设计模式——服务定位器模式（C++实现）

服务定位器模式

         服务定位器模式充分利用了缓存技术。在首次请求某个服务时，服务定位器在 JNDI 中查找服务，并缓存该服务对象。当再次请求相同的服务时，服务定位器会在它的缓存中查找，这样可以在很大程度上提高应用程序的性能。

以下是这种设计模式的实体。

             1、服务（Service） - 实际处理请求的服务。对这种服务的引用可以在 JNDI 服务器中查找到。

              2、Context / 初始的 Context - JNDI Context 带有对要查找的服务的引用。

              3、服务定位器（Service Locator） - 服务定位器是通过 JNDI 查找和缓存服务来获取服务的单点接触。

              4、缓存（Cache） - 缓存存储服务的引用，以便复用它们。

              5、客户端（Client） - Client 是通过 ServiceLocator 调用服务的对象。

采用菜鸟教程的例子，这里用C++实现

#include<iostream>
#include<string>
#include<list>

using namespace std;

//创建服务抽象接口类Service
class Service
{
public:
	Service() {};
	virtual ~Service() {};
	virtual string getName()=0;
	virtual void execute()=0;
};

//创建服务实体类Service1
class Service1 :public Service
{
public:
	Service1() {};
	~Service1() {};
	string getName();
	void execute();
};

string Service1::getName()
{
	return "service1";
}
void Service1::execute()
{
	cout << "execute Service1" << endl;
}

//创建服务实体类Service2
class Service2 :public Service
{
public:
	Service2() {};
	~Service2() {};
	string getName();
	void execute();
};

string Service2::getName()
{
	return "service2";
}
void Service2::execute()
{
	cout << "execute Service2" << endl;
}

//为 JNDI 查询创建 InitialContext。主要是负责对服务实体对象的管理
class InitialContext
{
public:
	InitialContext() {};
	~InitialContext() {};
	Service *lookup(string tname);
};


Service *InitialContext::lookup(string tname)
{
	if ("service1" == tname)
	{
		cout << "Looking up and creating a new Service1 object" << endl;
		return new Service1();
	}
	else if ("service2" == tname)
	{
		cout << "Looking up and creating a new Service2 object" << endl;
		return new Service2();
	}
	else
	{
		return NULL;
	}
}

//创建缓存类Cache
class Cache 
{
public:
	Cache() {};
	~Cache();

	Service* getService(string serviceName);
	void addService(Service *newService);
private:
	list<Service*> services;
};

Cache::~Cache()
{
	list<Service*>::iterator it;
	for (it = this->services.begin(); it != this->services.end(); ++it)
	{
		delete (*it);
		(*it) = NULL;
	}
}

Service* Cache::getService(string serviceName)
{
	list<Service*>::iterator it;
	for (it = this->services.begin(); it != this->services.end(); ++it)
	{
		if ((*it)->getName() == serviceName)
		{
			cout << "Returning cached: " << serviceName << " Object" << endl;
			return (*it);
		}
	}
	return NULL;
}
void Cache::addService(Service *newService)
{
	bool exits=false;
	list<Service*>::iterator it;
	for (it = this->services.begin(); it != this->services.end(); ++it)
	{
		if ((*it)->getName() == newService->getName())
		{
			exits = true;
		}
	}
	if (!exits)
	{
		this->services.push_back(newService);
	}
}

//创建服务定位器类ServiceLocator，获取具体的服务
class ServiceLocator
{
public:
	ServiceLocator() {};
	~ServiceLocator() {};
	static Service* getService(string sername);
private:
	static Cache tcache;
	static InitialContext inicontext;
};

Cache ServiceLocator::tcache;
InitialContext ServiceLocator::inicontext;

Service* ServiceLocator::getService(string sername)
{
	if (NULL != ServiceLocator::tcache.getService(sername))
	{
		return ServiceLocator::tcache.getService(sername);
	}
	else
	{
		ServiceLocator::tcache.addService(ServiceLocator::inicontext.lookup(sername));
		return ServiceLocator::inicontext.lookup(sername);
	}
}

int main()
{
	Service *service = ServiceLocator::getService("service1");
	service->execute();

	service = ServiceLocator::getService("service2");
	service->execute();

	service = ServiceLocator::getService("service1");
	service->execute();

	service = ServiceLocator::getService("service2");
	service->execute();

	delete service;
	service = NULL;
	system("pause");
	return 0;
}

在visual studio 2015上运行结果：