You can configure autoloading inside your Module_Bootstrap (almost same approach as in Benjamin Cremer's answer but module based).
To do it - create file Bootstrap.php in /modules/admin folder with the following content:
class Admin_Bootstrap extends Zend_Application_Module_Bootstrap
{
protected function _initAutoload()
{
$resourceLoader = new Zend_Loader_Autoloader_Resource(array(
'basePath' => realpath(dirname(__FILE__)),
'namespace' => 'Admin',
'resourceTypes' => array(
'api' => array(
'path' => 'api/',
'namespace' => 'Api'
)
)
));
$autoloader = new Zend_Application_Module_Autoloader(array(
'namespace' => 'Admin',
'basePath' => dirname(__FILE__),
'resourceloader' => $resourceLoader
));
return $autoloader;
}
}
After that you'll be able to instantiate class Admin_Api_Core etc. (you should specify all resoursTypes). If you have many modules, you can create such bootstraps for all of them.