16. Composer & Packages (PHP)

🔹 What is Composer?

Composer is a dependency manager for PHP.

👉 Simple meaning:
It helps you install, manage, and update external libraries (packages) in your PHP project.

💡 Example:
Instead of writing everything from scratch, you can install ready-made libraries like:

• Payment gateways
• Email sending (PHPMailer)
• PDF generation
• APIs integration

👉 Composer does this automatically.

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🔹 Why Composer is Important?

Without Composer ❌

• Manually download files
• Handle dependencies yourself
• Difficult updates

With Composer ✅

• One command installs everything
• Automatically loads files
• Easy updates

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🔹 Installing Composer

Step 1: Download Composer

Go to:
👉 https://getcomposer.org/

Step 2: Install

For Windows:

• Download Composer-Setup.exe
• Install normally

Check installation:

composer -v

If version shows → Installed successfully ✅

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🔹 Composer Basic Commands

1. Initialize project

composer init

2. Install dependencies

composer install

3. Add a package

composer require monolog/monolog

4. Update packages

composer update

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🔹 Installing Libraries (Packages)

👉 Example: Install PHPMailer

composer require phpmailer/phpmailer

Composer will:

• Download package
• Create vendor/ folder
• Update composer.json
• Generate autoload file

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🔹 composer.json File

This is the main file for Composer.

Example:

{
  "require": {
    "phpmailer/phpmailer": "^6.0"
  }
}

👉 It stores:

• Project dependencies
• Version control

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🔹 Autoloading (Very Important)

Composer provides automatic class loading.

👉 Instead of:

require 'file1.php';
require 'file2.php';
require 'file3.php';

👉 Use:

require 'vendor/autoload.php';

Now all classes are automatically loaded ✅

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🔹 Example Usage

<?phprequire 'vendor/autoload.php';use PHPMailer\PHPMailer\PHPMailer;$mail = new PHPMailer();
$mail->setFrom('test@example.com', 'Test');
$mail->addAddress('user@example.com');
$mail->Subject = 'Hello';
$mail->Body = 'This is a test email';$mail->send();

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🔹 PSR-4 Autoloading (Advanced)

You can define your own classes:

{
  "autoload": {
    "psr-4": {
      "App\\": "src/"
    }
  }
}

Then run:

composer dump-autoload

Now you can use:

use App\Controllers\UserController;

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🔹 Folder Structure After Composer

project/
│
├── composer.json
├── composer.lock
├── vendor/
│   ├── autoload.php
│   └── packages...

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🔥 Interview Questions

• What is Composer in PHP?
• Difference between require and require_once vs Composer autoload?
• What is composer.json?
• What is PSR-4?
• Difference between install and update?