title: Check if session exists JSF
body: <p>I have a login page where I have a User bean to authenticate username and password for a person. This Bean is Session Scoped.
  If someone writes a URL and tries to jump the login page, how can I check that and redirect him to the login page?</p>
  
  <p>On the other hand. Suppose I have logged in and I was working and suddenly I go out for a while and my session expires. When I return and try to interact with the form it sends a message alerting me the session expiration. How can I redirecto again to the login form when this occurs?</p>
  
  <p>Thanks in advance. Hope I explain myself.</p>
  
  <p>Mojarra 2.1.4, Tomcat 7, Tomahawk 1.1.11</p>