Ron,
Your approach works fine if your singletons are read only. I see a lot of
this for serving up static "reference data". The static singleton in your
case is a per VM "flyweight server".
We often have cases where a customer needs a true singelton service (e.g.
UUID generation) and having multitple static singletons doesn't work. In the
example of UUID, you need to keep a counter in the singleton, and having
multiple instance could give you UUID generation collisions.
Depends what you are trying to do...
Regards,
Chris.
> -----Original Message-----
> From: Ron Yust [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, October 27, 1999 9:32 AM
> To: [EMAIL PROTECTED]
> Subject: Re: Singletons (offshoot of EJB Restrictions-- threads, io)
>
> Chris,
>
> I don't agree. I currently use an architecture where we have a cluster
> pool
> of RMI servers that our clients connect to. Although they do not need to
> communicate between themselves, they do individually use static
> methods/data
> for all the objects they instantiated. We are a candidate for EJB if just
> to replace our load balancing architecture.
>
> Why do you believe that individual EJB servers couldn't benefit from
> static
> methods/data?
>
> -Ron
>
> > -----Original Message-----
> > From: A mailing list for Enterprise JavaBeans development
> > [mailto:[EMAIL PROTECTED]]On Behalf Of Chris Raber
> > Sent: Tuesday, October 26, 1999 5:44 PM
> > To: [EMAIL PROTECTED]
> > Subject: Re: Singletons (offshoot of EJB Restrictions-- threads, io)
> >
> >
> > What you should consider is that statics depend on class loader
> semantics
> > which are not appropriate for distrbuted architectures that EJB
> > is intented
> > to serve. If you only need a single server JVM for your server
> > objects, you
> > probably aren't a candidate for EJB anyway!
> >
> > -Chris.
> >
> >
> > > -----Original Message-----
> > > From: Ron Yust [SMTP:[EMAIL PROTECTED]]
> > > Sent: Tuesday, October 26, 1999 5:53 PM
> > > To: [EMAIL PROTECTED]
> > > Subject: Re: Singletons (offshoot of EJB Restrictions--
> > threads, io)
> > >
> > > You mean in order to use the equivalent of simple static global
> > variables
> > > I
> > > have to create an entity bean or use Corba and JNDI? Crazy! The more
> I
> > > get
> > > into EJB, the more the dream fades and a nightmare begins.
> > >
> > > > -----Original Message-----
> > > > From: A mailing list for Enterprise JavaBeans development
> > > > [mailto:[EMAIL PROTECTED]]On Behalf Of James Cook
> > > > Sent: Tuesday, October 26, 1999 3:40 PM
> > > > To: [EMAIL PROTECTED]
> > > > Subject: Singletons (offshoot of EJB Restrictions-- threads, io)
> > > >
> > > >
> > > > Theory
> > > > ==========
> > > > You can achieve "singletons" in EJB by using a BMP entity bean.
> > > > Override the
> > > > findByPrimaryKey object to always return the same primary key
> > > > value. Do not
> > > > provide a create method.
> > > >
> > > > Caveat
> > > > ======
> > > > 1. An EJB container is not required to create a single instance
> > > > of an entity
> > > > bean per container. Many of the more scalable implementations will
> not
> > > do
> > > > this. They rely on the underlying database to provide
> synchronization
> > > > through isolation levels. Even if the container *does*
> > > > synchronize access to
> > > > a single instance of the entity bean, multiple containers housing
> the
> > > same
> > > > bean will create multiple instances. Therefore, this does not
> > result in
> > > a
> > > > *true* singleton object, although it may be suitable for your needs.
> > > >
> > > > 2. The transaction overhead usually associated with entity
> > beans is not
> > > > often desirable.
> > > >
> > > > Solution
> > > > ========
> > > > Don't use EJB to implement singletons. I would create a remote
> > > > CORBA object
> > > > and bind it in the JNDI namespace. Sure, I end up implementing my
> own
> > > > lifecycle management (or my CORBA container does), but we've been
> > > > doing that
> > > > for years before anyone heard of EJB.
> > > >
> > > > jim
> > > >
> > > > ----- Original Message -----
> > > > From: Ara Abrahamian <[EMAIL PROTECTED]>
> > > > To: <[EMAIL PROTECTED]>
> > > > Sent: Thursday, September 23, 1999 1:50 PM
> > > > Subject: Re: EJB Restrictions-- threads, io
> > > >
> > > >
> > > > > As far as I know only entity beans and JNDI contents are shared,
> > > > > session beans don't. But entities are persistent. Suppose I want
> > > > > to have something like a "static activeUsersList" in a bean and
> act
> > > > > as a true singleton object, only one instance avialable.
> > > > > How can I "cleanly" implement it?
> > > > >
> > > > > Ara Abrahamian
> > > > > bi!
> > > >
> > > > ==================================================================
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> > > >
> > > >
> > >
> > >
> >
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