PSR
是制定的PHP規範，簡稱PSR，是PHP開發的事實標準。
PSR-4使代碼更加規範，能夠滿足面向package的自動載入，它規範了如何從檔案路逕自動載入類，同時規範了自動載入檔案的位置。
基本介紹
- 中文名：PSR-4
- 外文名：PSR-4
PSR介紹,代碼樣例,
PSR介紹
PSR原本有四個規範，分別是：
- PSR-0 自動載入
- PSR-1 基本代碼規範
- PSR-2 代碼樣式
- PSR-3 日誌接口
2013年底，新出了第5個規範——PSR-4。
PSR-4規範了如何指定檔案路徑從而自動載入類定義，同時規範了自動載入檔案的位置。這個乍一看和PSR-0重複了，實際上，在功能上確實有所重複。區別在於PSR-4的規範比較乾淨，去除了兼容PHP 5.3以前版本的內容，有一點PSR-0升級版的感覺。當然，PSR-4也不是要完全替代PSR-0，而是在必要的時候補充PSR-0——當然，如果你願意，PSR-4也可以替代PSR-0。PSR-4可以和包括PSR-0在內的其他自動載入機制共同使用。
PSR-4和PSR-0最大的區別是對下劃線（underscore)的定義不同。PSR-4中，在類名中使用下劃線沒有任何特殊含義。而PSR-0則規定類名中的下劃線_會被轉化成目錄分隔設定。
代碼樣例
以下代碼展示了遵循PSR-4的類定義，這個類處理多個命名空間：
<?phpnamespace Example;/** * An example of a general-purpose implementation that includes the optional * functionality of allowing multiple base directories for a single namespace * prefix. * * Given a foo-bar package of classes in the file system at the following * paths ... * * /path/to/packages/foo-bar/ * src/ * Baz.php # Foo\Bar\Baz * Qux/ * Quux.php # Foo\Bar\Qux\Quux * tests/ * BazTest.php # Foo\Bar\BazTest * Qux/ * QuuxTest.php # Foo\Bar\Qux\QuuxTest * * ... add the path to the class files for the \Foo\Bar\ namespace prefix * as follows: * * <?php * // instantiate the loader * $loader = new \Example\Psr4AutoloaderClass; * * // register the autoloader * $loader->register(); * * // register the base directories for the namespace prefix * $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/src'); * $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/tests'); * * The following line would cause the autoloader to attempt to load the * \Foo\Bar\Qux\Quux class from /path/to/packages/foo-bar/src/Qux/Quux.php: * * <?php * new \Foo\Bar\Qux\Quux; * * The following line would cause the autoloader to attempt to load the * \Foo\Bar\Qux\QuuxTest class from /path/to/packages/foo-bar/tests/Qux/QuuxTest.php: * * <?php * new \Foo\Bar\Qux\QuuxTest; */class Psr4AutoloaderClass{ /** * An associative array where the key is a namespace prefix and the value * is an array of base directories for classes in that namespace. * * @var array */ protected $prefixes = array(); /** * Register loader with SPL autoloader stack. * * @return void */ public function register() { spl_autoload_register(array($this, 'loadClass')); } /** * Adds a base directory for a namespace prefix. * * @param string $prefix The namespace prefix. * @param string $base_dir A base directory for class files in the * namespace. * @param bool $prepend If true, prepend the base directory to the stack * instead of appending it; this causes it to be searched first rather * than last. * @return void */ public function addNamespace($prefix, $base_dir, $prepend = false) { // normalize namespace prefix $prefix = trim($prefix, '\\') . '\\'; // normalize the base directory with a trailing separator $base_dir = rtrim($base_dir, '/') . DIRECTORY_SEPARATOR; $base_dir = rtrim($base_dir, DIRECTORY_SEPARATOR) . '/'; // initialize the namespace prefix array if (isset($this->prefixes[$prefix]) === false) { $this->prefixes[$prefix] = array(); } // retain the base directory for the namespace prefix if ($prepend) { array_unshift($this->prefixes[$prefix], $base_dir); } else { array_push($this->prefixes[$prefix], $base_dir); } } /** * Loads the class file for a given class name. * * @param string $class The fully-qualified class name. * @return mixed The mapped file name on success, or boolean false on * failure. */ public function loadClass($class) { // the current namespace prefix $prefix = $class; // work backwards through the namespace names of the fully-qualified // class name to find a mapped file name while (false !== $pos = strrpos($prefix, '\\')) { // retain the trailing namespace separator in the prefix $prefix = substr($class, 0, $pos + 1); // the rest is the relative class name $relative_class = substr($class, $pos + 1); // try to load a mapped file for the prefix and relative class $mapped_file = $this->loadMappedFile($prefix, $relative_class); if ($mapped_file) { return $mapped_file; } // remove the trailing namespace separator for the next iteration // of strrpos() $prefix = rtrim($prefix, '\\'); } // never found a mapped file return false; } /** * Load the mapped file for a namespace prefix and relative class. * * @param string $prefix The namespace prefix. * @param string $relative_class The relative class name. * @return mixed Boolean false if no mapped file can be loaded, or the * name of the mapped file that was loaded. */ protected function loadMappedFile($prefix, $relative_class) { // are there any base directories for this namespace prefix? if (isset($this->prefixes[$prefix]) === false) { return false; } // look through base directories for this namespace prefix foreach ($this->prefixes[$prefix] as $base_dir) { // replace the namespace prefix with the base directory, // replace namespace separators with directory separators // in the relative class name, append with .php $file = $base_dir . str_replace('\\', DIRECTORY_SEPARATOR, $relative_class) . '.php'; $file = $base_dir . str_replace('\\', '/', $relative_class) . '.php'; // if the mapped file exists, require it if ($this->requireFile($file)) { // yes, we're done return $file; } } // never found it return false; } /** * If a file exists, require it from the file system. * * @param string $file The file to require. * @return bool True if the file exists, false if not. */ protected function requireFile($file) { if (file_exists($file)) { require $file; return true; } return false; }}