Цепочка обязанностей

Шаблон проектирования

поведенческий
Chain of responsibility
Тип:	поведенческий
Назначение:	для организации в системе уровней ответственности
Родственные шаблоны:	Компоновщик
Описан в Design Patterns	Да

Цепочка обязанностей — поведенческий шаблон проектирования, предназначенный для организации в системе уровней ответственности.

Применение

Шаблон рекомендован для использования в условиях:

• в разрабатываемой системе имеется группа объектов, которые могут обрабатывать сообщения определенного типа;
• все сообщения должны быть обработаны хотя бы одним объектом системы;
• сообщения в системе обрабатываются по схеме «обработай сам либо перешли другому», то есть одни сообщения обрабатываются на том уровне, где они получены, а другие пересылаются объектам иного уровня.

Примеры

Пример на PHP5

Исходный текст на PHP5.3

namespace ChainOfResponsibility {
 
    abstract class Logger {
 
        const ERR = 3;
        const NOTICE = 5;
        const DEBUG = 7;
 
        protected $mask;
        // The next element in the chain of responsibility
        protected $next;
 
        public function __construct($mask) {
            $this->mask = $mask;
        }
 
        public function setNext(Logger $log) {
            $this->next = $log;
            return $log;
        }
 
        public function message($msg, $priority) {
            if ($priority <= $this->mask) {
                $this->writeMessage($msg);
            }
 
            if ($this->next != null) {
                $this->next->message($msg, $priority);
            }
        }
 
        protected abstract function writeMessage($msg);
    }
 
    class StdoutLogger extends Logger {
 
        protected function writeMessage($msg) {
            echo sprintf("Writing to stdout: %s\n", $msg);
        }
 
    }
 
    class EmailLogger extends Logger {
 
        protected function writeMessage($msg) {
            echo sprintf("Sending via email: %s\n", $msg);
        }
 
    }
 
    class StderrLogger extends Logger {
 
        protected function writeMessage($msg) {
            echo sprintf("Sending to stderr: %s\n", $msg);
        }
 
    }
 
    //цепочка обязанностей
    class ChainOfResponsibilityExample {
        public function run() {
 
            // строим цепочку обязанностей
            $logger = new StdoutLogger(Logger::DEBUG);
            $logger1 = $logger->setNext(new EmailLogger(Logger::NOTICE));
            $logger2 = $logger1->setNext(new StderrLogger(Logger::ERR));
 
            // Handled by StdoutLogger and StdoutLogger
            $logger->message("Entering function y.", Logger::DEBUG);
 
            // Handled by StdoutLogger and EmailLogger
            $logger->message("Step1 completed.", Logger::NOTICE);
 
            // Handled by all three loggers
            $logger->message("An error has occurred.", Logger::ERR);
        }
    }
 
    $chain = new ChainOfResponsibilityExample();
    $chain->run();
 
}

Пример на Java

Исходный текст на Java

package chainofresp;
 
abstract class Logger {
    public static int ERR = 3;
    public static int NOTICE = 5;
    public static int DEBUG = 7;
    protected int mask;
 
    // The next element in the chain of responsibility
    protected Logger next;
 
    public Logger setNext(Logger log) {
        next = log;
        return log;
    }
 
    public void message(String msg, int priority) {
        if (priority <= mask) {
            writeMessage(msg);
        }
        if (next != null) {
            next.message(msg, priority);
        }
    }
 
    abstract protected void writeMessage(String msg);
}
 
class StdoutLogger extends Logger {
    public StdoutLogger(int mask) { 
        this.mask = mask;
    }
 
    protected void writeMessage(String msg) {
        System.out.println("Writing to stdout: " + msg);
    }
}
 
 
class EmailLogger extends Logger {
    public EmailLogger(int mask) {
        this.mask = mask;
    }
 
    protected void writeMessage(String msg) {
        System.out.println("Sending via email: " + msg);
    }
}
 
class StderrLogger extends Logger {
    public StderrLogger(int mask) {
        this.mask = mask;
    }
 
    protected void writeMessage(String msg) {
        System.err.println("Sending to stderr: " + msg);
    }
}
 
public class ChainOfResponsibilityExample {
    public static void main(String[] args) {
        // Build the chain of responsibility
        Logger logger, logger1,logger2;
        logger = new StdoutLogger(Logger.DEBUG);
        logger1 = logger.setNext(new EmailLogger(Logger.NOTICE));
        logger2 = logger1.setNext(new StderrLogger(Logger.ERR));
 
        // Handled by StdoutLogger
        logger.message("Entering function y.", Logger.DEBUG);
 
        // Handled by StdoutLogger and EmailLogger
        logger.message("Step1 completed.", Logger.NOTICE);
 
        // Handled by all three loggers
        logger.message("An error has occurred.", Logger.ERR);
    }
}
/*
The output is:
   Writing to stdout:   Entering function y.
   Writing to stdout:   Step1 completed.
   Sending via e-mail:  Step1 completed.
   Writing to stdout:   An error has occurred.
   Sending via e-mail:  An error has occurred.
   Writing to stderr:   An error has occurred.
*/
[edit]

Пример на C#

Исходный текст на языке C#

// Chain of Responsibility pattern -- Structural example
 
using System;
 
namespace DoFactory.GangOfFour.Chain.Structural
{
  /// <summary>
  /// MainApp startup class for Structural
  /// Chain of Responsibility Design Pattern.
  /// </summary>
  class MainApp
  {
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
      // Setup Chain of Responsibility
      Handler h1 = new ConcreteHandler1();
      Handler h2 = new ConcreteHandler2();
      Handler h3 = new ConcreteHandler3();
      h1.SetSuccessor(h2);
      h2.SetSuccessor(h3);
 
      // Generate and process request
      int[] requests = { 2, 5, 14, 22, 18, 3, 27, 20 };
 
      foreach (int request in requests)
      {
        h1.HandleRequest(request);
      }
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
  /// <summary>
  /// The 'Handler' abstract class
  /// </summary>
  abstract class Handler
  {
    protected Handler successor;
 
    public void SetSuccessor(Handler successor)
    {
      this.successor = successor;
    }
 
    public abstract void HandleRequest(int request);
  }
 
  /// <summary>
  /// The 'ConcreteHandler1' class
  /// </summary>
  class ConcreteHandler1 : Handler
  {
    public override void HandleRequest(int request)
    {
      if (request >= 0 && request < 10)
      {
        Console.WriteLine("{0} handled request {1}",
          this.GetType().Name, request);
      }
      else if (successor != null)
      {
        successor.HandleRequest(request);
      }
    }
  }
 
  /// <summary>
  /// The 'ConcreteHandler2' class
  /// </summary>
  class ConcreteHandler2 : Handler
  {
    public override void HandleRequest(int request)
    {
      if (request >= 10 && request < 20)
      {
        Console.WriteLine("{0} handled request {1}",
          this.GetType().Name, request);
      }
      else if (successor != null)
      {
        successor.HandleRequest(request);
      }
    }
  }
 
  /// <summary>
  /// The 'ConcreteHandler3' class
  /// </summary>
  class ConcreteHandler3 : Handler
  {
    public override void HandleRequest(int request)
    {
      if (request >= 20 && request < 30)
      {
        Console.WriteLine("{0} handled request {1}",
          this.GetType().Name, request);
      }
      else if (successor != null)
      {
        successor.HandleRequest(request);
      }
    }
  }
}
 
Output
ConcreteHandler1 handled request 2
ConcreteHandler1 handled request 5
ConcreteHandler2 handled request 14
ConcreteHandler3 handled request 22
ConcreteHandler2 handled request 18
ConcreteHandler1 handled request 3
ConcreteHandler3 handled request 27
ConcreteHandler3 handled request 20

Пример на C++

Исходный текст на языке C++

#include <iostream>
 
class Colleague;
 
class Mediator
{
public:
        virtual void Send(std::string message, Colleague *colleague)=0;
        virtual ~Mediator(){}
};
 
class Colleague
{
protected:
        Mediator *mediator;
public:
        Colleague(Mediator *mediator)
        {
                this->mediator=mediator;
        }
        virtual ~Colleague(){}
};
 
class ConcreteColleague1:public Colleague
{
public:
        ConcreteColleague1(Mediator *mediator):Colleague(mediator)
        {
        }
 
        void Send(std::string message)
        {
                mediator->Send(message, this);
        }
 
        void Notify(std::string message)
        {
                std::cout << "Colleague1 gets message " << message.c_str() << std::endl;
        }
};
 
class ConcreteColleague2:public Colleague
{
public:
        ConcreteColleague2(Mediator *mediator):Colleague(mediator)
        {
        }
 
        void Send(std::string message)
        {
                mediator->Send(message, this);
        }
 
        void Notify(std::string message)
        {
                std::cout << "Colleague2 gets message " << message.c_str() << std::endl;
        }
};
 
class ConcreteMediator:public Mediator
{
protected:
        ConcreteColleague1      *m_Colleague1;
        ConcreteColleague2      *m_Colleague2;
public:
        void SetColleague1(ConcreteColleague1 *c)
        {
                m_Colleague1=c;
        }
 
        void SetColleague2(ConcreteColleague2 *c)
        {
                m_Colleague2=c;
        }
 
        virtual void Send(std::string message, Colleague *colleague)
        {
                if (colleague==static_cast<Colleague*>(m_Colleague1))
                {
                        m_Colleague2->Notify(message);
                }
                else if (colleague==static_cast<Colleague*>(m_Colleague2))
                {
                        m_Colleague1->Notify(message);
                }
        }
};
 
int main(int argc, char **argv)
{
        ConcreteMediator *m = new ConcreteMediator();
 
        ConcreteColleague1 *c1 = new ConcreteColleague1(m);
        ConcreteColleague2 *c2 = new ConcreteColleague2(m);
 
        m->SetColleague1(c1);
        m->SetColleague2(c2);
 
        c1->Send("How are you?");
        c2->Send("Fine, thanks");
 
        std::cin.get();
        return 0;
}
 
Output
Colleague2 gеts message How are you?
Colleague1 gеts message Fine, thanks

Источники

Ссылки

• Паттерн Chain of Responsibility (цепочка обязанностей) — назначение, описание, особенности и реализация на С++.