JMS is a very important service available to enterprise beans, so understanding its
purpose is important to this
mailing list. With the introduction of Message Driven Beans in EJB 2.0, JMS becomes
even more important to EJB.
Here is an expert from Chapter 1, of O'Reilly's JMS book, which may help you in
understanding enterprise messaging and
JMS.
O�Reilly�s JMS book, by Richard Monson-Haefel and David Chappell
http://www.amazon.com/exec/obidos/ASIN/0596000685/ref=nosim/aresoursiteforej
�Computers and people can communicate by using messaging systems to exchange messages
over electronic networks. The
most ubiquitous messaging system today is email, which facilitates communication among
people. While email is an
impor-tant human-to-human messaging system, this book is not about email. Instead,
this book is concerned with
messaging systems that allow different software applica-tions to communicate with each
other. These
application-to-application messag-ing systems, when used in business systems, are
generically referred to as
enterprise messaging systems, or Message-Oriented Middleware (MOM).
Enterprise messaging systems allow two or more applications to exchange information in
the form of messages. A
message, in this case, is a self-contained package of business data and network
routing headers. The business data
contained in a message can be anything�depending on the business scenario�and usually
contains information about some
business transaction. In enterprise messaging systems, messages inform an application
of some event or occurrence in
another system.
Messages are transmitted from one application to another on a network that uses
Message-Oriented Middleware. MOM
products ensure that messages are properly distributed among applications. In
addition, MOMs usually provide fault
tolerance, load balancing, scalability, and transactional support for enterprises that
need to reliably exchange large
quantities of messages.
MOM vendors use different message formats and network protocols for exchanging
messages, but the basic semantics are
the same. An API is used to create a mes-sage, give it a payload (application data),
assign it routing information,
and then send the message. The same API is used to receive messages produced by other
applications. �
�The Java Message Service (JMS) is a vendor-agnostic Java API that can be used with
many different MOM vendors. JMS
is very similar to JDBC in that application developers reuse the same API to access
many different systems. If a
vendor pro-vides a compliant service provider for JMS, then the JMS API can be used to
send and receive messages to
that vendor. For example, you can use the same JMS API to send messages using
Progress� SonicMQ as you do IBM�s
MQSeries. It is the purpose of this book to explain how enterprise messaging systems
work and in par-ticular how the
Java Message Service is used with these systems. This book focuses on JMS 1.0.2, the
most recent version of the
specification, which was introduced in November 1999.� ... �A key concept of
enterprise messaging is messages are
delivered asynchronously from one system to others over a network. To deliver a
message asynchronously means that the
sender is not required to wait for the message to be received or handled by the
recipient; it is free to send the
message and continue processing.�
----- end book excerpts
The chapter goes on to provide examples of real world applications that leverage
enterprise messaging systems for
things like Enterprise Application Integration (EAI), business-to-business (B2B), and
geographically dispersed
businesses.
A key reason for using JMS is that it's asynchronous. This means that business systems
can communicate even if their
is a partial failure; the system your send messages to is down. In addition JMS
supports a high quality of service
(transactions, security, durability, load-balancing, fail-over, etc.).
With JMS (or enterprise messaging in general), business systems can be added and
removed from a enterprise without
disrupting the operations of other systems. So, for example, if you wanted to
introduce a new business process, such
as auditing, into an existing system, you could do it without modifying the other
systems or taking the whole system
down. You just add the business process as a subscriber to specific types of
messages. That's a powerful concept
that is not easily be explained in an e-mail.
I suggest you read either the O�Reilly book on JMS, which I co-authored, or the WROX
book on the same subject. Once
you understand the concepts and do a couple of the tutorials you�ll understand how
powerful this technology is.
O�Reilly�s JMS book
http://www.amazon.com/exec/obidos/ASIN/0596000685/ref=nosim/aresoursiteforej
More information on JMS
http://www.jmiddleware.com/jms_main_page.html
Good luck!
Richard
--
Richard Monson-Haefel
Author of Enterprise JavaBeans, 2nd Edition (O'Reilly 2000)
Co-Author of Java Message Service (O'Reilly 2000)
http://www.jMiddleware.com
>
> > hi
> >
> > though i learn a lot of info abt Java Message Service
> > I am unable to understand the practical use of Message Broker and the type of
>applications its currently used.
> > I would like u to give me some references if possible
> >
> > _____________________________________________________
> > Chat with your friends as soon as they come online. Get Rediff Bol at
> > http://bol.rediff.com
> >
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