Zend框架插件问题

Here is the content of file User.php

<?php 
class My_Controller_Plugin_User extends Zend_Controller_Plugin_Abstract
{
    public function preDispatch(Zend_Controller_Request_Abstract $request)
    {
        echo 'preDispatch is called';
    }
}

Which is located in library/My/Controller/Plugin/ folder.

In bootstrap.php I'm trying to register the plugin with this

$front = Zend_Controller_Front::getInstance();
  $front->registerPlugin(new My_Controller_Plugin_User);

but I get

Fatal error: Class 'My_Controller_Plugin_User' not found

as error. What I miss here ?

Zend_Loader_Autoloader::getInstance()->registerNamespace('My');

You can also put new namespaces to config.ini

autoloaderNamespaces[] = "Foo_"
autoloaderNamespaces[] = "Bar_"

ZF will load it automatically.