责任链模式

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定义：使多个对象都有机会处理请求，从而避免了请求的发送者和接收者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有对象处理它为止。

类图：

其思想很简单，考虑员工要求加薪。公司的管理者一共有三级，总经理、总监、经理，如果一个员工要求加薪，应该向主管的经理申请，如果加薪的数量在经理的职权内，那么经理可以直接批准，否则将申请上交给总监。总监的处理方式也一样，总经理可以处理所有请求。这就是典型的职责链模式，请求的处理形成了一条链，直到有一个对象处理请求。给出这个例子的UML图。

class Manager  {  protected:      Manager *m_manager;      string m_name;  public:      Manager(Manager *manager, string name):m_manager(manager), m_name(name){}      virtual void DealWithRequest(string name, int num)  {}  };  class CommonManager: public Manager  {  public:      CommonManager(Manager *manager, string name):Manager(manager,name) {}      void DealWithRequest(string name, int num)       {          if(num < 500)         {              cout<<"Direct manager "<<m_name<<" approval "<<name<<" add salary "<<num<<" RMB"<<endl<<endl;          }          else          {              cout<<"Direct manager "<<m_name<<" will propost the request to majordomo"<<endl;              m_manager->DealWithRequest(name, num);          }      }  };  class Majordomo: public Manager  {  public:      Majordomo(Manager *manager, string name):Manager(manager,name) {}      void DealWithRequest(string name, int num)       {          if(num < 1000)          {              cout<<"majordomo "<<m_name<<" approval "<<name<<" add salary "<<num<<" RMB"<<endl<<endl;          }          else          {              cout<<"majordomo "<<m_name<<" will propost the request to the CEO"<<endl;              m_manager->DealWithRequest(name, num);          }      }  };  class GeneralManager: public Manager  {  public:      GeneralManager(Manager *manager, string name):Manager(manager,name) {}      void DealWithRequest(string name, int num)      {          cout<<"CEO "<<m_name<<" approval "<<name<<" add salary "<<num<<" RMB"<<endl<<endl;      }  }; int main()  {    cout<<"\n--------------start of the main()---------------"<<endl;    Manager *general = new GeneralManager(NULL, "A");      Manager *majordomo = new Majordomo(general, "B");      Manager *common = new CommonManager(majordomo, "C");      common->DealWithRequest("D",300);        common->DealWithRequest("E", 600);      common->DealWithRequest("F", 1000);      delete common; common = NULL;delete majordomo;majordomo = NULL;delete general;general = NULL;cout<<"\n--------------end of the main()---------------"<<endl;    return 0;  }

如果此时公司制度发生变化,我们只需要重新定义或者修改其中处于责任链上的某个对象，这样就实现了设计模式的解耦和单一职责等原则，便于系统的升级与维护。

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