一直在用 composer，最近想看一下具体的原理是什么，就仔细阅读了一下源码，一下是个人理解。在看该文章前最好了解一下 PSR-4 自动加载规范
引入类自动加载文件
# 加载类自动加载文件
require __DIR__.'/../vendor/autoload.php';
# autoload.php 入口文件
require_once __DIR__ . '/composer/autoload_real.php';
return ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c::getLoader();
composer 目录文件
根目录 composer/
- autoload_namespaces.php 为需要加载的命名空间前缀定义路径
- autoload_classmap.php 为所有需要自动加载的类定义路径
- autoload_files.php 定义所有需要加载的配置文件
- autoload_psr4.php 根据 Psr4 规范定义命名空间前缀和路径
- autoload_static.php 包含所有需要加载的文件、类，内容包含以上文件
- autoload_real.php 自动加载配置
- ClassLoader.php 自动加载类
autoload_real.php 解析
<?php
// autoload_real.php @generated by Composer
class ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c
{
private static $loader;
public static function loadClassLoader($class)
{
// 调用自动加载类 ClassLoader.php
if ('ComposerAutoloadClassLoader' === $class) {
require __DIR__ . '/ClassLoader.php';
}
}
// 实例化 ClassLoader 类，并注册所有需要加载文件的地址
public static function getLoader()
{
if (null !== self::$loader) {
return self::$loader;
}
// 将 loadClassLoader 注册为 __autoload 函数
spl_autoload_register(array('ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c', 'loadClassLoader'), true, true);
// 实例化自动加载类
self::$loader = $loader = new ComposerAutoloadClassLoader();
// 注销 __autoload 函数
spl_autoload_unregister(array('ComposerAutoloaderInit8ff9bdcc605ff8ad74a329b1634c155c', 'loadClassLoader'));
// 判断 PHP 版本 以及 HHVM_VERSION
$useStaticLoader = PHP_VERSION_ID >= 50600 && !defined('HHVM_VERSION') && (!function_exists('zend_loader_file_encoded') || !zend_loader_file_encoded());
if ($useStaticLoader) {
// autoload_static.php 为所有需要加载的文件
require_once __DIR__ . '/autoload_static.php';
// 初始化需要加载的数据，调用通过 autoload_static.php 中定义的值
call_user_func(ComposerAutoloadComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::getInitializer($loader));
} else {
// 加载的已定义命名空间
$map = require __DIR__ . '/autoload_namespaces.php';
foreach ($map as $namespace => $path) {
$loader->set($namespace, $path);
}
// 加载已定义的命名空间前缀和路径
$map = require __DIR__ . '/autoload_psr4.php';
foreach ($map as $namespace => $path) {
$loader->setPsr4($namespace, $path);
}
// 加载已定义的所有类
$classMap = require __DIR__ . '/autoload_classmap.php';
if ($classMap) {
$loader->addClassMap($classMap);
}
}
// 注册自动加载方法 __atuoload()
$loader->register(true);
if ($useStaticLoader) {
// 加载基础配置文件
$includeFiles = ComposerAutoloadComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$files;
} else {
$includeFiles = require __DIR__ . '/autoload_files.php';
}
foreach ($includeFiles as $fileIdentifier => $file) {
composerRequire8ff9bdcc605ff8ad74a329b1634c155c($fileIdentifier, $file);
}
return $loader;
}
}
function composerRequire8ff9bdcc605ff8ad74a329b1634c155c($fileIdentifier, $file)
{
if (empty($GLOBALS['__composer_autoload_files'][$fileIdentifier])) {
// 调用配置文件
require $file;
$GLOBALS['__composer_autoload_files'][$fileIdentifier] = true;
}
}
autoload_static.php 解析
<?php
// autoload_static.php @generated by Composer
namespace ComposerAutoload;
class ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c
{
// 基础文件
public static $files = array (
'0e6d7bf4a5811bfa5cf40c5ccd6fae6a' => __DIR__ . '/..' . '/custom/sub-custom/custom.php',
);
// 命名空间前缀及长度
public static $prefixLengthsPsr4 = array (
'p' =>
array (
'custom\sub-custom\' => 18,
),
);
// 命名空间前缀及路径
public static $prefixDirsPsr4 = array (
'sustom\sub-custom\' =>
array (
0 => __DIR__ . '/..' . '/custom/sub-custom/custom',
),
);
// 命名空间前缀及路径
public static $prefixesPsr0 = array (
'C' =>
array (
'Custom\' =>
array (
0 => __DIR__ . '/..' . '/custom/sub-custom/custom',
),
),
）
// 所有需要自动加载的类
public static $classMap = array (
'Custom\CustomController' => __DIR__ . '/../..' . 'Custom/CustomController.php',
)
public static function getInitializer(ClassLoader $loader)
{
return Closure::bind(function () use ($loader) {
$loader->prefixLengthsPsr4 = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$prefixLengthsPsr4;
$loader->prefixDirsPsr4 = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$prefixDirsPsr4;
$loader->prefixesPsr0 = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$prefixesPsr0;
// 以上为 PHP 自动加载规范
// 以下为需要加载的类
$loader->classMap = ComposerStaticInit8ff9bdcc605ff8ad74a329b1634c155c::$classMap;
}, null, ClassLoader::class);
}
ClassLoader.php 解析
<?php
/*
* This file is part of Composer.
*
* (c) Nils Adermann <naderman@naderman.de>
* Jordi Boggiano <j.boggiano@seld.be>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace ComposerAutoload;
/**
* ClassLoader implements a PSR-0, PSR-4 and classmap class loader.
*
* $loader = new ComposerAutoloadClassLoader();
*
* // register classes with namespaces
* $loader->add('SymfonyComponent', __DIR__.'/component');
* $loader->add('Symfony', __DIR__.'/framework');
*
* // activate the autoloader
* $loader->register();
*
* // to enable searching the include path (eg. for PEAR packages)
* $loader->setUseIncludePath(true);
*
* In this example, if you try to use a class in the SymfonyComponent
* namespace or one of its children (SymfonyComponentConsole for instance),
* the autoloader will first look for the class under the component/
* directory, and it will then fallback to the framework/ directory if not
* found before giving up.
*
* This class is loosely based on the Symfony UniversalClassLoader.
*
* @author Fabien Potencier <fabien@symfony.com>
* @author Jordi Boggiano <j.boggiano@seld.be>
* @see http://www.php-fig.org/psr/psr-0/
* @see http://www.php-fig.org/psr/psr-4/
*/
class ClassLoader
{
// PSR-4
private $prefixLengthsPsr4 = array();
private $prefixDirsPsr4 = array();
private $fallbackDirsPsr4 = array();
// PSR-0
private $prefixesPsr0 = array();
private $fallbackDirsPsr0 = array();
private $useIncludePath = false;
private $classMap = array();
private $classMapAuthoritative = false;
private $missingClasses = array();
private $apcuPrefix;
public function getPrefixes()
{
if (!empty($this->prefixesPsr0)) {
return call_user_func_array('array_merge', $this->prefixesPsr0);
}
return array();
}
public function getPrefixesPsr4()
{
return $this->prefixDirsPsr4;
}
public function getFallbackDirs()
{
return $this->fallbackDirsPsr0;
}
public function getFallbackDirsPsr4()
{
return $this->fallbackDirsPsr4;
}
public function getClassMap()
{
return $this->classMap;
}
/**
* @param array $classMap Class to filename map
*/
public function addClassMap(array $classMap)
{
if ($this->classMap) {
$this->classMap = array_merge($this->classMap, $classMap);
} else {
$this->classMap = $classMap;
}
}
/**
* Registers a set of PSR-0 directories for a given prefix, either
* appending or prepending to the ones previously set for this prefix.
*
* @param string $prefix The prefix
* @param array|string $paths The PSR-0 root directories
* @param bool $prepend Whether to prepend the directories
*/
public function add($prefix, $paths, $prepend = false)
{
if (!$prefix) {
if ($prepend) {
$this->fallbackDirsPsr0 = array_merge(
(array) $paths,
$this->fallbackDirsPsr0
);
} else {
$this->fallbackDirsPsr0 = array_merge(
$this->fallbackDirsPsr0,
(array) $paths
);
}
return;
}
$first = $prefix[0];
if (!isset($this->prefixesPsr0[$first][$prefix])) {
$this->prefixesPsr0[$first][$prefix] = (array) $paths;
return;
}
if ($prepend) {
$this->prefixesPsr0[$first][$prefix] = array_merge(
(array) $paths,
$this->prefixesPsr0[$first][$prefix]
);
} else {
$this->prefixesPsr0[$first][$prefix] = array_merge(
$this->prefixesPsr0[$first][$prefix],
(array) $paths
);
}
}
/**
* Registers a set of PSR-4 directories for a given namespace, either
* appending or prepending to the ones previously set for this namespace.
*
* @param string $prefix The prefix/namespace, with trailing '\'
* @param array|string $paths The PSR-4 base directories
* @param bool $prepend Whether to prepend the directories
*
* @throws InvalidArgumentException
*/
public function addPsr4($prefix, $paths, $prepend = false)
{
if (!$prefix) {
// Register directories for the root namespace.
if ($prepend) {
$this->fallbackDirsPsr4 = array_merge(
(array) $paths,
$this->fallbackDirsPsr4
);
} else {
$this->fallbackDirsPsr4 = array_merge(
$this->fallbackDirsPsr4,
(array) $paths
);
}
} elseif (!isset($this->prefixDirsPsr4[$prefix])) {
// Register directories for a new namespace.
$length = strlen($prefix);
if ('\' !== $prefix[$length - 1]) {
throw new InvalidArgumentException("A non-empty PSR-4 prefix must end with a namespace separator.");
}
$this->prefixLengthsPsr4[$prefix[0]][$prefix] = $length;
$this->prefixDirsPsr4[$prefix] = (array) $paths;
} elseif ($prepend) {
// Prepend directories for an already registered namespace.
$this->prefixDirsPsr4[$prefix] = array_merge(
(array) $paths,
$this->prefixDirsPsr4[$prefix]
);
} else {
// Append directories for an already registered namespace.
$this->prefixDirsPsr4[$prefix] = array_merge(
$this->prefixDirsPsr4[$prefix],
(array) $paths
);
}
}
/**
* Registers a set of PSR-0 directories for a given prefix,
* replacing any others previously set for this prefix.
*
* @param string $prefix The prefix
* @param array|string $paths The PSR-0 base directories
*/
public function set($prefix, $paths)
{
if (!$prefix) {
$this->fallbackDirsPsr0 = (array) $paths;
} else {
$this->prefixesPsr0[$prefix[0]][$prefix] = (array) $paths;
}
}
/**
* Registers a set of PSR-4 directories for a given namespace,
* replacing any others previously set for this namespace.
*
* @param string $prefix The prefix/namespace, with trailing '\'
* @param array|string $paths The PSR-4 base directories
*
* @throws InvalidArgumentException
*/
public function setPsr4($prefix, $paths)
{
if (!$prefix) {
$this->fallbackDirsPsr4 = (array) $paths;
} else {
$length = strlen($prefix);
if ('\' !== $prefix[$length - 1]) {
throw new InvalidArgumentException("A non-empty PSR-4 prefix must end with a namespace separator.");
}
$this->prefixLengthsPsr4[$prefix[0]][$prefix] = $length;
$this->prefixDirsPsr4[$prefix] = (array) $paths;
}
}
/**
* Turns on searching the include path for class files.
*
* @param bool $useIncludePath
*/
public function setUseIncludePath($useIncludePath)
{
$this->useIncludePath = $useIncludePath;
}
/**
* Can be used to check if the autoloader uses the include path to check
* for classes.
*
* @return bool
*/
public function getUseIncludePath()
{
return $this->useIncludePath;
}
/**
* Turns off searching the prefix and fallback directories for classes
* that have not been registered with the class map.
*
* @param bool $classMapAuthoritative
*/
public function setClassMapAuthoritative($classMapAuthoritative)
{
$this->classMapAuthoritative = $classMapAuthoritative;
}
/**
* Should class lookup fail if not found in the current class map?
*
* @return bool
*/
public function isClassMapAuthoritative()
{
return $this->classMapAuthoritative;
}
/**
* APCu prefix to use to cache found/not-found classes, if the extension is enabled.
*
* @param string|null $apcuPrefix
*/
public function setApcuPrefix($apcuPrefix)
{
$this->apcuPrefix = function_exists('apcu_fetch') && ini_get('apc.enabled') ? $apcuPrefix : null;
}
/**
* The APCu prefix in use, or null if APCu caching is not enabled.
*
* @return string|null
*/
public function getApcuPrefix()
{
return $this->apcuPrefix;
}
/**
* Registers this instance as an autoloader.
*
* @param bool $prepend Whether to prepend the autoloader or not
*/
public function register($prepend = false)
{
spl_autoload_register(array($this, 'loadClass'), true, $prepend);
}
/**
* Unregisters this instance as an autoloader.
*/
public function unregister()
{
spl_autoload_unregister(array($this, 'loadClass'));
}
/**
* Loads the given class or interface.
*
* @param string $class The name of the class
* @return bool|null True if loaded, null otherwise
*/
public function loadClass($class)
{
if ($file = $this->findFile($class)) {
includeFile($file);
return true;
}
}
/**
* Finds the path to the file where the class is defined.
*
* @param string $class The name of the class
*
* @return string|false The path if found, false otherwise
*/
public function findFile($class)
{
// class map lookup
// 如果存在直接返回
if (isset($this->classMap[$class])) {
return $this->classMap[$class];
}
if ($this->classMapAuthoritative || isset($this->missingClasses[$class])) {
return false;
}
if (null !== $this->apcuPrefix) {
$file = apcu_fetch($this->apcuPrefix.$class, $hit);
if ($hit) {
return $file;
}
}
// 没有在 classMap中找到，重新查找
$file = $this->findFileWithExtension($class, '.php');
// Search for Hack files if we are running on HHVM
if (false === $file && defined('HHVM_VERSION')) {
$file = $this->findFileWithExtension($class, '.hh');
}
if (null !== $this->apcuPrefix) {
apcu_add($this->apcuPrefix.$class, $file);
}
if (false === $file) {
// Remember that this class does not exist.
$this->missingClasses[$class] = true;
}
return $file;
}
private function findFileWithExtension($class, $ext)
{
// PSR-4 lookup
$logicalPathPsr4 = strtr($class, '\', DIRECTORY_SEPARATOR) . $ext;
$first = $class[0];
if (isset($this->prefixLengthsPsr4[$first])) {
$subPath = $class;
while (false !== $lastPos = strrpos($subPath, '\')) {
$subPath = substr($subPath, 0, $lastPos);
$search = $subPath.'\';
if (isset($this->prefixDirsPsr4[$search])) {
foreach ($this->prefixDirsPsr4[$search] as $dir) {
$length = $this->prefixLengthsPsr4[$first][$search];
if (file_exists($file = $dir . DIRECTORY_SEPARATOR . substr($logicalPathPsr4, $length))) {
return $file;
}
}
}
}
}
// PSR-4 fallback dirs
foreach ($this->fallbackDirsPsr4 as $dir) {
if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr4)) {
return $file;
}
}
// PSR-0 lookup
if (false !== $pos = strrpos($class, '\')) {
// namespaced class name
$logicalPathPsr0 = substr($logicalPathPsr4, 0, $pos + 1)
. strtr(substr($logicalPathPsr4, $pos + 1), '_', DIRECTORY_SEPARATOR);
} else {
// PEAR-like class name
$logicalPathPsr0 = strtr($class, '_', DIRECTORY_SEPARATOR) . $ext;
}
if (isset($this->prefixesPsr0[$first])) {
foreach ($this->prefixesPsr0[$first] as $prefix => $dirs) {
if (0 === strpos($class, $prefix)) {
foreach ($dirs as $dir) {
if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr0)) {
return $file;
}
}
}
}
}
// PSR-0 fallback dirs
foreach ($this->fallbackDirsPsr0 as $dir) {
if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr0)) {
return $file;
}
}
// PSR-0 include paths.
if ($this->useIncludePath && $file = stream_resolve_include_path($logicalPathPsr0)) {
return $file;
}
return false;
}
}
/**
* Scope isolated include.
*
* Prevents access to $this/self from included files.
*/
function includeFile($file)
{
include $file;
}