If you are forwarding to the JSP, attaching the reference to the request is an alternative to a session variable. See the JavaDocs for the javax.servlet.ServletRequest interface - setAttribute and getAttribute methods.
If on the other hand you are redirecting to the JSP, you can only use the session since a new request will be created.
[picky-mode] Typically you dont "pass" an object, you pass a reference to the object. Using the wrong terms leads to sloppy thinking[/picky-mode]