title: How to find session variable present or not
body: <p>How I can find values is set to variable in session or not?</p>
  
  <pre><code>if(session.getAttribute("tot_demand"))//need to change
  
    //if value is already set then do this.
  
  else
  
    //if not set then do this.
  </code></pre>
  
  <p>What do I need to write, for the above code to work?</p>