Singleton implemented using Servlets

[jeff wisgo]

I am trying to create only a single instance of a class which will run once Jakarta-Tomcat begins execution. To do this I have the following code:

*web.xml*

  <servlet>
    <servlet-name>initializecontroller</servlet-name>
    <servlet-class>roverlook.InitializeController</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>      

*InitializeController.java*

public class InitializeController extends HttpServlet {
 
  public void init(ServletConfig config) throws ServletException {
    super.init(config);
    
    Daemon.INSTANCE.start(); // start daemon thread
  }
 
}

*Daemon.java*

public class Daemon extends Thread{
 
  public static final Daemon INSTANCE = new Daemon(null); // singleton
 
 
  public synchronized void run  () {
 
     while(true) {
  
        LoggerCentral.info("Daemon executing required jobs at "+ (new java.util.Date()).toString(), null);
 
        // do work here
 
        try {
   Thread.sleep(1000*60);        
        } catch (InterruptedException e) {
  LoggerCentral.exception("Daemon:run():sleep interrupted", null);
        }
      } 
    }    
 
 

When I run Jakarta-Tomcat, I can see the Daemon writing once every ~1 minute as expected. However, when I run other Servlets (which aren't related to this) there are additional instances of the Daemon which are apparently created, because I see many writes to the logfile, sometimes only 1 second apart. It seems like the init() function is being called again even though I t should not be.

Can anyone help out?

Thanks
[ October 01, 2004: Message edited by: jeff wisgo ]

[Bear Bibeault]

I do not know what is causing your problem, but you might want to look into using context listeners to perform single-shot startup/shutdown actions rather than servlets.

[jeff wisgo]

After doing some more research, it appears that the problem may be related to multiple class loaders, does anyone the semantics of how class loaders interact with Tomcat?