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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