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正文开始 <p>https://segmentfault.com/a/1190000000380008</p><p><br /></p><p></p><p><a rel="nofollow" href="http://www.php-fig.org/" target="_blank">FIG</a>制定的PHP规范，简称PSR，是PHP开发的事实标准。</p><p>PSR原本有四个规范，分别是：</p>PSR-0 自动加载PSR-1 基本代码规范PSR-2 代码样式PSR-3 日志接口<p>2013年底，新出了第5个规范——<a rel="nofollow" href="https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader.md" target="_blank">PSR-4</a>。</p><p>PSR-4规范了如何指定文件路径从而自动加载类定义，同时规范了自动加载文件的位置。这个乍一看和PSR-0重复了，实际上，在功能上确实有所重复。区别在于PSR-4的规范比较干净，去除了兼容PHP 5.3以前版本的内容，有一点PSR-0升级版的感觉。当然，PSR-4也不是要完全替代PSR-0，而是在必要的时候补充PSR-0——当然，如果你愿意，PSR-4也可以替代PSR-0。PSR-4可以和包括PSR-0在内的其他自动加载机制共同使用。</p><p>PSR-4和PSR-0最大的区别是对下划线（underscore)的定义不同。PSR-4中，在类名中使用下划线没有任何特殊含义。而PSR-0则规定类名中的下划线_会被转化成目录分隔符。</p>代码样例<p>以下代码展示了遵循PSR-4的类定义，这个类处理多个命名空间：</p><pre><?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 # FooBarBaz
* Qux/
* Quux.php # FooBarQuxQuux
* tests/
* BazTest.php # FooBarBazTest
* Qux/
* QuuxTest.php # FooBarQuxQuuxTest
*
* ... add the path to the class files for the FooBar namespace prefix
* as follows:
*
* <?php
* // instantiate the loader
* $loader = new ExamplePsr4AutoloaderClass;
*
* // register the autoloader
* $loader->register();
*
* // register the base directories for the namespace prefix
* $loader->addNamespace('FooBar', '/path/to/packages/foo-bar/src');
* $loader->addNamespace('FooBar', '/path/to/packages/foo-bar/tests');
*
* The following line would cause the autoloader to attempt to load the
* FooBarQuxQuux class from /path/to/packages/foo-bar/src/Qux/Quux.php:
*
* <?php
* new FooBarQuxQuux;
*
* The following line would cause the autoloader to attempt to load the
* FooBarQuxQuuxTest class from /path/to/packages/foo-bar/tests/Qux/QuuxTest.php:
*
* <?php
* new FooBarQuxQuuxTest;
*/
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;
}
}
</pre><p>相应的单元测试代码</p><pre><?php
namespace ExampleTests;
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(
'FooBar',
'/vendor/foo.bar/src'
);
$this->loader->addNamespace(
'FooBar',
'/vendor/foo.bar/tests'
);
$this->loader->addNamespace(
'FooBarDoom',
'/vendor/foo.bardoom/src'
);
$this->loader->addNamespace(
'FooBarBazDib',
'/vendor/foo.bar.baz.dib/src'
);
$this->loader->addNamespace(
'FooBarBazDibZimGir',
'/vendor/foo.bar.baz.dib.zim.gir/src'
);
}
public function testExistingFile()
{
$actual = $this->loader->loadClass('FooBarClassName');
$expect = '/vendor/foo.bar/src/ClassName.php';
$this->assertSame($expect, $actual);
$actual = $this->loader->loadClass('FooBarClassNameTest');
$expect = '/vendor/foo.bar/tests/ClassNameTest.php';
$this->assertSame($expect, $actual);
}
public function testMissingFile()
{
$actual = $this->loader->loadClass('No_VendorNo_PackageNoClass');
$this->assertFalse($actual);
}
public function testDeepFile()
{
$actual = $this->loader->loadClass('FooBarBazDibZimGirClassName');
$expect = '/vendor/foo.bar.baz.dib.zim.gir/src/ClassName.php';
$this->assertSame($expect, $actual);
}
public function testConfusion()
{
$actual = $this->loader->loadClass('FooBarDoomClassName');
$expect = '/vendor/foo.bar/src/DoomClassName.php';
$this->assertSame($expect, $actual);
$actual = $this->loader->loadClass('FooBarDoomClassName');
$expect = '/vendor/foo.bardoom/src/ClassName.php';
$this->assertSame($expect, $actual);
}
}
</pre>Composer<p>PHP的包管理系统<a rel="nofollow" href="http://segmentfault.com/a/1190000000353129">Composer</a>已经支持PSR-4，同时也允许在composer.json中定义不同的prefix使用不同的自动加载机制。</p><p>Composer使用PSR-0风格</p><pre>vendor/
vendor_name/
package_name/
src/
Vendor_Name/
Package_Name/
ClassName.php # Vendor_NamePackage_NameClassName
tests/
Vendor_Name/
Package_Name/
ClassNameTest.php # Vendor_NamePackage_NameClassName
</pre><p>Composer使用PSR-4风格</p><pre>vendor/
vendor_name/
package_name/
src/
ClassName.php # Vendor_NamePackage_NameClassName
tests/
ClassNameTest.php # Vendor_NamePackage_NameClassNameTest
</pre><p>对比以上两种结构，明显可以看出PSR-4带来更简洁的文件结构。</p><br />
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