On Dec 7, 2009, at 3:33 AM, Mansour Al Akeel wrote:
Thank you all.
I am reading more about this. I have done some reading before asking
the question, as I am not expecting the work to be done for me.
However, just like any new EJB user, the concept was not fully
comprehended and there was some confusion.
I have used JPA before, but not with EJB (with spring container). I
realized later that a statefull session is attached and specific to
the session.
My requirements will fit with a stateless bean or an entity (but I
don't need a db), so it will be a stateless.
To make things clearer, I will explain quickly what I am doing. I need
to simulate the interaction for the some units in an organization
(Emergency response). The units (initially, police , ambulance, fire
fighters ), responds and acknowledge and communicate the info they
receive using messaging.
I thought EJB and JMS will fit especially with the distributed nature
of the system (servers represents federates, where units can be
borrowed ). I was looking to create a pool of Unit (ie, police
officers ) using stateless beans, where the state is preserved, but
they are not attached to any session, and their behavior is
independent from the request (ie, request to generate a report). My
next question would be, is to find it it's possible to get a stateless
bean to receive JMS messages and act accordingly !
An MDB is identical to a Stateless bean in it's lifecycle. Both are
pooled and don't keep client state and each request/message that comes
in an instance is selected from the pool more or less randomly.
In terms of alternate ways to keep state, you might check out the bean
type @Singleton:
http://openejb.apache.org/singleton-ejb.html
http://openejb.apache.org/3.0/singleton-example.html
It essentially allows you to keep application scoped data without any
statics and with nice concurrency options.
Not sure if that fits with your design, but certainly could provide
options.
Feel free to keep asking questions. It's no trouble at all.
-David
On Sun, Dec 6, 2009 at 12:04 AM, Ravindranath Akila
<[email protected]> wrote:
Andy is right Mansour please do some reading on this. EJB 3.x has
Stateful
Session Beans, Stateless Session Beans and Entities (NOT Entity
Beans). The
Sun tutorial is one of the most simple tutorials you can find on
this.
Entities on the other hand, will be explained in any tutorial of
JPA. So to
find out about Entities, read a JPA tutorial. This is a very good JPA
tutorial http://schuchert.wikispaces.com/JPA+Tutorial+1+-+Getting+Started
.
Yes the same Stateful Beans cannot be retrieved across multiple "web"
requests unless you store the bean with use of a framework or HTTP
Session.
Stateful really indicates "not shared", and "not discarded as long as
referenced".
On Thu, Dec 3, 2009 at 1:44 AM, Mansour Al Akeel
<[email protected]>wrote:
I am looking to maintain an object pool, that will be available to
server a request at anytime. If I am not wrong, statfull bean will
not
work as it's ot server on request. I need to maintain the info
between
these requests. I have to use Entity bean. Is this correct ?
