Read an Excerpt
This is a book about enterprise integration using messaging. It does not document any particular technology or product. Rather, it is designed for developers and integrators using a variety of messaging products and technologies, such as
Enterprise integration goes beyond creating a single application with a distributed n-tier architecture, which enables a single application to be distributed across several computers. Whereas one tier in a distributed application cannot run by itself, integrated applications are independent programs that can each run by themselves, yet that function by coordinating with each other in a loosely coupled way. Messaging enables multiple applications to exchange data or commands across the network using a "send and forget" approach. This allows the caller to send the information and immediately go on to other work while the information is transmitted by the messaging system. Optionally, the caller can later be notified of the result through a callback. Asynchronous calls and callbacks can make a design more complexthan a synchronous approach, but an asynchronous call can be retried until it succeeds, which makes the communication much more reliable. Asynchronous messaging also enables several other advantages, such as throttling of requests and load balancing.Who Should Read This Book
This book is designed to help application developers and system integrators connect applications using message-oriented integration tools:
This book does not attempt to make a business case for enterprise application integration; the focus is on how to make it work. You will learn how to integrate enterprise applications by understanding the following:
We believe that any book sporting the word "enterprise" in the title is likely to fall into one of three categories. First, the book might attempt to cover the whole breadth of the subject matter but is forced to stop short of detailed guidance on how to implement actual solutions. Second, the book might provide specific hands-on guidance on the development of actual solutions but is forced to constrain the scope of the subject area it addresses. Third, the book might attempt to do both but is likely never to be finished or else to be published so late as to be irrelevant. We opted for the second choice and hopefully created a book that helps people create better integration solutions even though we had to limit the scope of the book. Topics that we would have loved to discuss but had to exclude in order not to fall into the category-three trap include security, complex data mapping, workflow, rule engines, scalability and robustness, and distributed transaction processing (XA, Tuxedo, and the like). We chose asynchronous messaging as the emphasis for this book because it is full of interesting design issues and trade-offs, and provides a clean abstraction from the many implementations provided by various integration vendors.
This book is also not a tutorial on a specific messaging or middleware technology. To highlight the wide applicability of the concepts presented in this book, we included examples based on a number of different technologies, such as JMS, MSMQ, TIBCO, BizTalk, and XSL. However, we focus on the design decisions and trade-offs as opposed to the specifics of the tool. If you are interested in learning more about any of these specific technologies, please refer to one of the books referenced in the bibliography or to one of the many online resources.How This Book Is Organized
As the title suggests, the majority of this book consists of a collection of patterns. Patterns are a proven way to capture experts' knowledge in fields where there are no simple "one size fits all" answers, such as application architecture, object-oriented design, or integration solutions based on asynchronous messaging architectures.
Each pattern poses a specific design problem, discusses the considerations surrounding the problem, and presents an elegant solution that balances the various forces or drivers. In most cases, the solution is not the first approach that comes to mind, but one that has evolved through actual use over time. As a result, each pattern incorporates the experience base that senior integration developers and architects have gained by repeatedly building solutions and learning from their mistakes. This implies that we did not "invent" the patterns in this book; patterns are not invented, but rather discovered and observed from actual practice in the field.
Because patterns are harvested from practitioners' actual use, chances are that if you have been working with enterprise integration tools and asynchronous messaging architectures for some time, many of the patterns in this book will seem familiar to you. Yet, even if you already recognize most of these patterns, there is still value in reviewing this book. This book should validate your hard-earned understanding of how to use messaging while documenting details of the solutions and relationships between them of which you might not have been aware. It also gives you a consolidated reference to help you pass your knowledge effectively to less-experienced colleagues. Finally, the pattern names give you a common vocabulary to efficiently discuss integration design alternatives with your peers.
The patterns in this book apply to a variety of programming languages and platforms. This means that a pattern is not a cut-and-paste snippet of code, but you have to realize a pattern to your specific environment. To make this translation easier, we added a variety of examples that show different ways of implementing patterns using popular technologies such as JMS, MSMQ, TIBCO, BizTalk, XSL, and others. We also included a few larger examples to demonstrate how multiple patterns play together to form a cohesive solution.
Integrating multiple applications using an asynchronous messaging architecture is a challenging and interesting field. We hope you enjoy reading this book as much as we did writing it.About the Cover Picture
The common theme for books in the Martin Fowler Signature Series is a picture of a bridge. In some sense we lucked out, because what theme would make a better match for a book on integration? For thousands of years, bridges have helped connect people from different shores, mountains, and sides of the road.
We selected a picture of the Taiko-bashi Bridge at the Sumiyoshi-taisha Shrine in Osaka, Japan, for its simple elegance and beauty. As a Shinto shrine dedicated to the guardian deity for sailors, it was originally erected next to the water. Interestingly, land reclamation has pushed the water away so that the shrine today stands almost three miles inland. Some three million people visit this shrine at the beginning of a new year.
San Francisco, California
Raleigh, North Carolina