以下是 PSR-4 规范的相关示例代码：
<?php
/**
* 一个具体项目的实例
*
* 当使用 SPL 注册此自动加载器后，执行以下语句将从
* /path/to/project/src/Baz/Qux.php 载入 \Foo\Bar\Baz\Qux 类：
*
* new \Foo\Bar\Baz\Qux;
*
* @param string $class 完整的类名
* @return void
*/
spl_autoload_register(function ($class) {
// 具体项目命名空间前缀
$prefix = 'Foo\\Bar\\';
// 命名空间前缀的基目录
$base_dir = __DIR__ . '/src/';
// 判断类名是否具有本命名空间前缀
$len = strlen($prefix);
if (strncmp($prefix, $class, $len) !== 0) {
// 不含本命名空间前缀，退出本自动载入器
return;
}
// 截取相应类名
$relative_class = substr($class, $len);
// 将命名空间前缀替作为文件基目录，然后
// 将类名中的命名空间分隔符替换成文件分隔符,
// 最后添加 .php 后缀
$file = $base_dir . str_replace('\\', '/', $relative_class) . '.php';
// 如果以上文件存在，则将其载入
if (file_exists($file)) {
require $file;
}
});下面是一个可处理多命名空间的类实例
<?php
namespace 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;
*
* 以下代码将由 /path/to/packages/foo-bar/tests/Qux/QuuxTest.php
* 载入 \Foo\Bar\Qux\QuuxTest 类
*
* <?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 $prefixes = array();
/**
* 在 SPL 自动加载器栈中注册加载器
*
* @return void
*/
public function register()
{
spl_autoload_register(array($this, 'loadClass'));
}
/**
* 添加命名空间前缀与文件基目录对
*
* @param string $prefix 命名空间前缀
* @param string $base_dir 命名空间中类文件的基目录
* @param bool $prepend 为 True 时，将基目录插到最前，这将让其作为第一个被搜索到，否则插到将最后。
* @return void
*/
public function addNamespace($prefix, $base_dir, $prepend = false)
{
// 规范化命名空间前缀
$prefix = trim($prefix, '\\') . '\\';
// 规范化文件基目录
$base_dir = rtrim($base_dir, '/') . DIRECTORY_SEPARATOR;
$base_dir = rtrim($base_dir, DIRECTORY_SEPARATOR) . '/';
// 初始化命名空间前缀数组
if (isset($this->prefixes[$prefix]) === false) {
$this->prefixes[$prefix] = array();
}
// 将命名空间前缀与文件基目录对插入保存数组
if ($prepend) {
array_unshift($this->prefixes[$prefix], $base_dir);
} else {
array_push($this->prefixes[$prefix], $base_dir);
}
}
/**
* 由类名载入相应类文件
*
* @param string $class 完整的类名
* @return mixed 成功载入则返回载入的文件名，否则返回布尔 false
*/
public function loadClass($class)
{
// 当前命名空间前缀
$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, '\\');
}
// 找不到相应文件
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('\\', '/', $relative_class)
. '.php';
// 当文件存在时，在入之
if ($this->requireFile($file)) {
// 完成载入
return $file;
}
}
// 找不到相应文件
return false;
}
/**
* 当文件存在，则从文件系统载入之
*
* @param string $file 需要载入的文件
* @return bool 当文件存在则为 True，否则为 false
*/
protected function requireFile($file)
{
if (file_exists($file)) {
require $file;
return true;
}
return false;
}
}以下是上面代码单元测试的一种实现：
<?php
namespace Example\Tests;
class MockPsr4AutoloaderClass extends Psr4AutoloaderClass
{
protected $files = array();
public function setFiles(array $files)
{
$this->files = $files;
}
protected function requireFile($file)
{
return in_array($file, $this->files);
}
}
class Psr4AutoloaderClassTest extends \PHPUnit_Framework_TestCase
{
protected $loader;
protected function setUp()
{
$this->loader = new MockPsr4AutoloaderClass;
$this->loader->setFiles(array(
'/vendor/foo.bar/src/ClassName.php',
'/vendor/foo.bar/src/DoomClassName.php',
'/vendor/foo.bar/tests/ClassNameTest.php',
'/vendor/foo.bardoom/src/ClassName.php',
'/vendor/foo.bar.baz.dib/src/ClassName.php',
'/vendor/foo.bar.baz.dib.zim.gir/src/ClassName.php',
));
$this->loader->addNamespace(
'Foo\Bar',
'/vendor/foo.bar/src'
);
$this->loader->addNamespace(
'Foo\Bar',
'/vendor/foo.bar/tests'
);
$this->loader->addNamespace(
'Foo\BarDoom',
'/vendor/foo.bardoom/src'
);
$this->loader->addNamespace(
'Foo\Bar\Baz\Dib',
'/vendor/foo.bar.baz.dib/src'
);
$this->loader->addNamespace(
'Foo\Bar\Baz\Dib\Zim\Gir',
'/vendor/foo.bar.baz.dib.zim.gir/src'
);
}
public function testExistingFile()
{
$actual = $this->loader->loadClass('Foo\Bar\ClassName');
$expect = '/vendor/foo.bar/src/ClassName.php';
$this->assertSame($expect, $actual);
$actual = $this->loader->loadClass('Foo\Bar\ClassNameTest');
$expect = '/vendor/foo.bar/tests/ClassNameTest.php';
$this->assertSame($expect, $actual);
}
public function testMissingFile()
{
$actual = $this->loader->loadClass('No_Vendor\No_Package\NoClass');
$this->assertFalse($actual);
}
public function testDeepFile()
{
$actual = $this->loader->loadClass('Foo\Bar\Baz\Dib\Zim\Gir\ClassName');
$expect = '/vendor/foo.bar.baz.dib.zim.gir/src/ClassName.php';
$this->assertSame($expect, $actual);
}
public function testConfusion()
{
$actual = $this->loader->loadClass('Foo\Bar\DoomClassName');
$expect = '/vendor/foo.bar/src/DoomClassName.php';
$this->assertSame($expect, $actual);
$actual = $this->loader->loadClass('Foo\BarDoom\ClassName');
$expect = '/vendor/foo.bardoom/src/ClassName.php';
$this->assertSame($expect, $actual);
}
}