Servlet Event framework

APPLICATION EVENT FRAMEWORK
Prof. AshishSingh Bhatia
1Prof. AshishSingh Bhatia

What and Why ?
 Life cycle methods
 How to respond to major events in the life cycle of the web application
?
 Who will do what ?
 Eight kind of listeners that respond to web life cycle events.
Prof. AshishSingh Bhatia 2

Listeners Interface
 ServletContextListener
 ServletContext AttributeListener
 HttpSessionListener
 HttpSessionAttributeListener
 HttpSessionActivationListener
 HttpSessionBindingListener
 ServletRequest Listener [ 2.4 ]
 ServletRequestAttributeListener [ 2.4 ]

How ?
 Implement the appropriate interface.
 Implement the methods needed to respond to the events of interest.
 Obtain access to the important Web application objects.
 Use these objects.
 Declare the listener.
 Provide any needed initialization parameters.

Take a Case Study and Think out of Box
 We are enterprise level [ Huge Company with lot many pages of web
application ]
 Where company whose name changes frequently
 We need to display company name in all pages [ Servlet / JSP ]
 How we can do that ?

Take a Case Study and Think out of Box
 As it is needed in application wide we will put it in web.xml as context-param
<context-param>
<param-name>companyName</param-name>
<param-value>test.com</param-value>
</context-param>
 In Servlet we will read it using
String name = getServletContext().getInitParameter(“companyName”);
Guess we have 100 [ Servlet / JSP ]
If we forgot to add entry in web.xml ?
Every Servlet / Page will display null
!!!!

Monitoring creation and destruction of Servlet Context

web.xml

JSP File

Take a new case
What if servlet change
the companyName of
context-param ?
Example : asbspace.in

Take a new case
We should ensure that when company
name is changed
formerCompanyName should also be
changed
companyName = asbspace.in
formerCompanyName=test.com
ServletContextAttributeListener

HTML Form

Servlet Changing Name

ServletContextAttributeListener

JSP displaying new and old name of the company

Session Related Listener
 For all Sessions
 ServletContextListener
 ServletContextAttributeListener
 For Specific Sessions
 HttpSessionListener
 HttpSessionAttributeListener
 Counting number of sessions
 HttpSessionListener Interface : sessionCreated and sessionDestroyed

test.jsp
makesession.html

sessioncount.jsp

Cookies must be disabled. So each
jsp load will act as a request and
create a new session

sessioncount.jsp output

Watching for changes in Session Attribute
 HttpSessionAttributeListener interface. Implement attributeAdded,
attributeReplaced, and attributeRemoved
 It gets notified when an object is placed into the session scope for the
first time, replaced by another object, or removed from the session
scope altogether.

Task – Self Study
 Suppose you want to track buying patterns for a specific item (a yacht, in
this case). Of course, you could try to find all servlets and JSP pages that
process orders and change each one to record yacht purchases. That’s an
awful lot of work for what sounds like a simple request, though, and pretty
hard to maintain, anyhow. A much better option is to create a session
attribute listener that monitors the attributes corresponding to order
reservations or purchases and that records the information in the log file for
later perusal by the sales manager.

Calculating Server Request Load

END OF SESSION
25Prof. AshishSingh Bhatia

Servlet Event framework

More Related Content

Similar to Servlet Event framework (20)

More from AshishSingh Bhatia (6)

Recently uploaded (20)

Servlet Event framework