PHP CI框架中如何实现类库的自动加载及别名逻辑处理

缘由

app/controllers/Index.php中有如下代码

public function disable(){
        $this->yredis->set('name','tb');
        var_dump($this->yredis->get('name'));
        $this->load->view('welcome_message');
    }

发现这个yredis没有load，怎么来的？翻翻手册，有自动加载配置

在app/config/autoload.php中配置，部分内容如下

| -------------------------------------------------------------------
|  Auto-load Libraries
| -------------------------------------------------------------------
| These are the classes located in system/libraries/ or your
| application/libraries/ directory, with the addition of the
| 'database' library, which is somewhat of a special case.
|
| Prototype:
|
|    $autoload['libraries'] = array('database', 'email', 'session');
|
| You can also supply an alternative library name to be assigned
| in the controller:
|
|    $autoload['libraries'] = array('user_agent' => 'ua');
*/
$autoload['libraries'] = array('Yredis','validation'=>'sn');

追踪一下

那么他这个自动加载是在代码内如何实现的呢？肯定从头$CI大对象来看。
在system/core/Controller.php中，有如下两句

$this->load =& load_class('Loader', 'core');
$this->load->initialize();

通过common.php中定义的load_class方法，加载了loader类。不得不说ci的核心基本都在这里了。（这个load还是个未定义的属性么...？）
我们去看system/core/Loader.php中的initialize方法，不过load的时候肯定是先加载__construct方法

public function __construct()
    {
        // （ob机制，不要乱配~） 
        $this->_ci_ob_level = ob_get_level();
      
        $this->_ci_classes =& is_loaded();

        log_message('info', 'Loader Class Initialized');
    }

再回来看当前文件的initialize方法：

    public function initialize()
    {
        $this->_ci_autoloader();
    }

再去看_ci_autoloader...

    protected function _ci_autoloader()
    {
        if (file_exists(APPPATH.'config/autoload.php'))
        {
            include(APPPATH.'config/autoload.php');
        }

        if (file_exists(APPPATH.'config/'.ENVIRONMENT.'/autoload.php'))
        {
            include(APPPATH.'config/'.ENVIRONMENT.'/autoload.php');
        }

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

        // Autoload packages
        if (isset($autoload['packages']))
        {
            foreach ($autoload['packages'] as $package_path)
            {
                $this->add_package_path($package_path);
            }
        }

        // Load any custom config file
        if (count($autoload['config']) > 0)
        {
            foreach ($autoload['config'] as $val)
            {
                $this->config($val);
            }
        }

        // Autoload helpers and languages
        foreach (array('helper', 'language') as $type)
        {
            if (isset($autoload[$type]) && count($autoload[$type]) > 0)
            {
                $this->$type($autoload[$type]);
            }
        }

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

        // Load libraries
        if (isset($autoload['libraries']) && count($autoload['libraries']) > 0)
        {
            // Load the database driver.
            if (in_array('database', $autoload['libraries']))
            {
                $this->database();
                $autoload['libraries'] = array_diff($autoload['libraries'], array('database'));
            }


            // Load all other libraries
            $this->library($autoload['libraries']);
        }

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

这里总算有点眉目，定位到了加载开头配置的autoload.php的位置，
include(APPPATH.'config/autoload.php');
不难得出，是分别处理配置段的packages，config，helper，language，dirvers，libraries(包含database在内)，我们只是看library，于是定位到

$this->library($autoload['libraries']);

这里，看library方法

public function library($library, $params = NULL, $object_name = NULL)
    {
        if (empty($library))
        {
            return $this;
        }
        elseif (is_array($library))
        {
            foreach ($library as $key => $value)
            {
                if (is_int($key))
                {
                    $this->library($value, $params);
                }
                else
                {
                    $this->library($key, $params, $value);
                }
            }

            return $this;
        }

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

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

froeach中的if else 就是判断是否使用了别名，就像开头在autoload.php 中配置
$autoload['libraries'] = array('Yredis','validation'=>'sn');的第二个参数那样，这样我们在项目中可以显示使用$this->sn->xx()执行了。当然到这还没完，虽然最后返回的是$this,但是之前执行了关键的一步

$this->_ci_load_library($library, $params, $object_name);

我们继续看_ci_load_library方法

 protected function _ci_load_library($class, $params = NULL, $object_name = NULL)
    {
        // Get the class name, and while we're at it trim any slashes.
        // The directory path can be included as part of the class name,
        // but we don't want a leading slash
        $class = str_replace('.php', '', trim($class, '/'));

        // Was the path included with the class name?
        // We look for a slash to determine this
        if (($last_slash = strrpos($class, '/')) !== FALSE)
        {
            // Extract the path
            $subdir = substr($class, 0, ++$last_slash);

            // Get the filename from the path
            $class = substr($class, $last_slash);
        }
        else
        {
            $subdir = '';
        }

        $class = ucfirst($class);

        // Is this a stock library? There are a few special conditions if so ...
        if (file_exists(BASEPATH.'libraries/'.$subdir.$class.'.php'))
        {
            return $this->_ci_load_stock_library($class, $subdir, $params, $object_name);
        }

        // Safety: Was the class already loaded by a previous call?
        if (class_exists($class, FALSE))
        {
            $property = $object_name;
            if (empty($property))
            {
                $property = strtolower($class);
                isset($this->_ci_varmap[$property]) && $property = $this->_ci_varmap[$property];
            }

            $CI =& get_instance();
            if (isset($CI->$property))
            {
                log_message('debug', $class.' class already loaded. Second attempt ignored.');
                return;
            }

            return $this->_ci_init_library($class, '', $params, $object_name);
        }

        // Let's search for the requested library file and load it.
        foreach ($this->_ci_library_paths as $path)
        {
            // BASEPATH has already been checked for
            if ($path === BASEPATH)
            {
                continue;
            }

            $filepath = $path.'libraries/'.$subdir.$class.'.php';
            // Does the file exist? No? Bummer...
            if ( ! file_exists($filepath))
            {
                continue;
            }

            include_once($filepath);
            return $this->_ci_init_library($class, '', $params, $object_name);
        }

        // One last attempt. Maybe the library is in a subdirectory, but it wasn't specified?
        if ($subdir === '')
        {
            return $this->_ci_load_library($class.'/'.$class, $params, $object_name);
        }

        // If we got this far we were unable to find the requested class.
        log_message('error', 'Unable to load the requested class: '.$class);
        show_error('Unable to load the requested class: '.$class);
    }

大家可以看多个return的前导条件，我们最后追到_ci_init_library方法。如下：

protected function _ci_init_library($class, $prefix, $config = FALSE, $object_name = NULL)
    {
        // Is there an associated config file for this class? Note: these should always be lowercase
        if ($config === NULL)
        {
            // Fetch the config paths containing any package paths
            $config_component = $this->_ci_get_component('config');

            if (is_array($config_component->_config_paths))
            {
                $found = FALSE;
                foreach ($config_component->_config_paths as $path)
                {
                    // We test for both uppercase and lowercase, for servers that
                    // are case-sensitive with regard to file names. Load global first,
                    // override with environment next
                    if (file_exists($path.'config/'.strtolower($class).'.php'))
                    {
                        include($path.'config/'.strtolower($class).'.php');
                        $found = TRUE;
                    }
                    elseif (file_exists($path.'config/'.ucfirst(strtolower($class)).'.php'))
                    {
                        include($path.'config/'.ucfirst(strtolower($class)).'.php');
                        $found = TRUE;
                    }

                    if (file_exists($path.'config/'.ENVIRONMENT.'/'.strtolower($class).'.php'))
                    {
                        include($path.'config/'.ENVIRONMENT.'/'.strtolower($class).'.php');
                        $found = TRUE;
                    }
                    elseif (file_exists($path.'config/'.ENVIRONMENT.'/'.ucfirst(strtolower($class)).'.php'))
                    {
                        include($path.'config/'.ENVIRONMENT.'/'.ucfirst(strtolower($class)).'.php');
                        $found = TRUE;
                    }

                    // Break on the first found configuration, thus package
                    // files are not overridden by default paths
                    if ($found === TRUE)
                    {
                        break;
                    }
                }
            }
        }

        $class_name = $prefix.$class;

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

        // Set the variable name we will assign the class to
        // Was a custom class name supplied? If so we'll use it
        if (empty($object_name))
        {
            $object_name = strtolower($class);
            if (isset($this->_ci_varmap[$object_name]))
            {
                $object_name = $this->_ci_varmap[$object_name];
            }
        }

        // Don't overwrite existing properties
        $CI =& get_instance();
        if (isset($CI->$object_name))
        {
            if ($CI->$object_name instanceof $class_name)
            {
                log_message('debug', $class_name." has already been instantiated as '".$object_name."'. Second attempt aborted.");
                return;
            }

            show_error("Resource '".$object_name."' already exists and is not a ".$class_name." instance.");
        }

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

        var_dump($class);

        // Instantiate the class
        $CI->$object_name = isset($config)
            ? new $class_name($config)
            : new $class_name();
    }

注意多条件下的大小写处理（strtolower，ucfirst），等想出坑（如果有）的时候别忘记这里就好。走到最后就是这关键货

$CI->$object_name = isset($config)
? new $class_name($config)
: new $class_name();

到这里就很清楚了，最后参考CI大对象，输出部分如下

    //...
    ["load"]=>
  &object(Api_Loader)#13 (12) {
    ["_ci_services_paths":protected]=>
    array(1) {
      [0]=>
      string(45) "/usr/share/nginx/xin_mount_dev/trunk/app/"
    }
    ["_ci_services":protected]=>
    array(0) {
    }
    ["_ci_ob_level":protected]=>
    int(1)
    ["_ci_view_paths":protected]=>
    array(1) {
      ["/usr/share/nginx/xin_mount_dev/trunk/app/views/"]=>
      bool(true)
    }
    ["_ci_library_paths":protected]=>
    array(2) {
      [0]=>
      string(45) "/usr/share/nginx/xin_mount_dev/trunk/app/"
      [1]=>
      string(24) "/usr/share/nginx/ci_3.0/"
    }
    ["_ci_model_paths":protected]=>
    array(1) {
      [0]=>
      string(45) "/usr/share/nginx/xin_mount_dev/trunk/app/"
    }
    ["_ci_helper_paths":protected]=>
    array(2) {
      [0]=>
      string(45) "/usr/share/nginx/xin_mount_dev/trunk/app/"
      [1]=>
      string(24) "/usr/share/nginx/ci_3.0/"
    }
    ["_ci_cached_vars":protected]=>
    array(0) {
    }
    ["_ci_classes":protected]=>
    &array(15) {
      ["benchmark"]=>
      string(9) "Benchmark"
      ["hooks"]=>
      string(5) "Hooks"
      ["config"]=>
      string(6) "Config"
      ["log"]=>
      string(3) "Log"
      ["utf8"]=>
      string(4) "Utf8"
      ["uri"]=>
      string(3) "URI"
      ["router"]=>
      string(6) "Router"
      ["output"]=>
      string(6) "Output"
      ["security"]=>
      string(8) "Security"
      ["input"]=>
      string(5) "Input"
      ["lang"]=>
      string(4) "Lang"
      ["loader"]=>
      string(6) "Loader"
      ["yredis"]=>
      string(6) "Yredis"
      ["sn"]=>
      string(10) "Validation"
    }
    ["_ci_models":protected]=>
    array(0) {
    }
    ["_ci_helpers":protected]=>
    array(0) {
    }
    ["_ci_varmap":protected]=>
    array(2) {
      ["unit_test"]=>
      string(4) "unit"
      ["user_agent"]=>
      string(5) "agent"
    }
  }
  ["yredis"]=>
  object(Yredis)#14 (2) {
    ["_redis":"Yredis":private]=>
    object(Redis)#15 (0) {
    }
    ["_redis_conf":"Yredis":private]=>
    array(2) {
      ["hostname"]=>
      string(9) "127.0.0.1"
      ["port"]=>
      string(4) "6379"
    }
  }
  ["sn"]=>
  object(Validation)#16 (6)
  // ...

关注yredis和sn就更清楚啦,注意sn是别名，而实际指向的是Validation这个类

结束