Tomcat Redirect based on Cookie Value

I'm a little new to this.

What I want to do: Under Tomcat I want to check if a "开发者_开发知识库user_name" cookie exists within a webapp. If it does not I want to redirect to another site to set the cookie (same domain) and then redirect back to the requested page.

The service that I'm using to set the user_name cookie works fine, I just need to understand whether I can check for the cookie and redirect to that page if the cookie doesn't exist within my Tomcat config or if this check/redirect has to happen in the code for the webapp.

So:

If cookie user_name exists 
     run webapp
else 
     redirect to https://ServerToSetUser_id?http://myhost/userrequestedpath/

This is easy, and is not specific to Tomcat. It is part of the servlet spec, so works in any container. Your servlet/JSP has access to a request object of type HttpServletRequest.

Call getCookies() and iterate through the Cookies it returns to look for the one you want. If you find it, continue. If you don't, use sendRedirect("http://otherserver.com") on HttpServletResponse to send your redirect and then finish your servlet/JSP processing.