What is the autoload section in composer.json?
Jun 12, 2025 pm 12:57 PMComposer.json's autoload configuration is used to automatically load PHP classes, avoiding manual inclusion of files. Use the PSR-4 standard to map the namespace to a directory, such as "App\": "src/" means that the class under the App namespace is located in the src/ directory; classmap is used to scan specific directories to generate class maps, suitable for legacy code without namespace; files are used to load a specified file each time, suitable for function or constant definition files; after modifying the configuration, you need to run composer dump-autoload to generate an automatic loader, and the production environment can use --optimize or --classmap-authoritative optimization performance.
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 editingcomposer.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.
The above is the detailed content of What is the autoload section in composer.json?. For more information, please follow other related articles on the PHP Chinese website!

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