Tại sao muốn kiểm soát quyền truy cập vào một đối tượng?

Đây là một ví dụ: bạn có một đối tượng database lớn tiêu thụ một lượng lớn tài nguyên hệ thống. Bạn cần nó theo thời gian, nhưng không phải lúc nào cũng cần dùng đến.

Mẫu Proxy gợi ý rằng bạn tạo một lớp proxy mới có cùng giao diện với đối tượng dịch vụ gốc. Sau đó, bạn cập nhật ứng dụng của mình để nó chuyển đối tượng proxy cho tất cả các máy khách của đối tượng gốc. Khi nhận được yêu cầu từ máy khách, proxy tạo một đối tượng dịch vụ thực và phân công tất cả công việc cho đối tượng đó.

Trong phần mềm hệ thống proxy chủ yếu dùng để kiểm soát, bảo vệ & điều hướng dữ liệu đầu vào.

Ví dụ 1:

LeaderObject.php

<?php
 
namespace App\Utils\Object;
 
/**
 * LeaderObject
 */
class LeaderObject
{          
  /**
   * reviceRequestOffer
   *
   * @param  mixed $offer
   * @return string
   */
  public function reviceRequestOffer($offer)
  {
      return "Offer {$offer} is ok!";
  }
}

SecretaryProxy.php

<?php
 
namespace App\Utils\Proxy;
use App\Utils\Object\LeaderObject;
 
/**
 * SecretaryProxy
 */
class SecretaryProxy
{            
    /**
     * leader
     *
     * @var mixed
     */
    private $leader;    
    /**
     * __construct
     *
     * @param  mixed $leader
     * @return void
     */
    public function __construct(LeaderObject $leader) {
        $this->leader = $leader;
    }
 
    /**
     * reviceRequestOffer
     *
     * @param  mixed $offer
     * @return string
     */
    public function reviceRequestOffer($offer)
    {
        // ...
 
        return $this->leader->reviceRequestOffer($offer);
    }    
}

DeveloperObject.php

<?php
 
namespace App\Utils\Object;
use App\Utils\Proxy\SecretaryProxy;
 
/**
 * DeveloperObject
 */
class DeveloperObject
{           
   /**
    * applyFor
    *
    * @param  mixed $secretary
    * @param  mixed $offer
    * @return string
    */
   public function applyFor(SecretaryProxy $secretary, $offer)
   {
       return $secretary->reviceRequestOffer($offer);
   }
}

ProxyCommand.php

<?php
 
namespace App\Console\Commands\Test;
 
use App\Utils\Object\DeveloperObject;
use App\Utils\Object\LeaderObject;
use App\Utils\Proxy\SecretaryProxy;
use Illuminate\Console\Command;
 
/**
 * Class ProxyCommand
 * @package Modules\Web\Console\Commands
 */
class ProxyCommand extends Command
{
    /**
     * The console command name.
     *
     * @var string
     */
    protected $signature = 'test:proxy';
 
    public function handle(){
        $leader = new LeaderObject();
        $developer = new DeveloperObject();
 
        $result = $developer->applyFor(new SecretaryProxy($leader), '50M');
 
        $this->info($result);
    }
 
}

Ví dụ 2:

<?php
 
namespace RefactoringGuru\Proxy\Conceptual;
 
/**
 * The Subject interface declares common operations for both RealSubject and the
 * Proxy. As long as the client works with RealSubject using this interface,
 * you'll be able to pass it a proxy instead of a real subject.
 */
interface Subject
{
    public function request(): void;
}
 
/**
 * The RealSubject contains some core business logic. Usually, RealSubjects are
 * capable of doing some useful work which may also be very slow or sensitive -
 * e.g. correcting input data. A Proxy can solve these issues without any
 * changes to the RealSubject's code.
 */
class RealSubject implements Subject
{
    public function request(): void
    {
        echo "RealSubject: Handling request.\n";
    }
}
 
/**
 * The Proxy has an interface identical to the RealSubject.
 */
class Proxy implements Subject
{
    /**
     * @var RealSubject
     */
    private $realSubject;
 
    /**
     * The Proxy maintains a reference to an object of the RealSubject class. It
     * can be either lazy-loaded or passed to the Proxy by the client.
     */
    public function __construct(RealSubject $realSubject)
    {
        $this->realSubject = $realSubject;
    }
 
    /**
     * The most common applications of the Proxy pattern are lazy loading,
     * caching, controlling the access, logging, etc. A Proxy can perform one of
     * these things and then, depending on the result, pass the execution to the
     * same method in a linked RealSubject object.
     */
    public function request(): void
    {
        if ($this->checkAccess()) {
            $this->realSubject->request();
            $this->logAccess();
        }
    }
 
    private function checkAccess(): bool
    {
        // Some real checks should go here.
        echo "Proxy: Checking access prior to firing a real request.\n";
 
        return true;
    }
 
    private function logAccess(): void
    {
        echo "Proxy: Logging the time of request.\n";
    }
}
 
/**
 * The client code is supposed to work with all objects (both subjects and
 * proxies) via the Subject interface in order to support both real subjects and
 * proxies. In real life, however, clients mostly work with their real subjects
 * directly. In this case, to implement the pattern more easily, you can extend
 * your proxy from the real subject's class.
 */
function clientCode(Subject $subject)
{
    // ...
 
    $subject->request();
 
    // ...
}
 
echo "Client: Executing the client code with a real subject:\n";
$realSubject = new RealSubject();
clientCode($realSubject);
 
echo "\n";
 
echo "Client: Executing the same client code with a proxy:\n";
$proxy = new Proxy($realSubject);
clientCode($proxy);

Ví dụ 3:

<?php
 
namespace RefactoringGuru\Proxy\RealWorld;
 
/**
 * The Subject interface describes the interface of a real object.
 *
 * The truth is that many real apps may not have this interface clearly defined.
 * If you're in that boat, your best bet would be to extend the Proxy from one
 * of your existing application classes. If that's awkward, then extracting a
 * proper interface should be your first step.
 */
interface Downloader
{
    public function download(string $url): string;
}
 
/**
 * The Real Subject does the real job, albeit not in the most efficient way.
 * When a client tries to download the same file for the second time, our
 * downloader does just that, instead of fetching the result from cache.
 */
class SimpleDownloader implements Downloader
{
    public function download(string $url): string
    {
        echo "Downloading a file from the Internet.\n";
        $result = file_get_contents($url);
        echo "Downloaded bytes: " . strlen($result) . "\n";
 
        return $result;
    }
}
 
/**
 * The Proxy class is our attempt to make the download more efficient. It wraps
 * the real downloader object and delegates it the first download calls. The
 * result is then cached, making subsequent calls return an existing file
 * instead of downloading it again.
 *
 * Note that the Proxy MUST implement the same interface as the Real Subject.
 */
class CachingDownloader implements Downloader
{
    /**
     * @var SimpleDownloader
     */
    private $downloader;
 
    /**
     * @var string[]
     */
    private $cache = [];
 
    public function __construct(SimpleDownloader $downloader)
    {
        $this->downloader = $downloader;
    }
 
    public function download(string $url): string
    {
        if (!isset($this->cache[$url])) {
            echo "CacheProxy MISS. ";
            $result = $this->downloader->download($url);
            $this->cache[$url] = $result;
        } else {
            echo "CacheProxy HIT. Retrieving result from cache.\n";
        }
        return $this->cache[$url];
    }
}
 
/**
 * The client code may issue several similar download requests. In this case,
 * the caching proxy saves time and traffic by serving results from cache.
 *
 * The client is unaware that it works with a proxy because it works with
 * downloaders via the abstract interface.
 */
function clientCode(Downloader $subject)
{
    // ...
 
    $result = $subject->download("http://example.com/");
 
    // Duplicate download requests could be cached for a speed gain.
 
    $result = $subject->download("http://example.com/");
 
    // ...
}
 
echo "Executing client code with real subject:\n";
$realSubject = new SimpleDownloader();
clientCode($realSubject);
 
echo "\n";
 
echo "Executing the same client code with a proxy:\n";
$proxy = new CachingDownloader($realSubject);
clientCode($proxy);

• https://refactoring.guru/design-patterns/proxy
• https://www.youtube.com/watch?v=Z3mPTWuFw00