自动加载 PSR-0
使用一个通用的自动加载器(autoloader)，你所需要遵守的规范：
规范
一个完全标准的
命名空间(namespace)和类(class)的结构是这样的：\<Vendor Name>\(<Namespace>\)*<Class Name>每个
命名空间(namespace)都必须有一个顶级的空间名(namespace)("组织名(Vendor Name)")。每个
命名空间(namespace)中可以根据需要使用任意数量的子命名空间(sub-namespace)。从文件系统中加载源文件时，
空间名(namespace)中的分隔符将被转换为DIRECTORY_SEPARATOR。类名(class name)中的每个下划线_都将被转换为一个DIRECTORY_SEPARATOR。下划线_在空间名(namespace)中没有什么特殊的意义。完全标准的
命名空间(namespace)和类(class)从文件系统加载源文件时将会加上.php后缀。组织名(vendor name)，空间名(namespace)，类名(class name)都由大小写字母组合而成。
示例
\Doctrine\Common\IsolatedClassLoader => /path/to/project/lib/vendor/Doctrine/Common/IsolatedClassLoader.php \Symfony\Core\Request => /path/to/project/lib/vendor/Symfony/Core/Request.php \Zend\Acl => /path/to/project/lib/vendor/Zend/Acl.php \Zend\Mail\Message => /path/to/project/lib/vendor/Zend/Mail/Message.php
空间名(namespace)和类名(class name)中的下划线
\namespace\package\Class_Name => /path/to/project/lib/vendor/namespace/package/Class/Name.php \namespace\package_name\Class_Name => /path/to/project/lib/vendor/namespace/package_name/Class/Name.php
以上是我们为实现通用的自动加载而制定的最低标准。你可以利用能够自动加载PHP 5.3类的SplClassLoader来测试你的代码是否符合这些标准。
实例
下面是一个怎样利用上述标准来实现自动加载的示例函数。
<?php
function autoload($className){
$className = ltrim($className, '\\');
$fileName = '';
$namespace = '';
if ($lastNsPos = strrpos($className, '\\')) {
$namespace = substr($className, 0, $lastNsPos);
$className = substr($className, $lastNsPos + 1);
$fileName = str_replace('\\', DIRECTORY_SEPARATOR, $namespace) . DIRECTORY_SEPARATOR;
}
$fileName .= str_replace('_', DIRECTORY_SEPARATOR, $className) . '.php';
require $fileName;
}SplClassLoader实现
下面的gist是一个按照上面建议的标准来自动加载类的SplClassLoader实例。这是依据这些标准来加载PHP 5.3类的推荐方案。
<?php
/*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* This software consists of voluntary contributions made by many individuals
* and is licensed under the MIT license. For more information, see
* <http://www.doctrine-project.org>.
*/
/**
* SplClassLoader implementation that implements the technical interoperability
* standards for PHP 5.3 namespaces and class names.
*
* http://groups.google.com/group/php-standards/web/psr-0-final-proposal?pli=1
*
* // Example which loads classes for the Doctrine Common package in the
* // Doctrine\Common namespace.
* $classLoader = new SplClassLoader('Doctrine\Common', '/path/to/doctrine');
* $classLoader->register();
*
* @license http://www.opensource.org/licenses/mit-license.html MIT License
* @author Jonathan H. Wage <jonwage@gmail.com>
* @author Roman S. Borschel <roman@code-factory.org>
* @author Matthew Weier O'Phinney <matthew@zend.com>
* @author Kris Wallsmith <kris.wallsmith@gmail.com>
* @author Fabien Potencier <fabien.potencier@symfony-project.org>
*/
class SplClassLoader
{
private $_fileExtension = '.php';
private $_namespace;
private $_includePath;
private $_namespaceSeparator = '\\';
/**
* Creates a new <tt>SplClassLoader</tt> that loads classes of the
* specified namespace.
*
* @param string $ns The namespace to use.
*/
public function __construct($ns = null, $includePath = null)
{
$this->_namespace = $ns;
$this->_includePath = $includePath;
}
/**
* Sets the namespace separator used by classes in the namespace of this class loader.
*
* @param string $sep The separator to use.
*/
public function setNamespaceSeparator($sep)
{
$this->_namespaceSeparator = $sep;
}
/**
* Gets the namespace seperator used by classes in the namespace of this class loader.
*
* @return void
*/
public function getNamespaceSeparator()
{
return $this->_namespaceSeparator;
}
/**
* Sets the base include path for all class files in the namespace of this class loader.
*
* @param string $includePath
*/
public function setIncludePath($includePath)
{
$this->_includePath = $includePath;
}
/**
* Gets the base include path for all class files in the namespace of this class loader.
*
* @return string $includePath
*/
public function getIncludePath()
{
return $this->_includePath;
}
/**
* Sets the file extension of class files in the namespace of this class loader.
*
* @param string $fileExtension
*/
public function setFileExtension($fileExtension)
{
$this->_fileExtension = $fileExtension;
}
/**
* Gets the file extension of class files in the namespace of this class loader.
*
* @return string $fileExtension
*/
public function getFileExtension()
{
return $this->_fileExtension;
}
/**
* Installs this class loader on the SPL autoload stack.
*/
public function register()
{
spl_autoload_register(array($this, 'loadClass'));
}
/**
* Uninstalls this class loader from the SPL autoloader stack.
*/
public function unregister()
{
spl_autoload_unregister(array($this, 'loadClass'));
}
/**
* Loads the given class or interface.
*
* @param string $className The name of the class to load.
* @return void
*/
public function loadClass($className)
{
if (null === $this->_namespace || $this->_namespace.$this->_namespaceSeparator === substr($className, 0, strlen($this->_namespace.$this->_namespaceSeparator))) {
$fileName = '';
$namespace = '';
if (false !== ($lastNsPos = strripos($className, $this->_namespaceSeparator))) {
$namespace = substr($className, 0, $lastNsPos);
$className = substr($className, $lastNsPos + 1);
$fileName = str_replace($this->_namespaceSeparator, DIRECTORY_SEPARATOR, $namespace) . DIRECTORY_SEPARATOR;
}
$fileName .= str_replace('_', DIRECTORY_SEPARATOR, $className) . $this->_fileExtension;
require ($this->_includePath !== null ? $this->_includePath . DIRECTORY_SEPARATOR : '') . $fileName;
}
}
} 
