ServletContext AttributeListener again

Hi again, can anyone explain why the code below doesn't execute the
attributeAdded(...) method

package pack1;
 
import java.io.*;
import java.net.*;
 
import javax.servlet.*;
import javax.servlet.http.*;

public class ShowFrame extends HttpServlet implements ServletContextAttributeListener
{
       protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException
    {
        this.getServletContext().setAttribute("name","cat");
        String v=(String)this.getServletContext().getAttribute("name");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        // TODO output your page here
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet ShowFrame</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>V = "+v+"</h1>");
        out.println("</body>");
        out.println("</html>");
         
        out.close();
    }
 
    public void attributeAdded(ServletContextAttributeEvent scab)
    {
        this.getServletContext().setAttribute("name","chicken");
    }
 
    public void attributeRemoved(ServletContextAttributeEvent scab)
    {
        this.getServletContext().setAttribute("name","chicken");
    }
 
    public void attributeReplaced(ServletContextAttributeEvent scab)
    {
        this.getServletContext().setAttribute("name","chicken");
    }
}

The servlet is included in the web.xml file under <listener> tag.
Thanks for any help

Please keep the discussion in your original topic.