composer.json中的自動加載部分是什麼？

Composer.json的autoload配置用於自動加載PHP類，避免手動包含文件。使用PSR-4標準可將命名空間映射到目錄，如"App\": "src/"表示App命名空間下的類位於src/目錄中；classmap用於掃描特定目錄生成類映射，適用於無命名空間的遺留代碼；files用於每次加載指定文件，適合函數或常量定義文件；修改配置後需運行composer dump-autoload生成自動加載器，生產環境可用--optimize或--classmap-authoritative優化性能。

The autoload section in composer.json is where you define how your project's PHP classes should be automatically loaded. Instead of manually including every file with require or include , Composer uses this configuration to generate an autoloader that maps class names to file paths.

This makes it easier to manage dependencies and keep your code organized, especially as your project grows.

Using PSR-4 Autoloading

PSR-4 is the most commonly used standard for autoloading in modern PHP projects. It defines a way to map namespaces to directories, so Composer knows where to find each class based on its namespace.

In your composer.json , it might look like this:

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

This means any class in the App namespace will be found under the src/ directory. For example:

• App\Controllers\HomeController → src/Controllers/HomeController.php
• App\Models\User → src/Models/User.php

After updating this, you need to run composer dump-autoload to regenerate the autoloader files.

Classmap and Files Autoloading

Sometimes not all code follows PSR-4 standards — legacy code or procedural libraries might not use namespaces at all. That's where other autoload options come in handy.

Classmap scans specific directories and builds a map of class names to files:

 {
  "autoload": {
    "classmap": ["legacy-code/", "database/seeds/"]
  }
}

Files loads specific files every time, useful for functions or constants:

 {
  "autoload": {
    "files": ["helpers.php", "config.php"]
  }
}

These are helpful when you can't control how the code is structured but still want autoloading behavior.

Optimizing and Dumping Autoload

Once you've configured your autoload settings, running composer dump-autoload (or composer dump ) generates the actual autoloader files.

Some tips:

• Always run dump-autoload after editing composer.json
• Use --optimize or -o flag in production to speed up loading by writing out all classes into one map
• You can also use --classmap-authoritative if you want Composer to only use the classmap and skip runtime checks (good for performance)

That's basically how the autoload section works in composer.json . It's straightforward once you understand the mapping logic, but easy to mess up if you forget to update the autoloader after moving files around.

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