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Web Component Certification (OCEJWCD)

mistake in JavaDocs(JDK1.4) regarding Listeners

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posted 19 years ago

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I believe that I found a mistake in the JavaDocs. I was studying the API for the various listeners and comparing to the Servlet Specifications.
Servlet Specifications (SRV.10.2.1):
Has a table SRV.10-1 "Events and Listener Interfaces" and indicates 4 listeners =>
javax.servlet.ServletContextListener
javax.servlet.ServletContextAttributeListener
javax.servlet.http.HttpSessionListener
javax.servlet.http.HttpSessionAttributeListener
Specification (SRV.10.3.2)Deployment Descriptors says =>
Listener classes are declared in the web application deployment descriptor using the listener element. They are listed by class name in the order in which they are to be invoked.
JavaDocs for ServletContextListener ==>
... "To receive notification events, the implementation class must be configured in the deployment descriptor for the web application".
JavaDocs for ServletContextAttributeListener ==>
... "To receive notification events, the implementation class must be configured in the deployment descriptor for the web application".
JavaDocs for HttpSessionListener ==>
... "To receive notifcation events, the implementation class must be configured in the deployment descriptor for the web application".
JavaDocs for HtttpSessionAttributeListener ==>
... (nothing - this is an error of ommission)
What the JavaDocs for HttpSessionAttributeListener SHOULD SAY =>
... "To receive notifcation events, the implementation class must be configured in the deployment descriptor for the web application".
////////////////////////////////////
Do people here agree with me? How do I report a mistake in the JavaDocs?
thanks!
Kevin Thompson
[ July 31, 2002: Message edited by: Kevin Thompson ]

R K Singh

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posted 19 years ago

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submit a bug on sun site

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Kevin Thompson

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posted 19 years ago

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ok - I submitted it as a bug with Sun. If they get back to me about it, I will post the info here.
thanks
Kevin Thompson
P.S. And of course I made a mistake in the title of my original post here on JavaRanch.
The actual location of the error within the JavaDocs is =>
J2EE SDK 1.3.1 FCS
(Java Servlets 2.3)
[ July 31, 2002: Message edited by: Kevin Thompson ]

Yu Chen

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posted 19 years ago

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1. How would I declare/register other listeners, like HttpSessionActivitionListener or HttpSessionBindingListener? Is deployment descriptor the only way to register listeners?
2. What are differences between HttpSessionAttributesListeners and HttpSessionBindingListener? Both are listenering to the HttpSessionBindingEvent triggered by either setAttribute() or removeAttribute(), WHEN should I use WHICH?
Thanks in advance.
-yu chen

SCJP2 SCWCD

R K Singh

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posted 19 years ago

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Try this out ...
GUI for experiment

====================================
Servlet

package foryou.servlet;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import presentation.exa.sessionlistener.MySessionBindingListener;
public class MySessionServlet extends HttpServlet
{
  protected void service(HttpServletRequest request,
            HttpServletResponse response)
            throws IOException, ServletException
  {

response.setContentType("text/html");
 ServletOutputStream out = response.getOutputStream();
 MySessionBindingListener sessBindLis = new MySessionBindingListener();
 HttpSession session = request.getSession(true);
 out.print("<?xml version='1.0' encoding='UTF-8'?>");
 out.print("<!DOCTYPE html");
 out.print("PUBLIC '-//W3C//DTD XHTML 1.0 Strict//EN'");
 out.print("'DTD/xhtml1-strict.dtd'>");
 out.print("<html>");
 out.print("<head>");
 out.print("<title>Maintaining Session State</title>");
 out.print("</head>");
 out.print("<body>");
 out.print("<center>");
 String action = request.getParameter("action");
 Double balance = (Double) session.getAttribute("Balance");
 debug("bal is " + balance);
 if (balance == null)
 {
 balance = new Double(500);
 session.setAttribute("Balance", balance);
 out.print(balance.doubleValue());
 out.print(" ");
 } else {
 double bal = balance.doubleValue();
 debug("action :: " + action);
 if (action.equals("withdraw"))
 {
 bal -= 50;
 balance = new Double(bal);
 session.setAttribute("Balance", balance);
 } else if (action.equals("deposit"))
 {
 bal += 50;
 balance = new Double(bal);
 session.setAttribute("Balance", balance);
 } else if (action.equals("bound"))
 {
 session.setAttribute("bound",sessBindLis);
 } else if (action.equals("unbound"))
 {
 //session.invalidate();
 session.removeAttribute("bound");//,sessBindLis);
 }else if (action.equals("remove"))
 {
 //session.removeAttribute("Balance");
 session.setAttribute("Balance",null);
 }

// balance = new Double(bal);
// session.setAttribute("Balance", balance);
 out.print("Your new balance is: ");
 out.print(bal);
 out.print(" ");
 }

out.print("<a href='./sessionservlet?action=deposit'>");
 out.print("Deposit Rs.50");
 out.print("</a>");
 out.print(" ");
 out.print("<a href='./sessionservlet?action=withdraw'>");
 out.print("Withdraw Rs.50");
 out.print("</a>");
 out.print(" ");
 out.print("<a href='./sessionservlet?action=bound'>");
 out.print("bound an object");
 out.print("</a>");
 out.print(" ");
 out.print("<a href='./sessionservlet?action=unbound'>");
 out.print("unbound the object");
 out.print("</a>");
 out.print(" ");
 out.print(" ");
 out.print(" ");
 out.print("<a href='./sessionservlet?action=remove'>");
 out.print("put null in Bala");
 out.print("</a>");
 out.print(" doing set:session.setAttribute(\"Balance\",null); AND event is REMOVED");
 out.print("</center>");
 out.print("</body>");
 out.print("</html>");
 }
 private void debug(String str){
 // System.out.println(str);
 }
}

====================================
Listeners classes
================ HttpSessionBindingEvent =================

==================== HttpSessionAttributeListener, HttpSessionListener ===============

package foryou.exa.sessionlistener;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public final class MySessionListener
  implements HttpSessionAttributeListener, HttpSessionListener {

public void sessionCreated(HttpSessionEvent event) {
    System.out.println("\n*******> HttpSession object has been CREATED\n\n");
  }

public void sessionDestroyed(HttpSessionEvent event) {
    System.out.println("\n*******> HttpSession object has been REMOVED\n\n");
  }
  public void attributeAdded(HttpSessionBindingEvent event) {
    System.out.println("\n*******> An attribute has been ADDED " +
      "to an HttpSession object\nAttr Name :" + event.getName() );
  }
  public void attributeRemoved(HttpSessionBindingEvent event) {
    System.out.println("\n*******> An attribute has been REMOVED " +
      "to an HttpSession object\nAttr Name :" + event.getName() );
  }

public void attributeReplaced(HttpSessionBindingEvent event) {
    System.out.println("\n*******> An attribute has been REPLACED " +
      "to an HttpSession object\n\nAttr Name :" + event.getName() );
  }
}

compile and run it

"Thanks to Indian media who has over the period of time swiped out intellectual taste from mass Indian population." - Chetan Parekh

Jason Chaw

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posted 19 years ago

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hi, guys, I think the JavaDocs is all right.
Please refer to the comments by Roseanne Zhang
in Aleks Pascoal's "HttpSessionActivationListener" topic,
There are two listerner interfaces not needed to configuared in web.xml:
javax.servlet.http.HttpSessionBindingListener
javax.servlet.http.HttpSessionActivationListener

Sun Certified Web Component Developer for the J2EE Platform Sun Certified Programmer for the Java 2 Platform Oracle Certified Associate

Kevin Thompson

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posted 19 years ago

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There IS a mistake in the JavaDocs. I did read the post by Roseanne Zhang in Aleks Pascoal's "HttpSessionActivationListener" topic. That is why I found the error in the JavaDocs!
The JavaDocs has an error of ommission in the text for HttpSessionAttributeListener. (as I outlined in my original post here).
Roseanne Zhang was absolutely correct.
There are 4 listeners that require web application deployment descriptors as follows:
1. ServletContextListener (JavaDocs correct)
2. ServletContextAttributeListener (JavaDocs correct)
3. HttpSessionAttributeListener (has ERROR OF OMMISSION in JavaDocs)
4. HttpSessionListener (JavaDocs correct)
There are 2 listeners that do not require web application deployment descriptors as follows:
1. HttpSessionActivationListener (JavaDocs correct)
2. HttpSessionBindingListener (JavaDocs correct)
YU Chen: I don't know how to answer your questions.
Jason Chaw: I see you are certified as an "Oracle Certified Assistant". Do you have any links for that? I have not heard of that certification before? Could you give me some info? Thanks!
Kevin Thompson
[ August 03, 2002: Message edited by: Kevin Thompson ]

Jason Chaw

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posted 19 years ago

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Sorry, kevin, I made a wrong spelling: "Associate" to "Assistant", thought they are synonymous.
This is the first level certification of the Oracle DBA. Two exams needed: PL/SQL and Database Fundamentals I. I think OCA is enough for me as a developer. The tests helped me a lot to learn the basic knowledge of Oracle Database.
I also confuse about that two listener.

I was lucky to pass the exam. I will do some tests about it. see you.

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Yu Chen

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posted 19 years ago

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Thanks Ravish Kumar's codes, I did some experiments with a few cases:
Thompson is right, there is a omission in JavaDoc. HttpSessionActivionListener must be declared in web.xml. And HttpSessionBindinerListener does not.
So as you listed before, 4 listeners need to be declared, and two others does not.
Here comes another ?, is it ok to declare inner classes as listners in web.xml? For example, I put MySessionAttribute and MySessionListener inside HttpSessionServlet as inner classes, and declare them as follows:
<web-app>
<listener>
<listener-class>chapter4.MySessionServlet.MySessionListener</listener-class>
</listener>
<listener> <listener-class>chapter4.MySessionServlet.MySessionAttributeListener</listener-class>
</listener>
...
I got error status: 404. In the tomcat log files, it does have ClassNotFoundException.
Any explainatins, ideas??
-yu chen

SCJP2 SCWCD

Hema Menon

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Posts: 569

posted 19 years ago