怎么自动加载类文件

function __autoload($className){
if(file_exists('model/'.$className.'.class.php')){
include_once('model/'.$className.'.class.php');
}
if(file_exists('Controller/'.$className.'.class.php')){
include_once('Controller/'.$className.'.class.php');
}

$prefix=$GLOBALS['groupName']=='main'?'':'../';
if(file_exists($prefix.'core/'.$className.'.class.php')){
include_once($prefix.'core/'.$className.'.class.php');
}
if(file_exists($prefix.'core/Smarty-3.1.6/'.$className.'.class.php')){
include_once($prefix.'core/Smarty-3.1.6/'.$className.'.class.php');
}
if(file_exists($prefix.'core/Smarty-3.1.6/sysplugins/'.$className.'.php')){
include_once($prefix.'core/Smarty-3.1.6/sysplugins/'.$className.'.php');
}

}

$arr = array('classPath1','classPath2','classPath3');
foreach($arr as $v){
  $new_path = $v.$className.'.php';
  if(file_exists($new_path)){
    include_once($new_path);
    break;
  }
}