CI框架 -- 核心文件 之 Loader.php（加载器）

顾名思义，装载器就是加载元素的，使用CI时，经常加载的有：

加载类库文件：$this->load->library()

 

加载视图文件：$this->load->view()

 

加载模型文件：$this->load->model()

 

加载数据库文件：$this->load->database()

 

加载帮助文件：$this->load->helper()

 

加载配置文件：$this->load->config()

 

加载包路径：$this->load->add_package_path()

 

源码：

 /**
  * Loader Class
  *
  * 用户加载views和files，常见的函数有model(),view(),library(),helper()
  *
  * Controller的好助手，$this->load =& load_class('Loader', 'core');，加载了loader，Controller就无比强大了
  * @link http://www.phpddt.com
  */
 class CI_Loader {

     protected $_ci_ob_level;

     protected $_ci_view_paths        = array();
     protected $_ci_library_paths    = array();
     protected $_ci_model_paths        = array();
     protected $_ci_helper_paths        = array();

     protected $_base_classes        = array(); // Set by the controller class

     protected $_ci_cached_vars        = array();

     protected $_ci_classes            = array();

     protected $_ci_loaded_files        = array();

     protected $_ci_models            = array();

     protected $_ci_helpers            = array();

     protected $_ci_varmap            = array('unit_test' => 'unit',
                                             'user_agent' => 'agent');

     public function __construct()
     {
                 //获取缓冲嵌套级别
         $this->_ci_ob_level  = ob_get_level();
         //library路径
                 $this->_ci_library_paths = array(APPPATH, BASEPATH);
                 //helper路径
         $this->_ci_helper_paths = array(APPPATH, BASEPATH);
                 //model路径
         $this->_ci_model_paths = array(APPPATH);
                 //view路径
         $this->_ci_view_paths = array(APPPATH.'views/'    => TRUE);

         log_message('debug', "Loader Class Initialized");
     }

     // --------------------------------------------------------------------

     /**
      * 初始化Loader
      *
      */
     public function initialize()
     {
         $this->_ci_classes = array();
         $this->_ci_loaded_files = array();
         $this->_ci_models = array();
                 //将is_loaded（common中记录加载核心类函数）加载的核心类交给_base_classes
         $this->_base_classes =& is_loaded();

                 //加载autoload.php配置中文件
         $this->_ci_autoloader();

         return $this;
     }

     // --------------------------------------------------------------------

     /**
      * 检测类是否加载
      */
     public function is_loaded($class)
     {
         if (isset($this->_ci_classes[$class]))
         {
             return $this->_ci_classes[$class];
         }

         return FALSE;
     }

     // --------------------------------------------------------------------

     /**
      * 加载Class
      */
     public function library($library = '', $params = NULL, $object_name = NULL)
     {
         if (is_array($library))
         {
             foreach ($library as $class)
             {
                 $this->library($class, $params);
             }

             return;
         }

                 //如果$library为空或者已经加载。。。
         if ($library == '' OR isset($this->_base_classes[$library]))
         {
             return FALSE;
         }

         if ( ! is_null($params) && ! is_array($params))
         {
             $params = NULL;
         }

         $this->_ci_load_class($library, $params, $object_name);
     }

     // --------------------------------------------------------------------

     /**
      * 加载和实例化model
      */
     public function model($model, $name = '', $db_conn = FALSE)
     {
                 //CI支持数组加载多个model
         if (is_array($model))
         {
             foreach ($model as $babe)
             {
                 $this->model($babe);
             }
             return;
         }

         if ($model == '')
         {
             return;
         }

         $path = '';

         // 是否存在子目录
         if (($last_slash = strrpos($model, '/')) !== FALSE)
         {
             // The path is in front of the last slash
             $path = substr($model, 0, $last_slash + 1);

             // And the model name behind it
             $model = substr($model, $last_slash + 1);
         }

         if ($name == '')
         {
             $name = $model;
         }

         if (in_array($name, $this->_ci_models, TRUE))
         {
             return;
         }

         $CI =& get_instance();
         if (isset($CI->$name))
         {
             show_error('The model name you are loading is the name of a resource that is already being used: '.$name);
         }

         $model = strtolower($model); //model文件名全小写

         foreach ($this->_ci_model_paths as $mod_path)
         {
             if ( ! file_exists($mod_path.'models/'.$path.$model.'.php'))
             {
                 continue;
             }

             if ($db_conn !== FALSE AND ! class_exists('CI_DB'))
             {
                 if ($db_conn === TRUE)
                 {
                     $db_conn = '';
                 }

                 $CI->load->database($db_conn, FALSE, TRUE);
             }

             if ( ! class_exists('CI_Model'))
             {
                 load_class('Model', 'core');
             }

             require_once($mod_path.'models/'.$path.$model.'.php');

             $model = ucfirst($model);

             $CI->$name = new $model();
                         //保存在Loader::_ci_models中，以后可以用它来判断某个model是否已经加载过。
             $this->_ci_models[] = $name;
             return;
         }

         // couldn't find the model
         show_error('Unable to locate the model you have specified: '.$model);
     }

     // --------------------------------------------------------------------

     /**
      * 数据库Loader
      */
     public function database($params = '', $return = FALSE, $active_record = NULL)
     {
         // Grab the super object
         $CI =& get_instance();

         // 是否需要加载db
         if (class_exists('CI_DB') AND $return == FALSE AND $active_record == NULL AND isset($CI->db) AND is_object($CI->db))
         {
             return FALSE;
         }

         require_once(BASEPATH.'database/DB.php');

         if ($return === TRUE)
         {
             return DB($params, $active_record);
         }

         // Initialize the db variable.  Needed to prevent
         // reference errors with some configurations
         $CI->db = '';

         // Load the DB class
         $CI->db =& DB($params, $active_record);
     }

     // --------------------------------------------------------------------

     /**
      * 加载数据库工具类
      */
     public function dbutil()
     {
         if ( ! class_exists('CI_DB'))
         {
             $this->database();
         }

         $CI =& get_instance();

         // for backwards compatibility, load dbforge so we can extend dbutils off it
         // this use is deprecated and strongly discouraged
         $CI->load->dbforge();

         require_once(BASEPATH.'database/DB_utility.php');
         require_once(BASEPATH.'database/drivers/'.$CI->db->dbdriver.'/'.$CI->db->dbdriver.'_utility.php');
         $class = 'CI_DB_'.$CI->db->dbdriver.'_utility';

         $CI->dbutil = new $class();
     }

     // --------------------------------------------------------------------

     /**
      * Load the Database Forge Class
      *
      * @return    string
      */
     public function dbforge()
     {
         if ( ! class_exists('CI_DB'))
         {
             $this->database();
         }

         $CI =& get_instance();

         require_once(BASEPATH.'database/DB_forge.php');
         require_once(BASEPATH.'database/drivers/'.$CI->db->dbdriver.'/'.$CI->db->dbdriver.'_forge.php');
         $class = 'CI_DB_'.$CI->db->dbdriver.'_forge';

         $CI->dbforge = new $class();
     }

     // --------------------------------------------------------------------

     /**
      * 加载视图文件
      */
     public function view($view, $vars = array(), $return = FALSE)
     {
         return $this->_ci_load(array('_ci_view' => $view, '_ci_vars' => $this->_ci_object_to_array($vars), '_ci_return' => $return));
     }

     // --------------------------------------------------------------------

     /**
      * 加载普通文件
      */
     public function file($path, $return = FALSE)
     {
         return $this->_ci_load(array('_ci_path' => $path, '_ci_return' => $return));
     }

     // --------------------------------------------------------------------

     /**
      * 设置变量
      *
      * Once variables are set they become available within
      * the controller class and its "view" files.
      *
      */
     public function vars($vars = array(), $val = '')
     {
         if ($val != '' AND is_string($vars))
         {
             $vars = array($vars => $val);
         }

         $vars = $this->_ci_object_to_array($vars);

         if (is_array($vars) AND count($vars) > 0)
         {
             foreach ($vars as $key => $val)
             {
                 $this->_ci_cached_vars[$key] = $val;
             }
         }
     }

     // --------------------------------------------------------------------

     /**
      * 检查并获取变量
      */
     public function get_var($key)
     {
         return isset($this->_ci_cached_vars[$key]) ? $this->_ci_cached_vars[$key] : NULL;
     }

     // --------------------------------------------------------------------

     /**
      * 加载helper
      */
     public function helper($helpers = array())
     {
         foreach ($this->_ci_prep_filename($helpers, '_helper') as $helper)
         {
             if (isset($this->_ci_helpers[$helper]))
             {
                 continue;
             }

             $ext_helper = APPPATH.'helpers/'.config_item('subclass_prefix').$helper.'.php';

             // 如果是扩展helper的话
             if (file_exists($ext_helper))
             {
                 $base_helper = BASEPATH.'helpers/'.$helper.'.php';

                 if ( ! file_exists($base_helper))
                 {
                     show_error('Unable to load the requested file: helpers/'.$helper.'.php');
                 }

                 include_once($ext_helper);
                 include_once($base_helper);

                 $this->_ci_helpers[$helper] = TRUE;
                 log_message('debug', 'Helper loaded: '.$helper);
                 continue;
             }

             // 如果不是扩展helper，helper路径中加载helper
             foreach ($this->_ci_helper_paths as $path)
             {
                 if (file_exists($path.'helpers/'.$helper.'.php'))
                 {
                     include_once($path.'helpers/'.$helper.'.php');

                     $this->_ci_helpers[$helper] = TRUE;
                     log_message('debug', 'Helper loaded: '.$helper);
                     break;
                 }
             }

             // 如果该helper还没加载成功的话，说明加载helper失败
             if ( ! isset($this->_ci_helpers[$helper]))
             {
                 show_error('Unable to load the requested file: helpers/'.$helper.'.php');
             }
         }
     }

     // --------------------------------------------------------------------

     /**
      * 可以看到helpers调用也是上面的helper,只是helpers的别名而已
      */
     public function helpers($helpers = array())
     {
         $this->helper($helpers);
     }

     // --------------------------------------------------------------------

     /**
      * 加载language文件
      */
     public function language($file = array(), $lang = '')
     {
         $CI =& get_instance();

         if ( ! is_array($file))
         {
             $file = array($file);
         }

         foreach ($file as $langfile)
         {
             $CI->lang->load($langfile, $lang);
         }
     }

     // --------------------------------------------------------------------

     /**
      * 加载配置文件
      */
     public function config($file = '', $use_sections = FALSE, $fail_gracefully = FALSE)
     {
         $CI =& get_instance();
         $CI->config->load($file, $use_sections, $fail_gracefully);
     }

     // --------------------------------------------------------------------

     /**
      * Driver
      *
      * 加载 driver library
      */
     public function driver($library = '', $params = NULL, $object_name = NULL)
     {
         if ( ! class_exists('CI_Driver_Library'))
         {
             // we aren't instantiating an object here, that'll be done by the Library itself
             require BASEPATH.'libraries/Driver.php';
         }

         if ($library == '')
         {
             return FALSE;
         }

         // We can save the loader some time since Drivers will *always* be in a subfolder,
         // and typically identically named to the library
         if ( ! strpos($library, '/'))
         {
             $library = ucfirst($library).'/'.$library;
         }

         return $this->library($library, $params, $object_name);
     }

     // --------------------------------------------------------------------

     /**
      * 添加 Package 路径
      *
      * 把package路径添加到库，模型，助手，配置路径
      */
     public function add_package_path($path, $view_cascade=TRUE)
     {
         $path = rtrim($path, '/').'/';

         array_unshift($this->_ci_library_paths, $path);
         array_unshift($this->_ci_model_paths, $path);
         array_unshift($this->_ci_helper_paths, $path);

         $this->_ci_view_paths = array($path.'views/' => $view_cascade) + $this->_ci_view_paths;

         $config =& $this->_ci_get_component('config');
         array_unshift($config->_config_paths, $path);
     }

     // --------------------------------------------------------------------

     /**
      * 获取Package Paths，默认不包含BASEPATH
      */
     public function get_package_paths($include_base = FALSE)
     {
         return $include_base === TRUE ? $this->_ci_library_paths : $this->_ci_model_paths;
     }

     // --------------------------------------------------------------------

     /**
      * 剔除Package Path
      *
      * Remove a path from the library, model, and helper path arrays if it exists
      * If no path is provided, the most recently added path is removed.
      *
      */
     public function remove_package_path($path = '', $remove_config_path = TRUE)
     {
         $config =& $this->_ci_get_component('config');

         if ($path == '')
         {
             $void = array_shift($this->_ci_library_paths);
             $void = array_shift($this->_ci_model_paths);
             $void = array_shift($this->_ci_helper_paths);
             $void = array_shift($this->_ci_view_paths);
             $void = array_shift($config->_config_paths);
         }
         else
         {
             $path = rtrim($path, '/').'/';
             foreach (array('_ci_library_paths', '_ci_model_paths', '_ci_helper_paths') as $var)
             {
                 if (($key = array_search($path, $this->{$var})) !== FALSE)
                 {
                     unset($this->{$var}[$key]);
                 }
             }

             if (isset($this->_ci_view_paths[$path.'views/']))
             {
                 unset($this->_ci_view_paths[$path.'views/']);
             }

             if (($key = array_search($path, $config->_config_paths)) !== FALSE)
             {
                 unset($config->_config_paths[$key]);
             }
         }

         // 保证应用默认的路径依然存在
         $this->_ci_library_paths = array_unique(array_merge($this->_ci_library_paths, array(APPPATH, BASEPATH)));
         $this->_ci_helper_paths = array_unique(array_merge($this->_ci_helper_paths, array(APPPATH, BASEPATH)));
         $this->_ci_model_paths = array_unique(array_merge($this->_ci_model_paths, array(APPPATH)));
         $this->_ci_view_paths = array_merge($this->_ci_view_paths, array(APPPATH.'views/' => TRUE));
         $config->_config_paths = array_unique(array_merge($config->_config_paths, array(APPPATH)));
     }

     // --------------------------------------------------------------------

     /**
      * Loader
      *
      * This function is used to load views and files.
      * Variables are prefixed with _ci_ to avoid symbol collision with
      * variables made available to view files
      *
      * @param    array
      * @return    void
      */
     protected function _ci_load($_ci_data)
     {
         // Set the default data variables
         foreach (array('_ci_view', '_ci_vars', '_ci_path', '_ci_return') as $_ci_val)
         {
             $$_ci_val = ( ! isset($_ci_data[$_ci_val])) ? FALSE : $_ci_data[$_ci_val];
         }

         $file_exists = FALSE;
                 //如果$_ci_path不为空，则说明当前要加载普通文件。Loader::file才会有path
         if ($_ci_path != '')
         {
             $_ci_x = explode('/', $_ci_path);
             $_ci_file = end($_ci_x);
         }
         else
         {
             $_ci_ext = pathinfo($_ci_view, PATHINFO_EXTENSION);
             $_ci_file = ($_ci_ext == '') ? $_ci_view.'.php' : $_ci_view;

             foreach ($this->_ci_view_paths as $view_file => $cascade)
             {
                 if (file_exists($view_file.$_ci_file))
                 {
                     $_ci_path = $view_file.$_ci_file;
                     $file_exists = TRUE;
                     break;
                 }

                 if ( ! $cascade)
                 {
                     break;
                 }
             }
         }
                 //view文件不存在则会报错
         if ( ! $file_exists && ! file_exists($_ci_path))
         {
             show_error('Unable to load the requested file: '.$_ci_file);
         }

         // 把CI的所有属性都传递给loader，view中$this指的是loader
         $_ci_CI =& get_instance();
         foreach (get_object_vars($_ci_CI) as $_ci_key => $_ci_var)
         {
             if ( ! isset($this->$_ci_key))
             {
                 $this->$_ci_key =& $_ci_CI->$_ci_key;
             }
         }

         /*
          * Extract and cache variables
          *
          * You can either set variables using the dedicated $this->load_vars()
          * function or via the second parameter of this function. We'll merge
          * the two types and cache them so that views that are embedded within
          * other views can have access to these variables.
          */

         if (is_array($_ci_vars))
         {
             $this->_ci_cached_vars = array_merge($this->_ci_cached_vars, $_ci_vars);
         }

         extract($this->_ci_cached_vars);

         /*
          * 将视图内容放到缓存区
          *
          */
         ob_start();

         // 支持短标签
         if ((bool) @ini_get('short_open_tag') === FALSE AND config_item('rewrite_short_tags') == TRUE)
         {
             echo eval('?>'.preg_replace("/;*\s*\?>/", "; ?>", str_replace('<?=', '<?php echo ', file_get_contents($_ci_path))));
         }
         else
         {
             include($_ci_path); // include() vs include_once() allows for multiple views with the same name
         }

         log_message('debug', 'File loaded: '.$_ci_path);

         // 是否直接返回view数据
         if ($_ci_return === TRUE)
         {
             $buffer = ob_get_contents();
             @ob_end_clean();
             return $buffer;
         }

         //当前这个视图文件是被另一个视图文件通过$this->view()方法引入，即视图文件嵌入视图文件
         if (ob_get_level() > $this->_ci_ob_level + 1)
         {

             ob_end_flush();
         }
         else
         {       ////把缓冲区的内容交给Output组件并清空关闭缓冲区。
             $_ci_CI->output->append_output(ob_get_contents());
             @ob_end_clean();
         }
     }

     // --------------------------------------------------------------------

     /**
      * 加载类
      */
     protected function _ci_load_class($class, $params = NULL, $object_name = NULL)
     {
         // 去掉.php和两端的/获取的$class就是类名或目录名+类名
         $class = str_replace('.php', '', trim($class, '/'));

         // CI允许dir/filename方式
         $subdir = '';
         if (($last_slash = strrpos($class, '/')) !== FALSE)
         {
             // 目录
             $subdir = substr($class, 0, $last_slash + 1);

             // 文件名
             $class = substr($class, $last_slash + 1);
         }

         // 允许加载的类名首字母大写或全小写
         foreach (array(ucfirst($class), strtolower($class)) as $class)
         {
             $subclass = APPPATH.'libraries/'.$subdir.config_item('subclass_prefix').$class.'.php';

             // 是否是扩展类
             if (file_exists($subclass))
             {
                 $baseclass = BASEPATH.'libraries/'.ucfirst($class).'.php';

                 if ( ! file_exists($baseclass))
                 {
                     log_message('error', "Unable to load the requested class: ".$class);
                     show_error("Unable to load the requested class: ".$class);
                 }

                 // Safety:  Was the class already loaded by a previous call?
                 if (in_array($subclass, $this->_ci_loaded_files))
                 {
                     // Before we deem this to be a duplicate request, let's see
                     // if a custom object name is being supplied.  If so, we'll
                     // return a new instance of the object
                     if ( ! is_null($object_name))
                     {
                         $CI =& get_instance();
                         if ( ! isset($CI->$object_name))
                         {
                             return $this->_ci_init_class($class, config_item('subclass_prefix'), $params, $object_name);
                         }
                     }

                     $is_duplicate = TRUE;
                     log_message('debug', $class." class already loaded. Second attempt ignored.");
                     return;
                 }

                 include_once($baseclass);
                 include_once($subclass);
                 $this->_ci_loaded_files[] = $subclass;
                                 //实例化类
                 return $this->_ci_init_class($class, config_item('subclass_prefix'), $params, $object_name);
             }

             // 如果不是扩展，和上面类似
             $is_duplicate = FALSE;
             foreach ($this->_ci_library_paths as $path)
             {
                 $filepath = $path.'libraries/'.$subdir.$class.'.php';

                 // Does the file exist?  No?  Bummer...
                 if ( ! file_exists($filepath))
                 {
                     continue;
                 }

                 // Safety:  Was the class already loaded by a previous call?
                 if (in_array($filepath, $this->_ci_loaded_files))
                 {
                     // Before we deem this to be a duplicate request, let's see
                     // if a custom object name is being supplied.  If so, we'll
                     // return a new instance of the object
                     if ( ! is_null($object_name))
                     {
                         $CI =& get_instance();
                         if ( ! isset($CI->$object_name))
                         {
                             return $this->_ci_init_class($class, '', $params, $object_name);
                         }
                     }

                     $is_duplicate = TRUE;
                     log_message('debug', $class." class already loaded. Second attempt ignored.");
                     return;
                 }

                 include_once($filepath);
                 $this->_ci_loaded_files[] = $filepath;
                 return $this->_ci_init_class($class, '', $params, $object_name);
             }

         } // END FOREACH

         // 如果还没有找到该class，最后的尝试是该class会不会在同名的子目录下
         if ($subdir == '')
         {
             $path = strtolower($class).'/'.$class;
             return $this->_ci_load_class($path, $params);
         }

         // 加载失败，报错
         if ($is_duplicate == FALSE)
         {
             log_message('error', "Unable to load the requested class: ".$class);
             show_error("Unable to load the requested class: ".$class);
         }
     }

     // --------------------------------------------------------------------

     /**
      * 实例化已经加载的类
      */
     protected function _ci_init_class($class, $prefix = '', $config = FALSE, $object_name = NULL)
     {
         // 是否有类的配置信息
         if ($config === NULL)
         {
             // Fetch the config paths containing any package paths
             $config_component = $this->_ci_get_component('config');

             if (is_array($config_component->_config_paths))
             {
                 // Break on the first found file, thus package files
                 // are not overridden by default paths
                 foreach ($config_component->_config_paths as $path)
                 {
                     // We test for both uppercase and lowercase, for servers that
                     // are case-sensitive with regard to file names. Check for environment
                     // first, global next
                     if (defined('ENVIRONMENT') AND file_exists($path .'config/'.ENVIRONMENT.'/'.strtolower($class).'.php'))
                     {
                         include($path .'config/'.ENVIRONMENT.'/'.strtolower($class).'.php');
                         break;
                     }
                     elseif (defined('ENVIRONMENT') AND file_exists($path .'config/'.ENVIRONMENT.'/'.ucfirst(strtolower($class)).'.php'))
                     {
                         include($path .'config/'.ENVIRONMENT.'/'.ucfirst(strtolower($class)).'.php');
                         break;
                     }
                     elseif (file_exists($path .'config/'.strtolower($class).'.php'))
                     {
                         include($path .'config/'.strtolower($class).'.php');
                         break;
                     }
                     elseif (file_exists($path .'config/'.ucfirst(strtolower($class)).'.php'))
                     {
                         include($path .'config/'.ucfirst(strtolower($class)).'.php');
                         break;
                     }
                 }
             }
         }

         if ($prefix == '')
         {       //system下library
             if (class_exists('CI_'.$class))
             {
                 $name = 'CI_'.$class;
             }
             elseif (class_exists(config_item('subclass_prefix').$class))
             {       //扩展library
                 $name = config_item('subclass_prefix').$class;
             }
             else
             {
                 $name = $class;
             }
         }
         else
         {
             $name = $prefix.$class;
         }

         // Is the class name valid?
         if ( ! class_exists($name))
         {
             log_message('error', "Non-existent class: ".$name);
             show_error("Non-existent class: ".$class);
         }

         // Set the variable name we will assign the class to
         // Was a custom class name supplied?  If so we'll use it
         $class = strtolower($class);

         if (is_null($object_name))
         {
             $classvar = ( ! isset($this->_ci_varmap[$class])) ? $class : $this->_ci_varmap[$class];
         }
         else
         {
             $classvar = $object_name;
         }

         // Save the class name and object name
         $this->_ci_classes[$class] = $classvar;

         // 将初始化的类的实例给CI超级句柄
         $CI =& get_instance();
         if ($config !== NULL)
         {
             $CI->$classvar = new $name($config);
         }
         else
         {
             $CI->$classvar = new $name;
         }
     }

     // --------------------------------------------------------------------

     /**
      * 自动加载器
          *
          * autoload.php配置的自动加载文件有：
          *  | 1. Packages
             | 2. Libraries
             | 3. Helper files
             | 4. Custom config files
             | 5. Language files
             | 6. Models
      */
     private function _ci_autoloader()
     {
         if (defined('ENVIRONMENT') AND file_exists(APPPATH.'config/'.ENVIRONMENT.'/autoload.php'))
         {
             include(APPPATH.'config/'.ENVIRONMENT.'/autoload.php');
         }
         else
         {
             include(APPPATH.'config/autoload.php');
         }

         if ( ! isset($autoload))
         {
             return FALSE;
         }

         // 自动加载packages,也就是将package_path加入到library，model，helper，config
         if (isset($autoload['packages']))
         {
             foreach ($autoload['packages'] as $package_path)
             {
                 $this->add_package_path($package_path);
             }
         }

         // 加载config文件
         if (count($autoload['config']) > 0)
         {
             $CI =& get_instance();
             foreach ($autoload['config'] as $key => $val)
             {
                 $CI->config->load($val);
             }
         }

         // 加载helper和language
         foreach (array('helper', 'language') as $type)
         {
             if (isset($autoload[$type]) AND count($autoload[$type]) > 0)
             {
                 $this->$type($autoload[$type]);
             }
         }

         // 这个好像是为了兼容以前版本的
         if ( ! isset($autoload['libraries']) AND isset($autoload['core']))
         {
             $autoload['libraries'] = $autoload['core'];
         }

         // 加载libraries
         if (isset($autoload['libraries']) AND count($autoload['libraries']) > 0)
         {
             // 加载db
             if (in_array('database', $autoload['libraries']))
             {
                 $this->database();
                 $autoload['libraries'] = array_diff($autoload['libraries'], array('database'));
             }

             // 加载所有其他libraries
             foreach ($autoload['libraries'] as $item)
             {
                 $this->library($item);
             }
         }

         // Autoload models
         if (isset($autoload['model']))
         {
             $this->model($autoload['model']);
         }
     }

     // --------------------------------------------------------------------

     /**
      * 返回由对象属性组成的关联数组
      */
     protected function _ci_object_to_array($object)
     {
         return (is_object($object)) ? get_object_vars($object) : $object;
     }

     // --------------------------------------------------------------------

     /**
      * 获取CI某个组件的实例
      */
     protected function &_ci_get_component($component)
     {
         $CI =& get_instance();
         return $CI->$component;
     }

     // --------------------------------------------------------------------

     /**
      * 处理文件名，这个函数主要是返回正确文件名
      */
     protected function _ci_prep_filename($filename, $extension)
     {
         if ( ! is_array($filename))
         {
             return array(strtolower(str_replace('.php', '', str_replace($extension, '', $filename)).$extension));
         }
         else
         {
             foreach ($filename as $key => $val)
             {
                 $filename[$key] = strtolower(str_replace('.php', '', str_replace($extension, '', $val)).$extension);
             }

             return $filename;
         }
     }
 }