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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:
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
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 .
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.
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.
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-
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