Foreword by Martin Fowler

ThoughtWorks started to work with J2EE in late 1998. At that time we found a lot of cool (if somewhat immature) technology, but with little guidance on how to use it well. We coped, partly because we had a lot of experience in other OO server environments. But we've seen many clients who've struggled, not because of problems in the technology - but due to not knowing how to use it well.

For many years I've been a big fan of patterns as a way to capture design expertise - to catalog practical solutions to recurring problems. Over the last couple of years various pioneers have been working with J2EE and uncovering the patterns that make for an effective J2EE solution. This book is an excellent collection of those patterns, capturing many of the techniques that we had to discover by trial and error.

That's why this book is important. Knowing the APIs backwards is one thing; knowing how to design good software is something else. This book is the first book I've seen that's really concentrated on capturing this design knowledge, and I'm relieved to see they've done a damned fine job of doing it. If you're working with J2EE you need to be aware of these patterns.

Furthermore, this book recognizes that design doesn't end when you start writing code. People make decisions that don't turn out that way. In this situation you need to fix your design and you need to fix it in a disciplined way. Refactoring is increasingly the approach of choice for making changes to an existing system. The authors are the first group to extend my work on refactoring into a new direction-into the world of J2EE design. Not just am I grateful that someone has built on my earlier work, I'm glad they've used their experience to outline how to do these transformations.

In the end, it's that experience that counts. Capturing design experience in books is one of the hardest things to do, yet is so necessary for our profession to grow. This book captures vital experience for J2EE development. Don't build an enterprise bean without it.

Martin Fowler
Chief Scientist
ThoughtWorks, Inc.