title: Gracefully handle expired HttpSession in Spring WebFlow
body: <p>(From <a href="http://forum.springsource.org/showthread.php?108833-Handling-expired-session-gracefully" rel="noreferrer">SpringSource forum</a>.)</p>
  
  <p>When the <code>HttpSession</code> has expired and the user re-submits a page in the flow, he/she is sent back to the beginning of the flow. All I want to add to this behavior is a message explaining why it occurred. "You were inactive, so you have been restarted..."</p>
  
  <p>What's the easiest/best-practice way to do this?</p>