Hello Richard,
On this particular topic and following a previous thread, I felt a bit alone
... so I appreciate we speak again about MDBs ;)
While it is true that the JMS spec cannot guarantee to conserve the original
message sequence, it is also true that if using some specific policy for a
project (for example: all message are persisted, they all have the same
priority, etc.) we can preserve the messages sequence between a source and a
destination (in short).
The problem then with MDB is that as multiple MDB may be activated to read
the messages from the same queue, we loose the just guaranteed sequence (and
it is not possible to tell the EJB server to serialize the calls for a
particular queue (not in a standard way I mean) in order to conserve our
sequence ordering.)
As you seem quite well informed on the JMS/MDB topic, could you please
comment on this? Any hint?
Thank you. Cheers,
Sacha
> -----Message d'origine-----
> De : A mailing list for Enterprise JavaBeans development
> [mailto:[EMAIL PROTECTED]]De la part de Richard Monson-Haefel
> Envoye : vendredi, 19 janvier 2001 17:05
> A : [EMAIL PROTECTED]
> Objet : Re: what is the use of MDB?
>
>
> Message-driven beans are stateless, server-side components that
> are used to
> receive and process messages that Java clients send to them via
> JMS. They are
> used to model processes and routers that operate on inbound enterprise
> messages. Developers might use message-driven beans to integrate
> an EJB system
> with a legacy system, or to enable business-to-business
> interactions. While a
> message-driven bean consists of a bean class and an XML
> deployment descriptor,
> it does not have a remote or home interface. Message-driven beans are not
> distributed components, and do not have EJBObject and EJBHome
> references; they
> respond only to asynchronous messages delivered from JMS.
>
> In the future message-driven beans may be specified for other
> message systems
> such as SMTP, but EJB 2.0 only supports JMS based message-driven beans.
> Contrary to other comments on this list, MDB can receive also
> send JMS messages
> using the JMS API, just like any other enterprise bean can send a JMS
> messages. But they are driven, hence the name, by incoming JMS messages.
>
> --
> Richard Monson-Haefel
> Author of Enterprise JavaBeans, 2nd Edition (O'Reilly 2000)
> Co-Author of Java Message Service (O'Reilly 2000)
> http://www.EjbNow.com
>
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