This book does not provide any defined solutions or silver bullets. Integrating J2EE Platform applications with legacy systems is a difficult task that requires a thorough understanding of both legacy system applications and object-oriented design. We have tried to find a practical approach to applying the J2EE integration tier patterns in real-world situations, the main design principle being that of separation of concerns. Some of the designs described in this book are currently running in production, while others represent theoretical work that has not yet been tested in a full-scale production environment. We hope, however, that in reading this book you will gain valuable tools with which to start the long journey toward application integration.