Event MessageMessaging Patterns » Message Construction

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Several applications would like to use event-notification to coordinate their actions, and would like to use Messaging to communicate those events.

How can messaging be used to transmit events from one application to another?

Use an Event Message for reliable, asynchronous event notification between applications.

When a subject has an event to announce, it will create an event object, wrap it in a message, and send it on a channel. The observer will receive the event message, get the event, and process it. Messaging does not change the event notification, just makes sure that the notification gets to the observer.

The difference between an Event Message and a Document Message is a matter of timing and content. An event’s contents is typically less important. Many events are empty; their mere occurrance tells the observer to react. An event’s timing is very important; the subject should issue an event as soon as a change occurs, and the observer should process it quickly while it’s still relevant. Guaranteed Delivery is usually not very helpful with events because they’re frequent and need to be delivered quickly. Message Expiration can be very helpful to make sure that an event is processed quickly or not at all.

Related patterns: Command Message, Document Message, Durable Subscriber, Remote Procedure Invocation, Guaranteed Delivery, Message, Message Expiration, Messaging, JMS Publish/Subscribe Example, Point-to-Point Channel, Publish-Subscribe Channel

Integration Pattern Language

Message Construct.

Message

Command Message

Document Message

Event Message

Request-Reply

Return Address

Correlation Identifier

Message Sequence

Message Expiration

Format Indicator

Message Routing

Pipes-and-Filters

Message Router

Content-based Router

Message Filter

Dynamic Router

Recipient List

Splitter

Aggregator

Resequencer

Composed Msg. Processor

Scatter-Gather

Routing Slip

Process Manager

Message Broker

Message
Transformation

Message Translator

Envelope Wrapper

Content Enricher

Content Filter

Claim Check

Normalizer

Canonical Data Model

Messaging Endpoints

Message Endpoint

Messaging Gateway

Messaging Mapper

Transactional Client

Polling Consumer

Event-driven Consumer

Competing Consumers

Message Dispatcher

Selective Consumer

Durable Subscriber

Idempotent Receiver

Service Activator

Messaging Channels

Message Channel

Point-to-Point Channel

Publish-Subscr. Channel

Datatype Channel

Invalid Message Channel

Dead Letter Channel

Guaranteed Delivery

Channel Adapter

Messaging Bridge

Message Bus

Systems Mgmt.

Control Bus

Detour

Wire Tap

Message History

Message Store

Smart Proxy

Test Message

Channel Purger