List of Patterns Aggregator (268) How do we combine the Document Message (147) How can messaging results of individual but related messages so D be used to transfer data between applications? that they can be processed as a whole? Durable Subscriber (522) How can a subscriber Canonical Data Model (355) How can you avoid missing messages while it’s not listening for minimize dependencies when integrating them? applications that use different data formats? Dynamic Router (243) How can you avoid the Channel Adapter (127) How can you connect dependency of the router on all possible destina- an application to the messaging system so that tions while maintaining its efficiency? it can send and receive messages? Envelope Wrapper (330) How can existing sys- Channel Purger (572) How can you keep left- tems participate in a messaging exchange that plac- over messages on a channel from disturbing es specific requirements, such as message header tests or running systems? fields or encryption, on the message format? Claim Check (346) How can we reduce the Event Message (151) How can messaging be data volume of message sent across the system E used to transmit events from one application to without sacrificing information content? another? Command Message (145) How can messaging Event-Driven Consumer (498) How can an C be used to invoke a procedure in another application automatically consume messages application? as they become available? Competing Consumers (502) How can a File Transfer (43) How can I integrate multiple messaging client process multiple messages applications so that they work together and can concurrently? exchange information? Composed Message Processor (294) How can Format Indicator (180) How can a message’s you maintain the overall message flow when pro- data format be designed to allow for possible cessing a message consisting of multiple elements, future changes? each of which may require different processing? Guaranteed Delivery (122) How can the sender Content Enricher (336) How do we communi- make sure that a message will be delivered even cate with another system if the message origina- if the messaging system fails? tor does not have all the required data items Idempotent Receiver (528) How can a message available? receiver deal with duplicate messages? Content Filter (342) How do you simplify Invalid Message Channel (115) How can a mes- dealing with a large message when you are saging receiver gracefully handle receiving a mes- interested only in a few data items? sage that makes no sense? Content-Based Router (230) How do we han- Message Broker (322) How can you decouple dle a situation in which the implementation the destination of a message from the sender of a single logical function is spread across and maintain central control over the flow of multiple physical systems? messages? Control Bus (540) How can we effectively Message Bus (137) What architecture enables administer a messaging system that is distri- separate applications to work together but in a de- buted across multiple platforms and a wide coupled fashion such that applications can be eas- geographic area? ily added or removed without affecting the others? Correlation Identifier (163) How does a re- Message Channel (60) How does one applica- A B questor that has received a reply know which tion communicate with another using messaging? request this is the reply for? Message Dispatcher (508) How can multiple Datatype Channel (111) How can the applica- consumers on a single channel coordinate their tion send a data item such that the receiver message processing? will know how to process it? Message Endpoint (95) How does an applica- Dead Letter Channel (119) What will the mes- tion connect to a messaging channel to send and saging system do with a message it cannot deliver? receive Messages? Detour (545) How can you route a message Message Expiration (176) How can a sender through intermediate steps to perform valida- indicate when a message should be considered tion, testing, or debugging functions? stale and thus shouldn’t be processed? Message Filter (237) How can a component Publish-Subscribe Channel (106) How can the avoid receiving uninteresting messages? sender broadcast an event to all interested Message History (551) How can we effectively receivers? analyze and debug the flow of messages in a Recipient List (249) How do we route a mes- loosely coupled system? sage to a dynamic list of recipients? Message Router (78) How can you decouple Remote Procedure Invocation (50) How can I individual processing steps so that messages integrate multiple applications so that they work can be passed to different filters depending on together and can exchange information? a set of conditions? Request-Reply (154) When an application sends 1 2 3 Message Sequence (170) How can messaging a message, how can it get a response from the transmit an arbitrarily large amount of data? receiver? Message Store (555) How can we report against Resequencer (283) How can we get a stream of message information without disturbing the related but out-of-sequence messages back into loosely coupled and transient nature of a the correct order? messaging system? Return Address (159) How does a replier know Message Translator (85) How can systems where to send the reply? using different data formats communicate with Routing Slip (301) How do we route a message each other using messaging? consecutively through a series of processing Message (66) How can two applications con- steps when the sequence of steps is not known nected by a message channel exchange a piece at design time and may vary for each of information? message? Messaging Bridge (133) How can multiple mes- Scatter-Gather (297) How do you maintain the saging systems be connected so that messages overall message flow when a message must be available on one are also available on the others? sent to multiple recipients, each of which may Messaging Gateway (468) How do you encap- send a reply? sulate access to the messaging system from the Selective Consumer (515) How can a message ? rest of the application? consumer select which messages it wishes to Messaging Mapper (477) How do you move receive? data between domain objects and the messaging Service Activator (532) How can an application infrastructure while keeping the two indepen- design a service to be invoked both via various dent of each other? messaging technologies and via non-messaging Messaging (53) How can I integrate multiple techniques? applications so that they work together and Shared Database (47) How can I integrate mul- can exchange information? tiple applications so that they work together and Normalizer (352) How do you process messag- can exchange information? es that are semantically equivalent but arrive in a Smart Proxy (558) How can you track messages different format? on a service that publishes reply messages to the Pipes and Filters (70) How can we perform Return Address specified by the requestor? complex processing on a message while main- Splitter (259) How can we process a message if taining independence and flexibility? it contains multiple elements, each of which may Point-to-Point Channel (103) How can the have to be processed in a different way? caller be sure that exactly one receiver will Test Message (569) What happens if a compo- receive the document or perform the call? nent is actively processing messages but garbles Polling Consumer (494) How can an applica- outgoing messages due to an internal fault? tion consume a message when the application Transactional Client (484) How can a client is ready? control its transactions with the messaging Process Manager (312) How do we route a mes- system? sage through multiple processing steps when the Wire Tap (547) How do you inspect messages required steps may not be known at design time that travel on a Point-to-Point Channel? and may not be sequential? Enterprise Integration Patterns The Addison-Wesley Signature Series Kent Beck, Mike Cohn, and Martin Fowler, Consulting Editors Visit informit.com/awss for a complete list of available products. he Addison-Wesley Signature Series provides readers with Tpractical and authoritative information on the latest trends in modern technology for computer professionals. The series is based on one simple premise: Great books come from great authors. Books in the series are personally chosen by expert advisors, world-class authors in their own right. These experts are proud to put their signatures on the covers, and their signatures ensure that these thought leaders have worked closely with authors to define topic coverage, book scope, critical content, and overall uniqueness. The expert signatures also symbolize a promise to our readers: You are reading a future classic. Enterprise Integration Patterns Designing, Building, and Deploying Messaging Solutions Gregor Hohpe Bobby Woolf With Contributions by Kyle Brown Conrad F. D’Cruz Martin Fowler Sean Neville Michael J. Rettig Jonathan Simon Boston • San Francisco • New York • Toronto • Montreal London • Munich • Paris • Madrid Capetown • Sydney • Tokyo • Singapore • Mexico City Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and Addison- Wesley was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals. The authors and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein. The publisher offers discounts on this book when ordered in quantity for bulk purchases and special sales. For more information, please contact: U.S. Corporate and Government Sales (800) 382-3419 [email protected] For sales outside of the U.S., please contact: International Sales (317) 581-3793 [email protected] Visit Addison-Wesley on the Web: www.awprofessional.com Library of Congress Cataloging-in-Publication Data Hohpe, Gregor.