Hibernate: A Developer's Notebook

Preface

Hibernate is a lightweight object/relational mapping service for Java. What does that mean? It's a way to easily and efficiently work with information from a relational database in the form of natural Java objects. But that description doesn't come close to conveying how useful and exciting the technology is. I'm not the only person who thinks so: Hibernate 2.1 just won Software Development magazine's 14th annual Jolt Award in the "Libraries, Frameworks, and Components" category.

So, what's great about Hibernate? Every nontrivial application (and even many trivial ones) needs to store and use information, and these days this usually involves a relational database. Databases are a very different world than Java objects, and they often involve people with different skills and specializations. Bridging between the two worlds has been important for a while, but it used to be quite complex and tedious.

Most people start out struggling to write a few SQL queries, embedding these awkwardly as strings within Java code, and working with JDBC to run them and process the results. JDBC has evolved into a rich and flexible database communication library, which now provides ways to simplify and improve on this approach, but there is still a fair degree of tedium involved. People who work with data a great deal need more power, some way of moving the queries out of the code, and making them act more like well-behaved components in an object-oriented world.

Such capabilities have been part ...