Stateful Session Bean Undestanding - Ivan's note

[Shankar sanjay]

Hi,

My understanding is Stateful session bean has to maintain state for each client. I got an example from Ivan's tutorial 2.Create a Stateful Session Bean (http://www.slideshare.net/krizsan/ocp-jbcd-6-study-notes) page # 22.

1. I opened the following URL in IE, (its first request, so new Stateful Session Bean has to create)
http://localhost:8080/StatefulSession1Web/test.do?name=Ivan

2. I opened the following URL using Chrome (its second request, so new StatefulSession bean has to create).

http://localhost:8080/StatefulSession1Web/test.do?name=second

But seems only one stateful session been has been created. Can anyone please clarify me?

I am not sure anybody has tried that.

[Frits Walraven]

Hi Shankar,

But seems only one stateful session been has been created. Can anyone please clarify me?

What gives you the idea that there is only one created? Can you post the code of your Session bean?

Regards,
Frits

[Shankar sanjay]

package com.ivan.scbcd6;

import java.util.Date;
import java.util.concurrent.TimeUnit;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.ejb.LocalBean;
import javax.ejb.Remove;
import javax.ejb.Stateful;
import javax.ejb.StatefulTimeout;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;

/**
 * Simplest possible stateful session bean exposing a local, no-interface view.
 */
@Stateful
@LocalBean
@StatefulTimeout(value = 10, unit = TimeUnit.SECONDS)
@TransactionAttribute(TransactionAttributeType.NEVER)
public class StatefulSession1Bean {
	private static int sCurrentInstanceNumber = 1;
	private int mInstanceNumber;

	@PostConstruct
	public void initialize() {
		mInstanceNumber = sCurrentInstanceNumber++;
		System.out.println("*** StatefulSession1Bean " + mInstanceNumber
				+ " created.");
	}

	@PreDestroy
	public void destroy() {
		System.out.println("*** StatefulSession1Bean " + mInstanceNumber
				+ " destroyed.");
	}

	@Remove
	public void remove() {
		System.out.println("*** StatefulSession1Bean " + mInstanceNumber
				+ " remove.");
	}

	/**
	 * Creates a greeting to the person with the supplied name.
	 * 
	 * @param inName
	 *            Name of person to greet.
	 * @return Greeting.
	 */
	public String greeting(final String inName) {
		Date theCurrentTime = new Date();
		String theMessage = "Hello " + inName + ", I am stateful session bean "
				+ mInstanceNumber + ". The time is now: " + theCurrentTime;
		return theMessage;
	}
}
 

[Frits Walraven]

and what shows your console?

[Shankar sanjay]

INFO: *** StatefulSession1Bean 1 created.
INFO: *** StatefulSession1Bean 1 remove.
INFO: *** StatefulSession1Bean 1 destroyed.

My question was..

1. I opened the following URL in IE, (its first request, so new Stateful Session Bean has to create)
http://localhost:8080/StatefulSession1Web/test.do?name=Ivan

2. I opened the following URL using Chrome (its second request, so new (2nd) StatefulSession bean has to create).

http://localhost:8080/StatefulSession1Web/test.do?name=second

[Frits Walraven]

Did you open the URL in Chrome within 10 seconds (before the first Session bean gets destroyed)?

[Shankar sanjay]

Yes tried in 10 secs only. otherwise i would have got NosuchEJBException, Later i tried with 300 Seconds too :-), but output same

[Frits Walraven]

Ok, I have looked at the setup in Ivan notes and I have noticed that there is a serious mistake in his example.

There is only one Servlet responding to all the requests, and in that Servlet the EJB is injected once (i.e. for every client the same Stateful Session Bean). There will never be a second bean.

The way to implement this example is to add a HTTPSessionListener and do a lookup for an Stateful EJB and store in in the Session.

Add this listener to your code:

package com.ivan.scbcd6.client;

import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

import com.ivan.scbcd6.StatefulSession1Bean;

public class SessionEJBListener implements HttpSessionListener {

	@Override
	public void sessionCreated(HttpSessionEvent arg0) {
		InitialContext context;
		try {
			context = new InitialContext();
			StatefulSession1Bean bean = (StatefulSession1Bean)context.lookup("java:global/StatefulSession1Web/StatefulSession1Bean");
			arg0.getSession().setAttribute("statefulBean", bean);
			System.out.println("sessionCreated");		
		} catch (NamingException e) {
	
			e.printStackTrace();
		}
	}
	@Override
	public void sessionDestroyed(HttpSessionEvent se) {
		// not implemented

	}

}

and add this to your web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
  <display-name>StatefulSession1Web</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <listener>
    <listener-class>com.ivan.scbcd6.client.SessionEJBListener</listener-class>
  </listener>
</web-app>

and do this in your Servlet:

package com.ivan.scbcd6.client;

import java.io.IOException;
import java.io.PrintWriter;
import javax.annotation.PostConstruct;
import javax.ejb.EJB;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.ivan.scbcd6.StatefulSession1Bean;

/**
 * Servlet implementing a local EJB client.
 * 
 * @author Ivan A Krizsan
 */
@WebServlet(name = "StatefulSession1Servlet", urlPatterns = "/test.do")
public class StatefulSession1Servlet extends HttpServlet {
	/* Constant(s): */
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	@Override
	protected void doGet(HttpServletRequest inRequest,
			HttpServletResponse inResponse) throws ServletException,
			IOException {
		PrintWriter theResponseWriter = inResponse.getWriter();
		String theRequestNameParam = inRequest.getParameter("name");
		if (theRequestNameParam == null) {
			theRequestNameParam = "Anonymous Coward";
		}
		StatefulSession1Bean mStatefulSessionBean = (StatefulSession1Bean) inRequest.getSession().getAttribute("statefulBean");
		String theResponse = mStatefulSessionBean.greeting(theRequestNameParam);
		theResponseWriter.println("Response from the EJB: " + theResponse);
	}
}

When you run the example now, you will see what you had expected:

INFO: *** StatefulSession1Bean 1 created.
INFO: sessionCreated

INFO: *** StatefulSession1Bean 2 created.
INFO: sessionCreated

INFO: *** StatefulSession1Bean 3 created.
INFO: sessionCreated

INFO: *** StatefulSession1Bean 1 destroyed.

INFO: *** StatefulSession1Bean 3 destroyed.
INFO: *** StatefulSession1Bean 2 destroyed.

Regards,
Frits

[Ivan Krizsan]

Hi!
Thanks for pointing this out!
I will update the notes as soon as I am able to.
Best wishes,
Ivan

[Shankar sanjay]

Good catch Frits! thanks a lot.. it works as expected. thanks again :-)

[Ivan Krizsan]

Hi!
Finally, a new version of the book is available.
The above mentioned example has been corrected, as well as a number of other mistakes and typing errors I made.
Best wishes!

[gurpeet singh]

for every request a new thread will be generated that will run the service() method. ain't different threads will be treated as separate clients ? or will they be treated as request coming from the same client ?.

[Prajakta Acharya]

As per my understanding, following scenarios will be treated equally by the server.
1) Different requests from same client to the same servlet or
2) Different requests from different clients to same servlet,

Servlet's service() method will be executed in threads for both these scenarios.

Whether a new bean gets created or not, depends on the location of look-up code. If look-up is done in the doGet() or doPost() method, then every look-up of stateful bean should return a new instance.

We had a long discussion about this on this link :
https://coderanch.com/t/611980/java-EJB-SCBCD/certification/Comparing-stateful-session-bean-stateless