Unfortunately, you can't. Once the HTML for A.jsp is written, it is set to the client. When the client (the browser) parses the HTML and sees that it contains a frame, it makes a subsequent request to the server. It is this request that is for B.jsp. Since it is a completely different request. There are a couple of solutions:
1. Place what ever stateful data you need in the session instead of the request.
2. Don't use frames. Instead, consider tables and JSP includes. For more on this, see the FAQ Why do Frames suck?