J2EE Design Patterns

Message Distribution Patterns

Message distribution is built around the concept of a message channel , which happens to be the fundamental idiom behind the JMS API. A message channel provides a named destination for messages. Senders can access the channel to send messages, and receivers can read messages off the channel. It’s that simple. In the email world, a message channel consists of the combination of SMTP (for sending and transport) and a mailbox (for receipt). In JMS, a channel is represented as either a Queue or a Topic object, for point-to-point or publish-subscribe messaging, respectively. In a MOM environment, channels can be created and destroyed on the fly, or you can preconfigure them within the MOM system.

Point-to-Point Distribution Pattern

The simplest form of messaging is from one actor to one other actor. This situation applies when using messaging to perform remote procedure calls or to deliver document messages for processing by a particular server. In these cases, it is important that a request be sent once and only once, and that the message be received and processed once and only once. The Point-to-Point Distribution pattern defines this behavior for our applications.

In the ubiquitous purchasing system example, a purchase order should only be sent once, and should only be fulfilled once. This requirement is particularly important when messaging is used to tie together parts of a process: a message sent by an order handler requesting credit card processing ...