职责链模式(Chain of Responsibility):使多个对象都有机会处理请求,从而避免请求的发送者和接收者之间的耦合关系。将这个对象连城一条链,并沿着这条链传递该请求,直到有一个对象处理它为止。【DP】
// ResponsbilityChain.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include <iostream>
using namespace std;
class Handler
{
protected:
Handler *successor;
public:
virtual ~Handler(){}
void SetSuccessor(Handler *successor)
{
this->successor = successor;
}
public:
virtual void HandleRequest(int request) = 0;
};
class ConcreteHandler1 : public Handler
{
public:
void HandleRequest(int request)
{
if (request >= 0 && request < 10)
{
cout << "ConcreteHandler1" << "处理请求" << request << endl;
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
}
};
class ConcreteHandler2 : public Handler
{
public:
void HandleRequest(int request)
{
if (request >= 10 && request < 20)
{
cout << "ConcreteHandler2" << "处理请求" << request << endl;
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
}
};
class ConcreteHandler3 : public Handler
{
public:
void HandleRequest(int request)
{
if (request >= 20 && request < 30)
{
cout << "ConcreteHandler2" << "处理请求" << request << endl;
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
}
};
int _tmain(int argc, _TCHAR* argv[])
{
Handler *h1 = new ConcreteHandler1;
Handler *h2 = new ConcreteHandler2;
Handler *h3 = new ConcreteHandler3;
h1->SetSuccessor(h2);//设置链条
h2->SetSuccessor(h3);
int requests[] = { 2, 5, 14, 22, 18, 3, 27, 20 };
for (int i = 0; i < sizeof(requests) / sizeof(int); ++i)
{
h1->HandleRequest(requests[i]);
}
return 0;
}
优点:
1.当客户提交一个请求时,请求是沿着链传递直到有一个ConcreteHandler对象处理它。【DP】
2.接收者和发送者都没有对方的明确信息,且链中的对象自己也不知道链的结构。结果是职责链可简化对象的相互连接,它们仅需保持一个指向其后继者的引用,而不需要保持它所有的候选接受者的引用。【DP】
3.随时地增加或修改处理一个请求的结构。增强了给对象指派职责的灵活性【DP】
缺点:一个请求极有可能到了链的末端都得不到处理,或者因为没有正确配置而得不到处理,这就很糟糕了,需要事先考虑周全。