I found that in the servlet 2.4 specs.
---------- Forwarded message ----------
From: <Sebastien.Dionne_at_videotron.com>
Date: Apr 26, 2010 11:10 AM
Subject: servlet 2.4 specs
To: <survivant00_at_gmail.com>
Servlet programmers are responsible for ensuring that the Content-Type
header is appropriately set in the response object for the content the
servlet is
generating. The HTTP 1.1 specification does not require that this header be
set in
an HTTP response. Servlet containers must not set a default content type
when the
servlet programmer does not set the type.