Thanks for all your responses Don.
My problem is the next:
I want to generate a xml stream from Action. I don't know how to sent (Forward) this xml without using jsp, to cocoon with cocoon plugin.
Can you help me?
I have found the solution.
Firstable the cocoon plugin use cocoon 2.1.m2 and the stream generator only read parameters in the request parameters. In the last version of cocoon the stream generator has been modified. This generator read the parameter from request attribute. In the action I set in the correct attribute the xml document.