When HttpSessionAttributeListener and HttpSessionBindingListener methods are called?

Hi Friend,

I am trying to understand usage of the listeners. But I am kind of stuck in at usage of the HttpSessionAttributeListener and HttpSessionBindingListener. I have written a ServletContextListener:

To set the Dog context object which implements HttpSessionAttributeListener & HttpSessionBindingListener:

package home.example.httpsessionbindinglistener;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

public class Dog implements HttpSessionAttributeListener, HttpSessionBindingListener {
	private String breed;
	Dog(String breed) {
		System.out.println("Dog.Dog(): " + this.hashCode());
		this.breed = breed;
	}
	public String getBreed() {
		return breed;
	}
	@Override
	public void attributeAdded(HttpSessionBindingEvent event) {
		System.out.println("Dog.attributeAdded(): " + this.hashCode());
	}
	@Override
	public void attributeRemoved(HttpSessionBindingEvent event) {
		System.out.println("Dog.attributeRemoved(): " + this.hashCode());
	}
	@Override
	public void attributeReplaced(HttpSessionBindingEvent event) {
		System.out.println("Dog.attributeReplaced(): " + this.hashCode());
	}
	@Override
	public void valueBound(HttpSessionBindingEvent arg0) {
		System.out.println("Dog.valueBound(): " + this.hashCode());
	}
	@Override
	public void valueUnbound(HttpSessionBindingEvent arg0) {
		System.out.println("Dog.valueUnbound(): " + this.hashCode());
	}
}

And written a Servlet which gets the Dog object and prints.

As you can see here I also overwrite, remove and re-assign the Dog object but I don't see any trace!!!

I can only see the Constructor calls

...

my web.xml is:

This is the example given in the Head First Servlet & JSP 2nd Edition (Page 183)!!!

Can you please let me know, what should I need to do to trigger those methods??

Thanks,
Krishna

Here's a little hint: You're using a HttpSessionAttributeListener and a HttpSessionBindingListener. Maybe the servlet API contains some other class that is better suited for handling context attributes?

Ulf Dittmer wrote:Maybe the servlet API contains some other class that is better suited for handling context attributes?

I am using the Apache Tomcat 6.0, are you aware of any other attribute handler here?? Still I think it should be supported as per Java Servlet Spec.

Please let me also know if I am using these interfaces wrongly??

Thanks,
Krishna

Krishna D. Bhat wrote:Still I think it should be supported as per Java Servlet Spec

How so? Where in the Servlet spec does it say that session listeners will be called when you are doing nothing that has anything at all to do with sessions?

Krishna D. Bhat wrote:I am using the Apache Tomcat 6.0, are you aware of any other attribute handler here?? Still I think it should be supported as per Java Servlet Spec.

Please let me also know if I am using these interfaces wrongly??

Thanks,
Krishna

Krishna,

Please read again Ulf's post. He was giving you a really big hint. Look at the parts of the message he emboldened

Bear Bibeault wrote:How so? Where in the Servlet spec does it say that session listeners will be called when you are doing nothing that has anything at all to do with sessions?

Hmmm Yes!!!

now I got it!!!

I was confused the Session attribute listeners to work when attribute in the Context is changed.

Thanks Bear Bibeault!!! I will try doing in the HttpSession.

Thanks,
Krishna