The Adapter Design Pattern is a structural pattern that allows objects with incompatible interfaces to work together. It acts as an intermediary (or adapter) between two objects, converting the interface of one object to the interface expected by the other. This allows classes that would otherwise be incompatible because they have different interfaces to cooperate without modifications to their original code.
Adapter Structure
The Adapter pattern is generally composed of three main elements:
-
Client
: The class that expects to work with objects of a specific interface. -
Adaptee
: The class that has an interface that is incompatible with the client, but whose functionalities are necessary. -
Adapter
: The class that implements the interface expected by the client and converts calls to theAdaptee
interface.
Types of Adapters
- Object Adapter: Composition-based. The Adapter contains an instance of the class it is adapting.
- Class Adapter: Inheritance-based (usually in languages that support multiple inheritance).
When to use the Adapter?
- When you want to use an existing class, but its interface does not match what the client expects.
- To integrate new functionality into a legacy system, without having to modify the old code.
This pattern is useful in systems that need to work with external libraries or APIs, allowing you to adapt their functionality without changing the code of these libraries.
Example Using PHPMailer
Here is an example of how to use the Adapter Design Pattern to integrate PHPMailer with a custom interface.
Situation:
Let's assume that your system expects any email sending class to implement an interface called IMailer
, but PHPMailer does not follow this interface directly. The Adapter will be used to adapt PHPMailer to the interface expected by the system.
Install PHPMailer via Composer
composer require phpmailer/phpmailer
Directory System
📦Adapter
┣ 📂src
┃ ┣ 📂Interfaces
┃ ┃ ┗ 📜IMailer.php
┃ ┣ 📂Adapters
┃ ┃ ┗ 📜PHPMailerAdapter.php
┃ ┗ 📂Services
┃ ┗ 📜ServicoDeEmail.php
┣ 📂vendor
┣ 📜composer.json
┗ 📜index.php
Autoload
In the composer.json
file (located at the root of the project), add the App
namespace to automatically load the classes:
{
"autoload": {
"psr-4": {
"App\\": "src/"
}
},
"require": {
"phpmailer/phpmailer": "^6.5"
}
}
Interface IMailer
namespace App\Interfaces;
interface IMailer {
public function send($to, $subject, $message);
}
Class PHPMailerAdapter
namespace App\Adapters;
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;
use App\Interfaces\IMailer;
class PHPMailerAdapter implements IMailer {
private $phpMailer;
public function __construct() {
$this->phpMailer = new PHPMailer(true);
// Basic PHPMailer configuration
$this->phpMailer->isSMTP();
$this->phpMailer->Host = 'smtp.example.com';
$this->phpMailer->SMTPAuth = true;
$this->phpMailer->Username = 'your-email@example.com';
$this->phpMailer->Password = 'password';
$this->phpMailer->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
$this->phpMailer->Port = 587;
$this->phpMailer->setFrom('your-email@example.com', 'Your Name');
}
}
- Method send
public function send($to, $subject, $message) {
try {
$this->phpMailer->addAddress($to);
$this->phpMailer->Subject = $subject;
$this->phpMailer->Body = $message;
$this->phpMailer->send();
echo 'Email sent successfully!';
} catch (Exception $e) {
echo "Failed to send email: {$this->phpMailer->ErrorInfo}";
}
}
Class EmailService
namespace App\Services;
use App\Interfaces\IMailer;
class EmailService {
private $mailer;
public function __construct(IMailer $mailer) {
$this->mailer = $mailer;
}
}
- Method sendEmailToClient
public function sendEmailToClient($to, $subject, $message) {
$this->mailer->send($to, $subject, $message);
}
File index.php
require 'vendor/autoload.php';
use App\Adapters\PHPMailerAdapter;
use App\Services\EmailService;
// Creating the PHPMailer Adapter
$mailer = new PHPMailerAdapter();
// Using the email service with the IMailer interface
$emailService = new EmailService($mailer);
// Sending an email
$emailService->sendEmailToClient('client@example.com', 'Email Subject', 'Message content.');
Explanation of the Structure
-
IMailer.php
: Defines the IMailer interface that any email system should implement. -
PHPMailerAdapter.php
: Adapts PHPMailer to the IMailer interface. -
EmailService.php
: Email service that uses the IMailer interface to send emails. -
index.php
: Main file that uses the email service to send a message.
Top comments (2)
Interesting post! Could you explain the key differences between an Object Adapter and a Class Adapter in a bit more detail? I'd love to know when you'd choose one over the other.
The difference between Class Adapter and Object Adapter is in the way adaptation is implemented to allow communication between two incompatible interfaces. Both types follow the same general principle, but differ in their structure and usage.
Class Adapter
The Class Adapter is implemented using inheritance. It adapts an incompatible interface to another by inheriting from both classes (or a class and an interface) and redefining or modifying the necessary methods. This is only possible in languages that support multiple inheritance.
Features:
Class Adapter Example
Imagine we have a class
OldLogger
with alogMessage()
method, but we want to adapt it to aLoggerInterface
interface that requires thelog()
method.In a language with multiple inheritance, the Class Adapter could be implemented like this:
Here,
LoggerAdapter
inherits fromOldLogger
and implementsLoggerInterface
, adapting thelog()
method to calllogMessage()
.Object Adapter
The Object Adapter is implemented using composition instead of inheritance. Instead of inheriting from the class that needs to be adapted, it contains an instance of that class and delegates method calls to it. This provides more flexibility and is a more common solution because it avoids the problems of multiple inheritance.
Features:
Object Adapter Example
Let's adapt the same
OldLogger
toLoggerInterface
, but now using the Object Adapter:Here,
LoggerAdapter
does not inherit fromOldLogger
; instead, it holds an instance ofOldLogger
and callslogMessage()
through it. This allows you to swap out the internalOldLogger
instance easily if needed.In PHP, it is not possible to implement a Class Adapter , as PHP does not support multiple inheritance.
Summary
In general, Object Adapters are preferred because they offer greater flexibility and avoid the pitfalls of multiple inheritance.