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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.

Miscellaneous

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
Disclaimers:

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

-end-

Questions & Answers

current economic plans (MDGS) needs
Ajijola Reply
I don't know what is happening
surajkumar
What is economic
Joeali Reply
What is the importance of study economics
Wilma
Economic is the study of how humans make decisions in face of sacristy
Wilma
economics is the study of how humans makes decision in the face of scarcity
Kpienta
economics is the study of human behaviour when faced with difficult situation example when goods and services are scarcity.
Sydney
what is Economic
Dauda Reply
what is 4ps of economic?
thomas Reply
production place Price product
Benedict
Criticism of elasticity
Siddikur Reply
what is unemployment
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I need more explanation
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not working
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some one who is willing qualified to work but can't find job
jackie
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Abubakar
some one who is willing to work but can't find job
Hawa
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Hawa
unemployment refers to the ability for someone who is capable and willing to work but could not find a job..
Mnoko
some one who not able to find a job
Dennis
please what is the secret of learning?
thomas
What is stock market?
JOHN Reply
explain the various types of cost curve
Ruth Reply
Short-run average fixed cost (SRAFC) Short-run average total cost (SRAC or SRATC) Short-run average variable cost (AVC or SRAVC) Short-run fixed cost (FC or SRFC) Short-run marginal cost (SRMC) Short-run total cost (SRTC)
Romy
what's economic development and growth
Popoola Reply
what do you understand by Ceteris Paribus?
Gabriel Reply
the external factor will remained constant, except the price
Hasib
everything being equal
Chenwi
explain the uses of microeconomics
Nikita Reply
uses of microeconomics
Nikita
Adam Smith's definition of economics
Sylvia Reply
what is economic deficit
Amjad
this is a situation whereby a nation's outcome or available resources are not enough to the people thereby causing scarcity
Ariel
prices of Quality demanded is equal to Quality supplied
NABUBOLO Reply
it's quantity demand and quantity supplied that's called equilibrium
Romy
no
NABUBOLO
they deal With prices
NABUBOLO
define the elasticity
NABUBOLO
explain different types of elasticity
NABUBOLO
oops 😬 you are right you talk about quality I tell about quantity
Romy
elasticity is the measurement of the percentage change of one economic variable in response to a change in another
Romy
Cross Elasticity of Demand (XED) Income Elasticity of Demand (YED) Price Elasticity of Supply (PES)
Romy
anything else?
Romy
I need to know everything about theory of consumer behavior
Grace
Romy, what is microeconomic?
thomas
What is Economic please
Dauda
Thomas, microeconomics is the study of how consumers, workers, and firms interact to generate outcomes in specific markets
Kieran
Dauda, economics is the study of people and choices. it is on one side the study of wealth and on the more important side, a part of the study if man
Kieran
How does one analyze a market where both demand and supply shift?
Gabriel Reply
That's equilibrium market
Ramon
but an equlibrum can appear twice on the same market... both in Movement along the Demand/supply curve of shift in the Curve
Gabriel
I Mean on the same curve..
Gabriel
how can consumer surplus be calculated
Franklyn
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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
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