<< Chapter < Page Chapter >> Page >

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

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 to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?