责任链模式

责任链(Chain of Responsibility)模式

意图：避免请求发送者与接收者耦合在一起，让多个对象都有可能接收请求，将这些对象连接成一条链，并且沿着这条链传递请求，直到有对象处理它为止。

主要解决：职责链上的处理者负责处理请求，客户只需要将请求发送到职责链上即可，无须关心请求的处理细节和请求的传递，所以职责链将请求的发送者和请求的处理者解耦了。

代码:

#include <iostream>
#include <string>
using namespace std;

// 请求类型
enum class RequestType
{
    REQ_HANDLE1,
    REQ_HANDLE2,
    REQ_HANDLE3
};

class Request
{
public:
    Request(string des, RequestType type) :_description(des), _reqType(type){}
    inline const string& getDescription() const { return _description; }
    inline RequestType getType() const { return _reqType; }
    void setType(const RequestType  type){ _reqType = type; }
private:
    string _description;   // 描述信息
    RequestType _reqType;  // 类型
};

class ChainHandler
{
private:
    void sendRequestToNextChain(const Request &req)
    {
        if (_nextChain != nullptr)
        {
            _nextChain->handle(req);
        }
    }

protected:
    virtual bool canHandleRequest(const Request &req) = 0;  // 判断能否处理请求
    virtual void processRequest(const Request &req) = 0;  // 处理请求

public:
    ChainHandler()
    {
        _nextChain = nullptr;
    }
　　 virtual ~ChainHandler() {}
    void setNextChain(ChainHandler *next) { _nextChain = next; }
    void handle(const Request &req)  // 接收请求
    {
        if (canHandleRequest(req))
            processRequest(req);
        else
          sendRequestToNextChain(req);
            
    }
private:
    ChainHandler *_nextChain;
};


class Handler1 : public ChainHandler
{
protected:
    virtual bool canHandleRequest(const Request &req)
    {
        return req.getType() == RequestType::REQ_HANDLE1;
    }

    virtual void processRequest(const Request &req) // 处理请求
    {
        cout << "Handler1 process request: " << req.getDescription() << endl;
    }

};

class Handler2 : public ChainHandler
{
protected:
    virtual bool canHandleRequest(const Request &req)
    {
        return req.getType() == RequestType::REQ_HANDLE2;
    }

    virtual void processRequest(const Request &req)
    {
        cout << "Handler2 process request: " << req.getDescription() << endl;
    }

};

class Handler3 : public ChainHandler
{
protected:
    virtual bool canHandleRequest(const Request &req)
    {
        return req.getType() == RequestType::REQ_HANDLE3;
    }

    virtual void processRequest(const Request &req)
    {
        cout << "Handler3 process request: " << req.getDescription() << endl;
    }

};

void test()
{
    Handler1 h1;
    Handler2 h2;
    Handler3 h3;
    h1.setNextChain(&h2);
    h2.setNextChain(&h3);
    Request req("produce car...", RequestType::REQ_HANDLE1);
    h1.handle(req);
    req.setType(RequestType::REQ_HANDLE2);
    h1.handle(req);
    req.setType(RequestType::REQ_HANDLE3);
    h1.handle(req);
}

int main()
{
    test();
    cin.get();
    return 0;
}

效果: