PHP管理依赖(dependency)关系工具 Composer的自动加载(autoload)
Composer 是PHP的一个包依赖管理工具,类似Ruby中的RubyGems或者Node中的NPM,它并非官方,但现在已经非常流行。此文并不介绍如何使用Composer,而是关注于它的a
举例来说,假设我们的项目想要使用 monolog 这个日志工具,就需要在composer.json里告诉composer我们需要它:
{ "require": { "monolog/monolog": "1.*" } }
之后执行:
php composer.phar install
好,现在安装完了,该怎么使用呢?Composer自动生成了一个autoload文件,你只需要引用它
require '/path/to/vendor/autoload.php';
然后就可以非常方便的去使用第三方的类库了,是不是感觉很棒啊!对于我们需要的monolog,就可以这样用了:
use Monolog\Logger; use Monolog\Handler\StreamHandler; // create a log channel $log = new Logger('name'); $log->pushHandler(new StreamHandler('/path/to/log/log_name.log', Logger::WARNING)); // add records to the log $log->addWarning('Foo'); $log->addError('Bar');
在这个过程中,Composer做了什么呢?它生成了一个autoloader,再根据各个包自己的autoload配置,从而帮我们进行自动加载的工作。(如果对autoload这部分内容不太了解,可以看我之前的 一篇文章
)接下来让我们看看Composer是怎么做的吧。
对于第三方包的自动加载,Composer提供了四种方式的支持,分别是 PSR-0和PSR-4的自动加载(我的一篇文章也有介绍过它们),生成class-map,和直接包含files的方式。
PSR-4是composer推荐使用的一种方式,因为它更易使用并能带来更简洁的目录结构。在composer.json里是这样进行配置的:
{ "autoload": { "psr-4": { "Foo\\": "src/", } } }
key和value就定义出了namespace以及到相应path的映射。按照PSR-4的规则,当试图自动加载 "Foo\\Bar\\Baz" 这个class时,会去寻找 "src/Bar/Baz.php" 这个文件,如果它存在则进行加载。注意, "Foo\\"
并没有出现在文件路径中,这是与PSR-0不同的一点,如果PSR-0有此配置,那么会去寻找
"src/Foo/Bar/Baz.php"
这个文件。
另外注意PSR-4和PSR-0的配置里,"Foo\\"结尾的命名空间分隔符必须加上并且进行转义,以防出现"Foo"匹配到了"FooBar"这样的意外发生。
在composer安装或更新完之后,psr-4的配置换被转换成namespace为key,dir path为value的Map的形式,并写入生成的 vendor/composer/autoload_psr4.php 文件之中。
{ "autoload": { "psr-0": { "Foo\\": "src/", } } }
最终这个配置也以Map的形式写入生成的
vendor/composer/autoload_namespaces.php
文件之中。
Class-map方式,则是通过配置指定的目录或文件,然后在Composer安装或更新时,它会扫描指定目录下以.php或.inc结尾的文件中的class,生成class到指定file path的映射,并加入新生成的 vendor/composer/autoload_classmap.php 文件中,,。
{ "autoload": { "classmap": ["src/", "lib/", "Something.php"] } }
例如src/下有一个BaseController类,那么在autoload_classmap.php文件中,就会生成这样的配置:
'BaseController' => $baseDir . '/src/BaseController.php'
Files方式,就是手动指定供直接加载的文件。比如说我们有一系列全局的helper functions,可以放到一个helper文件里然后直接进行加载
{ "autoload": { "files": ["src/MyLibrary/functions.php"] } }
它会生成一个array,包含这些配置中指定的files,再写入新生成的
vendor/composer/autoload_files.php
文件中,以供autoloader直接进行加载。
下面来看看composer autoload的代码吧
$path) { $loader->set($namespace, $path); } $map = require __DIR__ . '/autoload_psr4.php'; foreach ($map as $namespace => $path) { $loader->setPsr4($namespace, $path); } $classMap = require __DIR__ . '/autoload_classmap.php'; if ($classMap) { $loader->addClassMap($classMap); } $loader->register(true); $includeFiles = require __DIR__ . '/autoload_files.php'; foreach ($includeFiles as $file) { composerRequire73612b48e6c3d0de8d56e03dece61d11($file); } return $loader; } } function composerRequire73612b48e6c3d0de8d56e03dece61d11($file) { require $file; }
首先初始化ClassLoader类,然后依次用上面提到的4种加载方式来注册/直接加载,ClassLoader的一些核心代码如下:
/** * @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, * 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; } } /** * 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); } /** * 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) { //这是PHP5.3.0 - 5.3.2的一个bug 详见https://bugs.php.net/50731 if ('\\' == $class[0]) { $class = substr($class, 1); } // class map 方式的查找 if (isset($this->classMap[$class])) { return $this->classMap[$class]; } //psr-0/4方式的查找 $file = $this->findFileWithExtension($class, '.php'); // Search for Hack files if we are running on HHVM if ($file === null && defined('HHVM_VERSION')) { $file = $this->findFileWithExtension($class, '.hh'); } if ($file === null) { // Remember that this class does not exist. return $this->classMap[$class] = false; } return $file; } private function findFileWithExtension($class, $ext) { // PSR-4 lookup $logicalPathPsr4 = strtr($class, '\\', DIRECTORY_SEPARATOR) . $ext; $first = $class[0]; if (isset($this->prefixLengthsPsr4[$first])) { foreach ($this->prefixLengthsPsr4[$first] as $prefix => $length) { if (0 === strpos($class, $prefix)) { foreach ($this->prefixDirsPsr4[$prefix] as $dir) { if (file_exists($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; } } /** * Scope isolated include. * * Prevents access to $this/self from included files. */ function includeFile($file) { include $file; }

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