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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

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
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Do somebody tell me a best nano engineering book for beginners?
s. Reply
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Devang Reply
are you nano engineer ?
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Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
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?
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for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
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what is biological synthesis of nanoparticles
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what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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I'm interested in nanotube
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what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
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how did you get the value of 2000N.What calculations are needed to arrive at it
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