What Are Patterns?

Strategies for Enterprise JavaBeans

The history of software development is quite short when compared to other engineering disciplines. This is why software is often seen as an immature profession relative to other technical fields. Accumulating proven patterns that are shared by the developer community is a way to further its progress toward maturity. Some results of this progress are seen each time the bar is raised on what parts of a program an application developer is responsible for designing and coding. Just as standard communications functionality built on top of TCP/IP freed developers from networking details, EJB uses many proven ideas for transactional processing and distributed application development to move developers to an even higher level.

When you build an EJB application, you are taking advantage of the past experience of EJB's designers without having to readdress problems that have been handled for you. Everything that happens under the hood uses tested solutions so that you don't have to reinvent the wheel each time you build an application.

Just as software is a young discipline compared to many others, EJB is young compared to other software approaches. It's of course an evolution of what's been done already with transactional and distributed systems, but there's still knowledge to be gained about how to best build applications on top of EJB. The goal of this chapter is to introduce you to some of the knowledge that's been accumulated so far by the EJB development community. Some of the ideas presented here can be described as patterns, and some others are more like strategies to consider when designing part of an EJB application. This isn't a patterns book, so a formal approach for presenting this material is avoided here. The intent is more to convey the importance of understanding design patterns and these proposed strategies for building EJB applications. Both are very important in building resilient software systems.

Before getting to the details, we want to make it clear that we're not the first to understand the importance of these strategies. We are merely documenting approaches that are taking shape within EJB development that we have found to be useful while building our own EJB applications. The ideas presented in this chapter come from such sources as Web sites, mailing lists, newsgroups, articles, other books, and of course, our own experiences. Just as many of the GoF patterns have become ingrained in the software development industry, several of the concepts summarized here are approaching similar status among EJB developers. Many of the design approaches presented here have evolved from the work of several sources, so it's difficult to give credit to individuals for these ideas just as it's difficult to credit sources for the ideas that went into the EJB specification. Our goal is to assist in promoting these approaches and sharing them with as many designers and developers as possible to help raise the bar of our craft once again.