Message RouterMessaging Patterns » Messaging Systems

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Multiple processing steps in a Pipes and Filters chain are connected by Message Channels.

How can you decouple individual processing steps so that messages can be passed to different filters depending on a set of conditions?

Insert a special filter, a Message Router, which consumes a Message from one Message Channel and republishes it to a different Message Channel channel depending on a set of conditions.

The Message Router differs from the most basic notion of Pipes and Filters in that it connects to multiple output channels. Thanks to the Pipes and Filters architecture the components surrounding the Message Router are completely unaware of the existence of a Message Router. A key property of the Message Router is that it does not modify the message contents. It only concerns itself with the destination of the message.

The key benefit of using a Message Router is that the decision criteria for the destination of a message are maintained in a single location. If new message types are defined, new processing components are added, or the routing rules change, we need to change only the Message Router logic and all other components remain unaffected. Also, since all messages pass through a single Message Router, incoming messages are guaranteed to be processed one-by-one in the correct order.

Related patterns: Channel Adapter, Content-Based Router, Control Bus, Datatype Channel, Dynamic Router, Message Filter, Message, Message Channel, Message History, Introduction to Message Routing, Message Translator, Pipes and Filters, Publish-Subscribe Channel, Transactional Client

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