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


JSP displaying new and old name of the company


Session Related Listener

For all Sessions

ServletContextListener


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

Education

ashishsingh bhatia1prof

pages servlet jsp

servlet page

new session

web life cycle events

session related listener

jsp fileprof

case study