The best way I know to do this would be to change the link so that it calls a javascript function using the onclick event, or changing the link to "javascript:myfunction()". In that function put code that changes the action of the form and submits it. A link does not preserve the state of the form before loading another page, while a form submission does.
So, you might create a new action mapping that simply forwards to page B. Then, in your javascript function, change the form's action property to the new action mapping and submit the form.
Struts will then populate your form bean with whatever the user entered before clicking the link. If the user goes back to Page A, the fields will be populated.
