I assume you're talking about using a Java JSR-109-compliant deployment descriptor to set the character set. As far as I'm aware, all products default to UTF-8, so you should only need to set the character set if you need to override this default.
Unfortunately, the JSR-109 specification does not define an attribute for setting the character set, therefore the mechanism used to set it will vary depending on the specific product you're using. For example, WebLogic 8 provides a deployment descriptor attribute called charset. See http://e-docs.bea.com/wls/docs81/webserv/i18n.html.
On the other hand, WebSphere 6 doesn't provide a means to set the character set via the deployment descriptor. Instead it must be set either in your client code or via a handler. See http://publib.boulder.ibm.com/infocenter/wasinfo/v6r0/index.jsp?topic=/com.ibm.websphere.express.doc/info/exp/ae/twbs_changeutf.html.
I suggest you submit your question to your vendor's discussion list.
This was first published in October 2005