PHP管理依赖(dependency)关系工具 Composer的自动加载（autoload），dependencyautoload_PHP教程

{
 "require": {
  "monolog/monolog": "1.*"
 }
}

php composer.phar install

require '/path/to/vendor/autoload.php';

use MonologLogger;
use MonologHandlerStreamHandler;
// 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');

{
  "autoload": {
    "psr-4": {
      "Foo\": "src/",
    }
  }
}

{
  "autoload": {
    "psr-0": {
      "Foo\": "src/",
    }
  }
}

{
  "autoload": {
    "classmap": ["src/", "lib/", "Something.php"]
  }
}

{
  "autoload": {
    "files": ["src/MyLibrary/functions.php"]
  }
}

<?php
// autoload_real.php @generated by Composer
class ComposerAutoloaderInit73612b48e6c3d0de8d56e03dece61d11
{
  private static $loader;
  public static function loadClassLoader($class)
  {
 if ('ComposerAutoloadClassLoader' === $class) {
   require __DIR__ . '/ClassLoader.php';
 }
  }
  public static function getLoader()
  {
 if (null !== self::$loader) {
   return self::$loader;
 }
 spl_autoload_register(array('ComposerAutoloaderInit73612b48e6c3d0de8d56e03dece61d11', 'loadClassLoader'), true, true);
 self::$loader = $loader = new ComposerAutoloadClassLoader();
 spl_autoload_unregister(array('ComposerAutoloaderInit73612b48e6c3d0de8d56e03dece61d11', 'loadClassLoader'));
 $vendorDir = dirname(__DIR__); //verdor第三方类库提供者目录
 $baseDir = dirname($vendorDir); //整个应用的目录
 $includePaths = require __DIR__ . '/include_paths.php';
 array_push($includePaths, get_include_path());
 set_include_path(join(PATH_SEPARATOR, $includePaths));
 $map = require __DIR__ . '/autoload_namespaces.php';
 foreach ($map as $namespace => $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;
}

/**
  * @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;
}