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In this program, the event handlers call the getName method on the event objects to display information about the events on the client screen when the events occur. This is shown in Figure 1 and Figure 4 . Several other methods are available to be called on the event object including:

  • getName
  • getSession
  • getValue
  • getSource

An overridden toString method

In addition to the two event handler methods, the MyClass class also overrides the toString method. Note that the string returned by the overridden toString method is displayed in Figure 1 through Figure 3 to represent the MyClass object that is contained in the session object.

Event handler behavior

My objective was to display the name returned by the getName method on the browser screen for each event as shown by the third line in Figure 1 and the third line in Figure 4 . In order to accomplish this, the code in the event handler methods need accessto the output stream object. This was accomplished by

  • passing a reference to the output stream object to the MyClass constructor
  • saving that reference in an instance variable of the MyClass object
  • using that reference inside the event handler methods to send content to the browser

Standard source-listener event handling

Except for the fact that there is no requirement to register the event listener object on a source, this is straightforward source-listener eventhandling material that you should already be familiar with.

The code in Listing 9 also signals the end of the class named Java4590a .

Run the program

I encourage you to copy the code from Listing 10 . Compile the code and deploy it on your server. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Java4580: Session Tracking using the Session Tracking API
  • File: Java4580.htm
  • Published: 12/30/13
  • Revised: 02/07/16

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

Complete program listing

Listing 10 - The servlet named Java4580a.java.

/*File Java4580a.java, Copyright 1999, R.G.Baldwin Revised 12/30/13This servlet illustrates use of the session tracking API. A variety of different aspects of session tracking usingthe API are illustrated. ***************************************************************/import java.io.*; import java.util.*;import javax.servlet.*; import javax.servlet.http.*;public class Java4580a extends HttpServlet{public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException{//Get the session associated with this request, HttpSession session = request.getSession(true);response.setContentType("text/html");//Get the output stream from the session object. // If this is the first call to servlet, create an output// stream and save it in the session object. PrintWriter out = (PrintWriter)session.getValue("out");if(out == null){ //First request from this clientout = response.getWriter(); session.putValue("out",out);}//end if//Create HTML page header out.println("<html>"); out.println("<head><title>Java4580a</title></head>"); out.println("<body>");//Create a hit counter for this servlet Integer cnt = (Integer)session.getValue("counter");if(cnt == null) cnt = new Integer(1); else cnt = new Integer(cnt.intValue() + 1);session.putValue("counter",cnt);//Add a new Date object each time the servlet i called Date theDate = new Date();long millis = theDate.getTime(); String strMillis = "" + millis;session.putValue(strMillis,theDate);//When the hit counter is 1, instantiate a new object of // type MyClass and put it in the session. Pass // a reference to the output stream to the constructor.//Remove the object from the session when the value // of the hit counter is 4.if(cnt.intValue() == 1) session.putValue("MyClassObj", new MyClass(out));if(cnt.intValue() == 4) session.removeValue("MyClassObj"); //Display information about the session.out.println("<p>Session Characteristics:<br/>"); out.println("New Session: " + session.isNew()+ "<br/>"); out.println("Session ID: " + session.getId()+ "<br/>"); out.println("Session Context: "+ session.getSessionContext()+ "<br/>"); out.println("Creation Time: "+ new Date(session.getCreationTime()) + "<br/>"); out.println("Last Accessed: "+ new Date(session.getLastAccessedTime()) + "</p>"); //Display information about all of the objects currently in// the session. Note that the session now contains a // PrintWriter object that was not in the session in the// original version of the servlet named Java4580a. out.println("<p>Session Data:<br/>"); String[]names = session.getValueNames(); for(int i = 0; i<names.length; i++){ out.println(names[i]+ ": " + session.getValue(names[i]) + "<br/>"); }//end for loop//Finish off the HTML page out.println("</p></body></html>"); }//end doGet()//==========================================================////This is an inner class. In the original version, this class MyClass implements HttpSessionBindingListener,Serializable{ PrintWriter localOut;//local copy of output stream to clientpublic MyClass(PrintWriter out){//constructor//Save a local copy of the output stream to the client. localOut = out;}//end constructor public String toString(){return "This is a MyClass object"; }//end toString()//This method is called when the object is put into// the session. public void valueBound(HttpSessionBindingEvent e){localOut.println("<p>Event<br/>"); localOut.println("In valueBound method<br/>"); //Returns the name of the object as identified when// put into the session localOut.println("Name = " +e.getName() + "</p>"); }//end valueBound()//This method is called when the object is removed // from the session.public void valueUnbound(HttpSessionBindingEvent e){ localOut.println("<p>Event<br/>"); localOut.println("In valueUnbound method<br/>"); localOut.println("Name = " +e.getName() + "</p>"); }//end valueUnbound()}//end inner class named MyClass}//end class Java4580a


Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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