> > 1) What is a singleton? Is it one instance per classloader, one
> per JVM or
> > one per a cluster of machines?
>
> once per classloader. If you want to go beyond that you need another
> mechanism (it's just not possible within Java otherwise, as you need
> "static").
>
> > 2) This is similar to the root component manager issue (Berin
> > brought up the
> > fact that there are some security risks involved and that JNDI would be
> > safer), and I think a solution within that framework would be better. It
> > would also answer the first question.
>
> JNDI should be optional, methinks. So a JNDI-stored single-instance-only-
> objects-framework should be only ever an optional part.
Then the following is possible:
Per CL:
Component implements ThreadSafe and passes all messages on to a private
static final instance:
public class CLSingleton implements ThreadSafe {
private static final CLSingletonService instance = new CLSingletonService
();
public void doStuff() {
instance.doStuff();
}
}
Per Cluster:
Component is poolable and looks up the remote object in initialize() and
recycle():
public class ClusterSingleton implements Poolable, Recyclable,
Initializable, Disposable {
private ClusterSingletonService instance = null;
public void doStuff() {
instance.doStuff();
}
public void initialize () {
instance = doJNDILookup ();
}
public void dispose () {
disposeInstance ();
}
public void recycle () {
// To avoid memory leaks via RMI, dispose and lookup the JNDI instance.
}
}
So both types of singletons are possible without a new Singleton interface.
/LS
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