Thank you Per!!
The origin of this confusion is a sample in JBoss Documentation,
making more specific: example called "MDB as a Listener".
How many "subscribers" appear in this example?
I think a subscriber is 'Worker Bean', isn't it?
Then, to have more than one subscriber i've to create other Beans
similar (or not) to Worker Bean, haven't i?
So, if i create new beans i have to modify my Listener to be able to
comunicate with the new subscriber...
Please, am i in the correct way?
Thank you again!
__________________________________________
Jaume Soriano Sivera <[EMAIL PROTECTED]>
Tel: 965040000 -ext. 44744 Fax: 965040047
Portal y servicios multimedia - Nuevas tecnologias
W a n a d o o E s p a n a - http://www.wanadoo.es
__________________________________________
Per Lewau <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
14/05/2001 13:08
Please respond to jboss-user
To: [EMAIL PROTECTED]
cc:
Subject: Re: [JBoss-user] MDB...why?
On Mon, 14 May 2001 [EMAIL PROTECTED] wrote:
> Hi:
> I'm testing JBoss with MDB but i'm still lost about its
> utility...
> I'd like to write an application to manage a little
> "web-shop" using EJBs and MDBs as follows:
>
> * A java servlet who takes data from web application, i.e.
> the identifier of a client who wants to buy a book.
>
> * Before allowing this purchase i want to check if this client
> is not in my 'defaulter list'.
>
> * After this i'll be able to avoid/allow the purchase.
>
> Well, i though to do this:
>
> "The servlet takes data from web client and sends it to a Topic,
> then Topic sends data to a Checker Bean that runs a method
> called 'checkClient' wich look for this client in a 'defaulter'
database.
> If everything is ok, a 'true' value is returned to servlet"
Sounds more like a Queue than a Topic to me. Queues are for point-to-point
messages and Topics are for Publisher/Subscriber (many receivers).
> Is this a good way to pose my problem?
> I know its possible to develope *the same* without MDBs, but,
> is there any advantage on using MDBs?
> in other words, how can i take advantage of MDBs?
I'm not sure what you are trying to do, but this is my take on what you
want.
0. MDB listens for messages on in queue
1. serlvet sends message to in queue with whatever should be checked
2. servlet waits for message on out queue
3. MDB.onMessage() called
4. MDB checks whatever
5. MDB sends message (true or false) to out queue
6. servlet receives message and proceeds
I'd say that the advantage of MDBs is that they can be called
asynchronously. What you want to do sound synchronous and while possible
to do it just adds a lot of overhead. A session bean is easier and faster.
To me it seems as though MDBs are useful for triggering some action that
you don't want to hang around waiting for. For instance, you might want to
send an email with an order confirmation and personally I wouldn't want to
hang around in my "process order" session bean waiting for JavaMail to
finish (after all it is talking SMTP to a mail server somewhere) so I
would simple put a message in a queue and let an MDB deal with the sending
of emails.
Regards, Per
-----------------------------------------------------------------------
Per Lewau ([EMAIL PROTECTED])
"Why waste time learning, when ignorance is instantaneous?"
- Hobbes
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