **argv)
{
//Handler *officer_handler = new ConcreteOfficerHandler(0);
//Handler *director_handler = new ConcreteDirectorHandler(officer_handler);
//Handler *manager_handler = new ConcreteManagerHandler(director_handler);
auto_ptr<Handler> officer_handler(new ConcreteOfficerHandler((auto_ptr<Handler>)0));
auto_ptr<Handler> director_handler(new ConcreteDirectorHandler(officer_handler));
auto_ptr<Handler> manager_handler(new ConcreteManagerHandler(director_handler));
manager_handler->handleMessage(CORMessage(350.0));
manager_handler->handleMessage(CORMessage(600.0));
manager_handler->handleMessage(CORMessage(10000.11));
//delete officer_handler;
//delete director_handler;
//delete manager_handler;
return 0;
}
輸出結果：
MESSAGE IS HANDLED SUCCESSFULLY! -- ConcreteManagerHandler
MESSAGE IS HANDLED SUCCESSFULLY! -- ConcreteDirectorHandler
MESSAGE IS HANDLED SUCCESSFULLY! -- ConcreteOfficerHandler
in the destructor of ConcreteManagerHandler...
in the destructor of Handler...
in the destructor of ConcreteDirectorHandler...
in the destructor of Handler...
in the destructor of ConcreteOfficerHandler...
in the destructor of Handler...
從輸出結果可見，
購買350.0RMB的物品被ConcreteManagerHandler處理了；
購買600.0RMB的物品被ConcreteDirectorHandler處理了；
購買10000.11RMB的物品被ConcreteOfficerHandler處理了。
注：如果不使用auto_ptr，則可以用被注釋的代碼部分代替。