23.职责链模式--Chain of Responsibility

原文地址：/article/7840313.html

Chain of Responsibility模式：

Chain of Responsibility模式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。将这个对象连成一条链，并沿着这条链传递该请求，知道有一个对象处理它为止。

当客户提交一个请求时，请求时沿链传递直至有一个ConcreteHandler对象负责处理它。这就使得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并不知道链的结构。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收者的引用，这也就大大降低了耦合度了。对于客户端来说，可以随时的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。

Chain of Responsibility模式典型的结构图为：



Chain of Responsibility模式的实现代码如下：

//Handle.h
#ifndef _HANDLE_H_
#define _HANDLE_H_
class Handle
{
public:
virtual ~Handle();
virtual void HandleRequest() = 0;
void SetSuccessor(Handle* succ);
Handle* GetSuccessor();
protected:
Handle();
Handle(Handle* succ);
private:
Handle* _succ;
};

class ConcreteHandleA:public Handle
{
public:
ConcreteHandleA();
~ConcreteHandleA();
ConcreteHandleA(Handle* succ);
void HandleRequest();
protected:
private:
};

//Handle.cpp
#include "Handle.h"
#include <iostream>
using namespace std;
Handle::Handle()
{
_succ = 0;
}
Handle::~Handle()
{
delete _succ;
}
Handle::Handle(Handle* succ)
{
this->_succ = succ;
}
void Handle::SetSuccessor(Handle* succ)
{
_succ = succ;
}
Handle* Handle::GetSuccessor()
{
return _succ;
}
void Handle::HandleRequest()
{
}
ConcreteHandleA::ConcreteHandleA()
{
}
ConcreteHandleA::ConcreteHandleA(Handle* succ):Handle(succ)
{
}
ConcreteHandleA::~ConcreteHandleA()
{
}
void ConcreteHandleA::HandleRequest()
{
if (this->GetSuccessor() != 0)
{
cout<<"ConcreteHandleA 我把处理权给后继节点....."<<endl;
this->GetSuccessor()->HandleRequest();
}
else
{
cout<<"ConcreteHandleA 没有后继了，我必须自己处理...."<<endl;
}
}
ConcreteHandleB::ConcreteHandleB()
{
}
ConcreteHandleB::ConcreteHandleB(Handle* succ):Handle(succ)
{
}
ConcreteHandleB::~ConcreteHandleB()
{
}
void ConcreteHandleB::HandleRequest()
{
if (this->GetSuccessor() != 0)
{
cout<<"ConcreteHandleB 我把处理权给后继节点....."<<endl;
this->GetSuccessor()->HandleRequest();
}
else
{
cout<<"ConcreteHandleB 没有后继了，我必须自己处理...."<<endl;
}
}

//main.cpp
#include "Handle.h"
#include <iostream>
using namespace std;
int main(int argc,char* argv[])
{
Handle* h1 = new ConcreteHandleA();
Handle* h2 = new ConcreteHandleB();
h1->SetSuccessor(h2);
h1->HandleRequest();
return 0;
}