Java Data Objects
by Robin M. Roos

May 2003 Issue

The Java Data Objects (JDO) specification has just been finalized, and if you make frequent use of relational or object databases in your projects, you owe it to yourself to investigate this technology. JDO is intended to provide object persistence through a fairly transparent layer that doesn't force you to modify your classes. There are numerous vendors who have already released implementations that adhere to the specification, making this approach all the more useful for its standard-based focus and quickly realized availability.

Java Data Objects is divided into 13 chapters and 5 appendices, covering everything from the specification objectives to existing implementations, which included nine vendors when the book was written, with solutions ranging from JDBC abstractions to object-oriented databases. There is likely to be more vendor support by the time you read this review, given the pace at which this specification is being applied. The specification, and the book, makes clear distinctions between required and optional features, and the author does a great job of explaining each feature in well-organized detail.

The book progresses through the obvious topics, such as a chapter on understanding object persistence, followed by a few examples and an overview of the JDO architecture. After you read the first three chapters, you'll have a good sense of what JDO was meant to address. Chapter 4 looks at state transitions in the data object life cycle. Subsequent chapters take a closer look at the persistent object model, primary interfaces and classes, and transaction management. There's a full chapter dedicated to JDO Query Language and an appendix that specifies the language syntax using BNF. Other chapters cover JDO exceptions, J2EE integration, and persistence descriptors.

It's hard to fault this book for anything given its clarity of purpose and execution. The only thing that stumped me periodically was a pattern of launching into detailed explanations without a clear preamble. This caveat is pretty minor, though, because the context makes things clear within a few paragraphs. Overall, I enjoyed reading this book, both because the topics were interesting and because the author presents the information in a clear, easy-to-read style that provides the reader effortless understanding. JDO may well be a key Java technology, certainly one worth investigating at this stage. This book makes it easy to stay on top of the JDO specification.

—Claude Duguay