How can I serialize zend_http_request object?

[xhe]

I am now meeting a problem. I need to save user's action and replay
these action later.
What I am planing is to serializa user's http_request object into
database and then later, user zend_front controller to dispatch this
request. It sounds feasible at least. This is what I did:

Step 1. Saving request object:
I used
$str = serializa($this->_request) in controller A and then save it
into database as string

Step 2.
later I use
$request = unserialize($retrievedString) to get this http request back
then
$frontController = Zend_Controller_Front::getInstance();
$dispatcher = $frontController->getDispatcher();
$response = new Zend_Controller_Response_Http();
$dispatcher->dispatch($request,$response);

to replay this request.

But I got error. it seemed the $request can not be successfully
restored back. The $request is not an zend_controller_request object
at all.

Can anyone tell me how to succesfully serialize
zend_controller_request_http object?

Thanks
Thanks