用HttpSessionListener监听器好象做不到，为什么？
package texts;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionEvent;
public class OnLineListener implements HttpSessionListener{
public OnLineListener() {
}

public void sessionCreated(HttpSessionEvent event)
{

event.getSession().setMaxInactiveInterval(-1);
System.out.println("Created");
}
public void sessionDestroyed(HttpSessionEvent event)
{
System.out.println("destroyd");

}
}