title: Practical Usage of HttpSessionBindingListener And HttpSessionAttributeListener
body: <p>I am reading through head first JSP and servlets. Going through different type of listeners, I came across <code>HttpSessionBindingListener</code> and <code>HttpSessionAttributeListener</code>. </p>
  
  <p>I was thinking about the difference between the two - I want to see the practical usages in real world examples of those two listeners. I tested <code>HttpSessionBindingListener</code> by implementing <code>valueBound()</code> and <code>valueUnBound()</code> - why would an object need to know whether it has been added or not?</p>
  
  <p>I am pretty confused about the practical usages. Please help in clarifying this.</p>