Harnessing Hibernate

Chapter 7. The Annotations Alternative

So far, we’ve been working with the XML mapping document as the starting point for our examples. In cases where you’re starting with just a concept and can leave the details of creating data tables and data objects to Hibernate, that remains a great option. The advent of Java 5’s flexible Annotation support opened up a very interesting alternate approach, however, especially for the common case where you’ve already got some objects written by the time that you’re thinking about how to save them to a database.

Hibernate Annotations

If you haven’t started using annotations yet, the code examples in this chapter will look a little strange, so it’s worth spending a minute or two to discuss the history and purpose of Java annotations. Basically, an annotation is a way to add information about a piece of code (in the Java world, typically a class, field, or method) to help tools understand how the code is being used, or to enable automation that saves you work. Rather than having a separate file, like a persistence mapping, to maintain in parallel with your source code, you would put that information right in the source code it affected. This way you are in no danger of a file separate from your source code becoming out of synch. Before Java 5 included robust support for this style of coding, people found a “back door” way of achieving it, by leveraging the extensible nature of the JavaDoc tools.

JavaDoc was a form of annotation that existed in Java ...