Christopher Schultz wrote:
> > First of all, why is this so? > > This is likely because of the way you use the singleton. When you > have a "singleton" (I use quotes because it's probably not a real > singleton.... otherwise we would not be having this discussion) the > static data is associated with the java.lang.Class object that gets > created when your class is loaded. When the re-load occurs, that > static data sticks around. The new classloader used for the new > context loads a new copy of the "singleton" and they pile up over > time. You need to shutdown the connection pool before the context > dies.
I understand it sticks around because the data is independent of the any object. But eventually even this static data should get garbage collected.
Well, if this is not a GoF-Singleton what is it then...?
It's a Singleton only for the (temporary) ClassLoader in which it was created. In other words, it's not a "real" Singleton because multiple copies can exist in a given JVM.
public class ConnectionFactory { private static Logger logger = Logger.getLogger("ConnectionFactory"); private static ConnectionFactory instance; //stores references to all connection managers (connection pools) private final Hashtable managers = new Hashtable();
private ConnectionFactory() { //foo } public static ConnectionFactory getInstance() { if (null == instance) { instance = new ConnectionFactory(); } return instance; } }
> > Second of all, how can I prevent this? Somehow listen for reloads > > and react appropriately? > > Yes. Consider writing a ServletContextListener and "closing" the pool > before the context goes down. It will be run when the new context > comes up, too. > > Check the documentation for javax.servlet.ServletContextListener
I've just gone through its description. Looks my friend for this problem.
ServletContextListener is the standard way to address problems such as this. You alluded to possibly moving your ConnectionFactory.class to Tomcat's lib (or similar) directory to make it available to all webapps -- this isn't necessarily a bad idea, depending on what you want to accomplish, but it is an "advanced" configuration and you should fully understand the ClassLoading system before getting involved in it.
justin
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