Is it necessary to make <listener-class> tag entry in web.xml even after adding @WebListener annotation to my listener class?

Question

Is it necessary to make listener-class tag entry in web.xml even after adding @WebListener annotation to my listener class?

Because when I use just @WebListener annotation without making listener-class tag entry in web.xml, my listener class does not get executed.

When I use both the listener-class tag entry in web.xml and @WebListener for my listener class, then only my listener class is getting executed.

(Additional info: java version "1.7.0_79" , Java(TM) SE Runtime Environment (build 1.7.0_79-b15)

Following is the listener-class tag entry in web.xml :

<listener>
        <listener-class>  org.shan.jspservlets.CountUserListener </listener-class>
</listener>

Following is my listener class :

package org.shan.jspservlets;

import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

@WebListener
public class CountUserListener implements HttpSessionListener {
	ServletContext ctx = null;
	static int total = 0, current = 0;

	public void sessionCreated(HttpSessionEvent e) {
		total++;
		current++;

		ctx = e.getSession().getServletContext();
		ctx.setAttribute("totalusers", total);
		ctx.setAttribute("currentusers", current);

	}

	public void sessionDestroyed(HttpSessionEvent e) {
		current--;
		ctx.setAttribute("currentusers", current);
	}

}

Answer 1

Annotations like @WebServlet, @WebListener, etc. were introduced in Servlet 3.0, so if you are using a servlet container with a servlet version < 3.0 the annotations are not processed.

Annotations are also not processed if the web-app element tells the container to ignore them:

<web-app metadata-complete="true" ...>

Then your annotated class must be either in WEB-INF/classesor in a jar in WEB-INF/lib, else the annotation is also ignored.