If you really want to do this, just specify redirect="true" when you define the forward to b.jsp in the struts-config.xml file.
However, there are some really good reasons for not doing this. The first one is that if you do this, anything you put in the request object will be lost. Anything you want passed on to the JSP will have to be either passed as a parameter in the URL, or put in the session. The second one is... well, here's an example:
Suppose that abc.do retrieves data from the database before displaying b.jsp, and that if you try to display b.jsp without hitting the abc action first, the page will throw exceptions. Then suppose the user bookmarks the page with the url of http://localhost:8080/testing/b.jsp. What's going to happen? You got it... exceptions.