How could I detect the bean is in session scope? What I am trying to do is this: In a jsp page, if the bean is in session scope, I will call beans method and get its values. If the bean is not in scope, I will direct the page to a servlet, which will instantiate a new bean and place it into the session.

You will need to have a simple scriptlet within your page to take care of this:

<% 
  MyBean beany = (MyBean) session.getValue("beanId");
  if (beany != null) {
%>
<jsp:getProperty name="beany" property="someProperty"/>
<jsp:getProperty name="beany" property="anotherProperty"/>
<% } else {
%>
<jsp:forward page="/servlet/myServlet"/>
<% } 
%>