Enterprise Integration PatternsMessaging Patterns
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Pipes and FiltersPipes and Filters

Messaging Patterns

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In many enterprise integration scenarios, a single event triggers a sequence of processing steps, each performing a specific function. For example, let's assume a new order arrives in our enterprise in the form of a message. One requirement may be that the message is encrypted to prevent eavesdroppers from spying on a customer's order. A second requirement is that the messages contain authentication information in the form of a digital certificate to ensure that orders are placed only by trusted customers. In addition, duplicate messages could be sent from external parties (remember all the warnings on the popular shopping sites to click the 'Order Now' button only once?). To avoid duplicate shipments and unhappy customers, we need to eliminate duplicate messages before subsequent order processing steps are initiated. To meet these requirements, we need to transform a stream of possibly duplicated, encrypted messages containing extra authentication data into a stream of unique, simple plain-text order messages without the extraneous data fields.

How can we perform complex processing on a message while maintaining independence and flexibility?

Use the Pipes and Filters architectural style to divide a larger processing task into a sequence of smaller, independent processing steps (Filters) that are connected by channels (Pipes).

Each filter exposes a very simple interface: it receives messages on the inbound pipe, processes the message, and publishes the results to the outbound pipe. The pipe connects one filter to the next, sending output messages from one filter to the next. Because all component use the same external interface they can be composed into different solutions by connecting the components to different pipes. We can add new filters, omit existing ones or rearrange them into a new sequence -- all without having to change the filters themselves. The connection between filter and pipe is sometimes called port. In the basic form, each filter component has one input port and one output port.

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Related patterns: Competing Consumers, Content Filter, Event-Driven Consumer, Message Filter, Message Channel, Message Router, Messaging, Messaging Gateway, Point-to-Point Channel, Resequencer, Test Message, Transactional Client


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Enterprise Integration Patterns Find the full description of this pattern in:
Enterprise Integration Patterns
Gregor Hohpe and Bobby Woolf
ISBN 0321200683
650 pages
Addison-Wesley
Creative Commons Attribution License Parts of this page are made available under the Creative Commons Attribution license. You can reuse the pattern icon, the pattern name, the problem and solution statements (in bold), and the sketch under this license. Other portions of the text, such as text chapters or the full pattern text, are protected by copyright.


Table of Contents
Preface
Introduction
Solving Integration Problems using Patterns
Integration Styles
File Transfer
Shared Database
Remote Procedure Invocation
Messaging
Messaging Systems
Message Channel
Message
Pipes and Filters
Message Router
Message Translator
Message Endpoint
Messaging Channels
Point-to-Point Channel
Publish-Subscribe Channel
Datatype Channel
Invalid Message Channel
Dead Letter Channel
Guaranteed Delivery
Channel Adapter
Messaging Bridge
Message Bus
Message Construction
Command Message
Document Message
Event Message
Request-Reply
Return Address
Correlation Identifier
Message Sequence
Message Expiration
Format Indicator
Interlude: Simple Messaging
JMS Request/Reply Example
.NET Request/Reply Example
JMS Publish/Subscribe Example
Message Routing
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
Envelope Wrapper
Content Enricher
Content Filter
Claim Check
Normalizer
Canonical Data Model
Interlude: Composed Messaging
Synchronous (Web Services)
Asynchronous (MSMQ)
Asynchronous (TIBCO)
Messaging Endpoints
Messaging Gateway
Messaging Mapper
Transactional Client
Polling Consumer
Event-Driven Consumer
Competing Consumers
Message Dispatcher
Selective Consumer
Durable Subscriber
Idempotent Receiver
Service Activator
System Management
Control Bus
Detour
Wire Tap
Message History
Message Store
Smart Proxy
Test Message
Channel Purger
Interlude: Systems Management Example
Instrumenting Loan Broker
Integration Patterns in Practice
Case Study: Bond Trading System
Concluding Remarks
Emerging Standards
Appendices
Bibliography
Revision History