Enterprise Integration Patterns
Messaging Patterns
Table of ContentsTable of ContentsMessaging Patterns

 Messaging Patterns Overview 
Table of Contents Detailed table of contents.
Solving Integration Problems using Patterns 
Integration Styles
Introduction to Integration Styles 
File TransferHow can I integrate multiple applications so that they work together and can exchange information?
Shared DatabaseHow can I integrate multiple applications so that they work together and can exchange information?
Remote Procedure InvocationHow can I integrate multiple applications so that they work together and can exchange information?
MessagingHow can I integrate multiple applications so that they work together and can exchange information?
Messaging Systems
Introduction to Messaging Systems 
Message ChannelHow does one application communicate with another using messaging?
MessageHow can two applications connected by a message channel exchange a piece of information?
Pipes and Filters How can we perform complex processing on a message while maintaining independence and flexibility?
Message RouterHow can you decouple individual processing steps so that messages can be passed to different filters depending on a set of conditions?
Message Translator How can systems using different data formats communicate with each other using messaging?
Message EndpointHow does an application connect to a messaging channel to send and receive messages?
Messaging Channels
Introduction to Messaging Channels 
Point-to-Point ChannelHow can the caller be sure that exactly one receiver will receive the document or perform the call?
Publish-Subscribe ChannelHow can the sender broadcast an event to all interested receivers?
Datatype ChannelHow can the application send a data item such that the receiver will know how to process it?
Invalid Message ChannelHow can a messaging receiver gracefully handle receiving a message that makes no sense?
Dead Letter ChannelWhat will the messaging system do with a message it cannot deliver?
Guaranteed DeliveryHow can the sender make sure that a message will be delivered, even if the messaging system fails?
Channel AdapterHow can you connect an application to the messaging system so that it can send and receive messages?
Messaging BridgeHow can multiple messaging systems be connected so that messages available on one are also available on the others?
Message Bus What is an architecture that enables separate applications to work together, but in a decoupled fashion such that applications can be easily added or removed without affecting the others?
Message Construction
Introduction to Message Construction 
Command MessageHow can messaging be used to invoke a procedure in another application?
Document MessageHow can messaging be used to transfer data between applications?
Event MessageHow can messaging be used to transmit events from one application to another?
Request-ReplyWhen an application sends a message, how can it get a response from the receiver?
Return AddressHow does a replier know where to send the reply?
Correlation IdentifierHow does a requestor that has received a reply know which request this is the reply for?
Message SequenceHow can messaging transmit an arbitrarily large amount of data?
Message ExpirationHow can a sender indicate when a message should be considered stale and thus shouldn’t be processed?
 Format IndicatorHow can a message’s data format be designed to allow for possible future changes?
Interlude: Simple Messaging
Introduction to Simple Messaging Examples 
JMS Request/Reply Example 
.NET Request/Reply Example 
JMS Publish/Subscribe Example 
Message Routing
 Introduction to Message Routing 
Content-Based Router How do we handle a situation where the implementation of a single logical function (e.g., inventory check) is spread across multiple physical systems?
Message FilterHow can a component avoid receiving uninteresting messages?
Dynamic RouterHow can you avoid the dependency of the router on all possible destinations while maintaining its efficiency?
Recipient ListHow do we route a message to a list of dynamically specified recipients?
Splitter How can we process a message if it contains multiple elements, each of which may have to be processed in a different way?
Aggregator How do we combine the results of individual, but related messages so that they can be processed as a whole?
ResequencerHow can we get a stream of related but out-of-sequence messages back into the correct order?
Composed Message Processor How can you maintain the overall message flow when processing a message consisting of multiple elements, each of which may require different processing?
Scatter-Gather How do you maintain the overall message flow when a message needs to be sent to multiple recipients, each of which may send a reply?
Routing Slip How do we route a message consecutively through a series of processing steps when the sequence of steps is not known at design-time and may vary for each message?
Process ManagerHow do we route a message through multiple processing steps when the required steps may not be known at design-time and may not be sequential?
Message BrokerHow can you decouple the destination of a message from the sender and maintain central control over the flow of messages?
Message Transformation
Introduction to Message Transformation 
Envelope Wrapper How can existing systems participate in a messaging exchange that places specific requirements on the message format, such as message header fields or encryption?
Content Enricher How do we communicate with another system if the message originator does not have all the required data items available?
Content Filter How do you simplify dealing with a large message, when you are interested only in a few data items?
Claim Check How can we reduce the data volume of message sent across the system without sacrificing information content?
NormalizerHow do you process messages that are semantically equivalent, but arrive in a different format?
 Canonical Data ModelHow can you minimize dependencies when integrating applications that use different data formats?
Interlude: Composed Messaging
Introduction to Composed Messaging Examples 
Synchronous Implementation using Web Services 
Asynchronous Implementation with MSMQ 
Asynchronous Implementation with TIBCO ActiveEnterprise 
Messaging Endpoints
Introduction to Messaging Endpoints 
Messaging GatewayHow do you encapsulate access to the messaging system from the rest of the application?
Messaging MapperHow do you move data between domain objects and the messaging infrastructure while keeping the two independent of each other?
Transactional ClientHow can a client control its transactions with the messaging system?
Polling ConsumerHow can an application consume a message when the application is ready?
Event-Driven ConsumerHow can an application automatically consume messages as they become available?
Competing ConsumersHow can a messaging client process multiple messages concurrently?
Message DispatcherHow can multiple consumers on a single channel coordinate their message processing?
Selective ConsumerHow can a message consumer select which messages it wishes to receive?
Durable SubscriberHow can a subscriber avoid missing messages while it’s not listening for them?
Idempotent ReceiverHow can a message receiver deal with duplicate messages?
Service ActivatorHow can an application design a service to be invoked both via various messaging technologies and via non-messaging techniques?
System Management
 Introduction to System Management 
Control Bus How can we effectively administer a messaging system that is distributed across multiple platforms and a wide geographic area?
DetourHow can you route a message through intermediate steps to perform validation, testing or debugging functions?
Wire TapHow do you inspect messages that travel on a point-to-point channel?
 Message History How can we effectively analyze and debug the flow of messages in a loosely coupled system?
Message Store How can we report against message information without disturbing the loosely coupled and transient nature of a messaging system?
Smart ProxyHow can you track messages on a service that publishes reply messages to the Return Address specified by the requestor?
Test Message What happens, though, if a component is actively processing messages, but garbles outgoing messages due to an internal fault?
Channel PurgerHow can you keep 'left-over' messages on a channel from disturbing tests or running systems?
Interlude: Systems Management Example
Loan Broker System Management 
Integration Patterns in Practice
 Case Study: Bond Trading System 
Concluding Remarks
 Emerging Standards and Futures in Enterprise Integration 
 Bibliography Annotated list of references and recommended reading.
 Revision History Chronological list of changes.