paypal jsp:
<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
    <!-- other stuff -->

    <input type="hidden" name="return" value="payment">
    <input type="hidden" name="cancel_return" value="http://localhost:8080/watchy/payment-method.jsp">
</form>

struts.xml:
<action name="payment" class="ph.watchy.action.PaymentAction">
    <result>/transaction-result.jsp</result>
</action>