大话设计模式--职责连模式 Chain of Resposibility -- C++实现实例

1. 职责链模式： 使多个对象都有机会处理请求，从而避免请求发送者和接受者之间的耦合关系，将这个对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它。

当客户提交一个请求时，请求是沿着链传递直到有一个ConcreteHandler对象负责处理它，接收者和发送者都没有对方的明确信息，且链中的对象并不知道链的结构。

结果是职责链可以简化对象的互相连接，他们仅需一个指向其后继者的引用，而不需要保持它所有后继者的引用。

一个请求极有可能到了链的最末端还是得不到处理，或者没有正确配置而得不到处理，需要事先考虑全面。

实例：

handler.h handler.cpp

#ifndef HANDLER_H
#define HANDLER_H

class Handler
{
public:
    Handler();
    ~Handler();
    void setSuccessor(Handler *successor);
    void virtual handlerRequest(int request)=0;

protected:
    Handler *successor;
};

#endif // HANDLER_H

#include "handler.h"

Handler::Handler()
{
    successor = 0;
}

Handler::~Handler()
{
    delete successor;
}

void Handler::setSuccessor(Handler *successor)
{
    this->successor = successor;
}

concretehandler1.h concretehandler1.cpp

#ifndef CONCRETEHANDLER1_H
#define CONCRETEHANDLER1_H

#include "handler.h"

class ConcreteHandler1 : public Handler
{
public:
    ConcreteHandler1();
    void handlerRequest(int request);
};

#endif // CONCRETEHANDLER1_H

#include "concretehandler1.h"
#include <stdio.h>

ConcreteHandler1::ConcreteHandler1()
{
}

void ConcreteHandler1::handlerRequest(int request)
{
    if( request >=0 && request < 10 )
    {
        printf("ConcreteHandler1 handlerRequest\n");
    }
    else
    {
        if( successor!=0 )
        {
            printf("the next one handler\n");
            successor->handlerRequest(request);
        }
    }
}

concretehandler2.h concretehandler2.cpp

#ifndef CONCRETEHANDLER2_H
#define CONCRETEHANDLER2_H

#include "handler.h"

class ConcreteHandler2 : public Handler
{
public:
    ConcreteHandler2();
    void handlerRequest(int request);
};

#endif // CONCRETEHANDLER2_H

#include "concretehandler2.h"
#include <stdio.h>

ConcreteHandler2::ConcreteHandler2()
{
}

void ConcreteHandler2::handlerRequest(int request)
{
    if( request >=10 && request < 20 )
    {
        printf("ConcreteHandler2 handlerRequest\n");
    }
    else
    {
        if( successor!=0 )
        {
            printf("the next one handler\n");
            successor->handlerRequest(request);
        }
    }
}

main.cpp

#include <iostream>
#include "concretehandler1.h"
#include "concretehandler2.h"
using namespace std;

int main()
{
    cout << "Chain_of_responsibility test!" << endl;

    Handler *h1 = new ConcreteHandler1();
    Handler *h2 = new ConcreteHandler2();
    h1->setSuccessor(h2);
    h1->handlerRequest(15);

    return 0;
}