Introduction

Java data objects (JDO) specifies a transparent persistence service for Java objects. The specification describes a general framework for storing and retrieving the persistent state of Java objects. The JSR-12 expert group defined JDO using the Java Community Process. JDO includes a specification, a reference implementation, and a technology compatibility kit (TCK). All three can be downloaded from the Java Community Process Web site (http://www.jcp.org/jsr/detail/12.jsp). A number of vendors have created implementations of JDO and provide versions of their products that you can download from the Web. URLs to some of these vendors are found near the end of this introduction.

Java programmers use tools to make their projects successful. Most applications and server-side components involve moving data between objects in memory and persistent storage. JDO promises to change the way that Java programmers store and retrieve object state. JDO simplifies the application's code, increases the application's portability, and helps to separate concerns in the application's design. Compared to existing alternatives, JDO makes persistence easier to understand, easier to model, and easier to code.

Who Should Read This Book

This book is intended for Java programmers and application architects. It assumes that you know how to program in Java, and it assumes that you want to use JDO and understand how it works. This book emphasizes what you need to know to use JDO effectively.

By no means do you need to understand everything in this book to use JDO effectively. JDO encapsulates many of the details of data storage, and for that reason, it is easy to use. Paradoxically, because much of what is familiar about storing and fetching data is hidden from view, JDO can be confusing. This book attempts to give you more than enough information to understand the details of JDO and its behavior. Depending on your background, temperament, and current needs, you may find there are parts of this book that you can skim or skip.

JDO has the simplicity of a violin. It is easy to pick up, and it almost instantly produces sounds. But if your purpose is to produce music, knowledge and skill are required. The purpose of this book is to help you acquire the knowledge and skill needed to use JDO successfully.