Java Message Service (JMS) for J2EE
From Publisher:
The authoritative guide to JMS for enterprise developers. JMS API is gaining important popularity for Enterprise applications and there is no adequate documentation for JMS for the J2EE platform. This book covers not only the concepts, but also present simple examples to explain the concepts and real sample applications to show how to use those concepts and techniques.
J2EE is commonly used for enterprise applications. The Java(tm) Message Service (JMS) API has been developed by Sun working in close cooperation with the leading enterprise messaging vendors. Enterprise messaging is now recognized as an essential tool for building enterprise applications. By combining Java technology with enterprise messaging, the JMS API provides a new, powerful tool for solving enterprise computing problems. Enterprise messaging provides a reliable, flexible service for the asynchronous exchange of critical business data and events throughout an enterprise. The JMS API adds to this a common API and provider framework that enables the development of portable, message based applications in the Java programming language.
Chapter 5: Concepts and Fundamentals of JMS Programming
In this chapter, you will learn the fundamentals and basic
elements of Java Message Service (JMS) programming. In the next
chapter, you will write three simple programs to help you
understand how to develop a JMS application.
What Is a Messaging System or Service?
Messaging is a way or a mechanism that provides communication
between software applications, programs, or objects on a
distributed system. Remote Method Invocation (RMI) and socket
programming are also types of messaging according to this
definition. But, the focus of this book is on a message-based
messaging system. As a simple definition, a message identifies
the content transmitted between two or more applications or
programs. One or more programs send a message, and the other one
or more programs receive the message. You might think that a
query from a SQL-based database using a graphical user interface
(GUI) is a message. It is direct, one-to-one messaging, but a
messaging system is more sophisticated than this simple example.
It is more like using TCP/IP packets on a computer network. In a
messaging system, there are clients that can send and receive
messages. Each client connects to the messaging system, which
provides a platform to create, send, and receive messages. A
messaging system has three major features:
-
A messaging system is loosely coupled. This is the most
important feature of a messaging system and might be an
advantage compared to other systems such as RMI. An application
or program, called a sender or publisher, sends a
message to a destination, not directly to another client.
Another application or program, called a receiver or
subscriber, receives the message from a destination. Senders
and receivers do not have to be aware of each other.
-
A messaging system isolates clients from each other. Neither
sender nor receiver needs to know about each other. They only
need to know the message format and destination.
-
A messaging system allows decoupling. A sender and receiver
use the system at different times. They do not have to be up and
running at the same time. A sender sends the message to a
destination, and the receiver takes the messages whenever it is
ready. A sender does not need to wait for a response. It can
process another task without being blocked. I refer to this
feature as asynchronous messaging in the remainder of the
book, which generally means that clients are able to use the
system at different times, and they do not have to know whether
other clients in the system are up and running.
Some developers consider email a part of a messaging system.
Although email is a way of communication between people, and
sometimes between people and software applications, a messaging
system is different. It is used for communication between
software applications or objects.
A messaging system is based on message-oriented middleware
(MOM), which was explained in the previous chapter. MOM defines
the rule of messaging as:
-
How the message looks
-
How a sender application sends the message
-
How a receiver application receives the message
-
How a receiver application reads the message
Advantages and Disadvantages of a Messaging System
In the messaging service (or system), there is a server, and
clients connect to this server to communicate with each other
(see Figure
5.1).
Figure 5.1
The messaging service architecture.
The server provides some essential services such as message
persistence, load balancing, and security. The server provides
asynchronous communication and guaranteed delivery from senders
to receivers.
A messaging service is a great way for applications to
communicate with each other, but it has some disadvantages:
-
You have to send header and other information with the
message content. Therefore, the total amount of information is
larger than the message content itself, which might increase
network traffic.
-
Every message goes to the receivers through a server, which
makes communication slower than a direct connection.
-
Your messaging service provider (vendor) might not support
all the JMS specifications defined by Sun Microsystems.
Before designing your JMS projects, you should compare the
disadvantages such as network traffic, slower communication, and
vendor-specific issues with the advantages such as loosely
coupled or decoupled systems, portability, persistent messaging,
and guaranteed delivery.
Briefly, if you only need to insert some new records into a
local database and you have a very reliable network, you might
not need to use a messaging system. Keep in mind that a
messaging-based application consumes additional resources.
However, if you want to isolate networking problems in your
client source code or if the database you want to access is in a
different location, you might need to use a messaging service. A
messaging service can ensure completion of transactions of an
application properly such as manipulating data in a table of the
database (for example, Insert, Delete, and Update statements),
particularly if the database is unavailable (such as when using
a laptop that is disconnected from the network). It will process
the command (the message content) at a later time. Decoupling or
loosely coupling is the best feature of a messaging service.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
| 
