设计模式-责任链模式

责任链模式

模式定义

• 责任链模式属于行为型模式，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为止。

模式角色

• Handler 抽象类：处理请求对象的抽象类
• ConcreteHandler：处理请求的具体对象

UML 图

代码实例

#include <iostream>
using namespace std;

class Leader
{
public:
    void setNext(Leader* nextLeader){
        m_pstNextLeader = nextLeader;
    }

    Leader* getNext(){
        return m_pstNextLeader;
    }

    virtual ~Leader(){}
    virtual void handleRequest(int leaveDays) = 0;

private:
    Leader* m_pstNextLeader;
};

class ClassAdviser : public Leader
{
public:
    void handleRequest(int leaveDays){
        if(leaveDays <= 2) {
            cout << "ClassAdviser have permitted your holiday: " << leaveDays << endl;
        }
        else{
            if(getNext() != nullptr){
                getNext()->handleRequest(leaveDays);
            }
            else{
                cout << "Holiday is too big, and nobody can perimit" << endl;
            }
        }
    }
private:
};

class DepartmentHead : public Leader
{
public:
    void handleRequest(int leaveDays){
        if(leaveDays <= 7){
            cout << "DepartmentHead have permitted your holiady: " << leaveDays << endl;
        }
        else{
            if(getNext() != nullptr){
                getNext()->handleRequest(leaveDays);
            }
            else{
                cout << "Holiday is too big, and nobody can perimit" << endl;
            }
        }
    }
private:

};

class Dean : public Leader
{
public:
    void handleRequest(int leaveDays){
        if(leaveDays <= 10){
            cout << "Dean have permitted your holiady: " << leaveDays << endl;
        }
        else{
            if(getNext() != nullptr){
                getNext()->handleRequest(leaveDays);
            }
            else{
                cout << "Holiday is too big, and nobody can perimit" << endl;
            }
        }       
    }
private:

};

int main()
{
    Leader* pstClassAdviser = new ClassAdviser();
    Leader* pstDepartment = new DepartmentHead();
    Leader* pstDean = new Dean();

    pstClassAdviser->setNext(pstDepartment);
    pstDepartment->setNext(pstDean);

    int leaveDays[5] = {1, 5, 7, 10, 13};
    for(int i = 0; i < (int)(sizeof(leaveDays)/sizeof(leaveDays[0])); ++i){
        pstClassAdviser->handleRequest(leaveDays[i]);
    }

    return 0;
    
}

优缺点

优点：

1. 请求者与处理者的松耦合
2. 处理类对象的添加和删除不影响处理逻辑
3. 职责明确

缺点：

1. 请求不一定被处理
2. 责任链太长会影响系统性能
3. 责任链的设定依赖客户端，可靠性会受到客户端影响