轉(zhuǎn)載自：
http://patmusing.blog.163.com/blog/static/13583496020101501114178/
在軟件構(gòu)建構(gòu)成中，一個(gè)請(qǐng)求可能被多個(gè)對(duì)象處理，但是每個(gè)請(qǐng)求在運(yùn)行時(shí)只能有一個(gè)接收者，如果顯示指定，將必不可少地帶來請(qǐng)求發(fā)送者與接收者的緊密耦合。COR(Chain of Reposibility)設(shè)計(jì)模式可以使請(qǐng)求的發(fā)送者不需要指定具體的接收者，讓請(qǐng)求的接收者自己在運(yùn)行時(shí)決定來處理請(qǐng)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(gè)對(duì)象都有機(jī)會(huì)處理請(qǐng)求，從而避免請(qǐng)求的發(fā)送者和接收者之間的耦合關(guān)系。將這些對(duì)象連成一條鏈，并沿著這條鏈傳遞請(qǐng)求，直到有一個(gè)對(duì)象對(duì)應(yīng)它為止。
其UML類圖如下：
C++示例代碼如下：
說明：
- 經(jīng)理級(jí)別可以決定是否采購500RMB以下的物品；
- 總監(jiān)級(jí)別可以決定是否采購5000RMB以下的物品；
- 總裁級(jí)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(jí)別可以決定購買任何價(jià)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(jié)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(jié)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。