Preface

So, you want to build enterprise applications?

Back in 1996, we were working on a web-based clinical data management system for a major Boston hospital. Java 1.0.2 had recently been released, and development tools were beginning to trickle onto the market. The Write Once, Run Anywhere promise of Java was beguiling, not in the least because we didn't have development environments that mirrored the deployment environments. And here was this object-oriented, strongly typed language with—even then—an excellent standard class library. It seemed like a perfect fit, at least in theory. In the end, the application sprouted several Java applets and an early, crude database-backed web site. Replacing Perl scripts with Java code required some fancy footwork, since none of the available web servers had any native Java integration. Performance was questionable, maintenance was iffy, and at a few points we found ourselves backtracking to Perl and C++. The application itself turned into a strange amalgamation of Perl CGI scripts, server-side Java applications (including part of a custom-built web server), HTML, and C++ CGI programs.

Our primary problem was that the necessary infrastructure for both developing and deploying the application just wasn't in place. Java's support for relational databases was primitive, and while the language has always supported certain operations as a web client, it wasn't until the Java Servlet API was introduced the following year that Java gained a standard, high performance mechanism for integrating into a web server. These limitations meant that while we could use Java for some of our development activities, those activities were sharply bounded. It also meant that we couldn't take much with us as we moved on to future projects with different environments and tool sets, all of which behaved more or less differently.

Now, Java has found its place in the enterprise world. Performance is competitive with any approach you care to name. The APIs that have been added during the subsequent four iterations of the language give Java broader native support for enterprise activities than any other language available. From a standing start when we first tried it in 1996, Java has become the lingua franca for server-side business programming. The cross-platform graphical user interface, which seemed to be the most promising aspect of Java, is only now beginning to take off in a real way, mostly in products focused on developers and system administrators. But Java has taken off behind the scenes for building e-commerce web sites, intranet business applications, and mission-critical distributed computing systems. Millions of people interact with enterprise Java every day, often without realizing it.

Even if we'd had the full resources of the modern Java environment available to us, success wouldn't be guaranteed. (Actually, the application in question worked out pretty well overall, but it's not an experience that we'd like to repeat.) Tools can be used poorly or inefficiently, and the sheer scope of the J2EE environment—which now includes thousands of classes—means that very few individual developers have built up a reservoir of experience in every area. J2EE has created standards and made implementation easier, but the fundamental design issues are still as relevant as ever. We just have more ways to tackle them and more tools to eliminate the grunt work. And, of course, a standard, consistent, widely deployed platform to build those solutions on.

This is a book about building effective applications for enterprise environments, using Java 2, Enterprise Edition ( J2EE). This book is not about how to use the individual components of the J2EE specification, although we touch upon aspects of most of the components; a brief overview is provided below. Rather, this book is about the patterns that underlie effective software designs.

In addition to 12 combined years of experience building Enterprise Java systems, the authors, like the development community at large, have been the beneficiaries of over a decade of research and writing on object-oriented modeling, software design methodologies, and enterprise architecture. One of the most important ideas to gain prominence during this time is the software design pattern: a way of describing recurring solutions to common problems. This book is about the fusion of design patterns and enterprise design.