The code generation mechanism in the Hibernate Tools consists of a few core concepts. This section explains their overall structure which are the same for the Ant and Eclipse tools.
The meta model is the model used by Hibernate core to perform its object relational mapping. The model includes information about tables, columns, classes, properties, components, values, collections etc. The API is in org.hibernate.mapping and its main entry point is the Configuration class, the same class that is used to build a session factory.
The model represented by the Configuration class can be build in many ways. The following list the currently supported ones in Hibernate Tools.
A Core configuration uses Hibernate Core and supports reading hbm.xml files, requires a hibernate.cfg.xml. Named core in Eclipse and <configuration> in ant.
A Annotation configuration uses Hibernate Annotations and supports hbm.xml and annotated classes, requires a hibernate.cfg.xml. Named annotations in Eclipse and <annotationconfiguration> in ant.
A JPA configuration uses a Hibernate EntityManager and supports hbm.xml and annotated classes requires that the project has a META-INF/persistence.xml in its classpath. Named JPA in Eclipse and <jpaconfiguration> in ant.
A JDBC configuration uses Hibernate Tools reverse engineering and reads its mappings via JDBC metadata + additional reverse engineering files (reveng.xml). Automatically used in Eclipse when doing reverse engineering from JDBC and named <jdbcconfiguration> in ant.
In most projects you will normally use only one of the Core, Annotation or JPA configuration and possibly the JDBC configuration if you are using the reverse engineering facilities of Hibernate Tools. The important thing to note is that no matter which Hibnerate Configuration type you are using Hibernate Tools supports them.
The following drawing illustrates the core concepts:
The code generation is done based on the Configuration model no matter which type of configuration have been used to create the meta model, and thus the code generation is independent on the source of the meta model and represented via Exporters.
Code generation is done in so called Exporters. An Exporter is handed a Hibernate Meta Model represented as a Configuration instance and it is then the job of the exporter to generate a set of code artifacts.
The tools provides a default set of Exporter's which can be used in both Ant and the Eclipse UI. Documentation for these Exporters is in the Ant and Eclipse sections.
Users can provide their own customer Exporter's, either by custom classes implementing the Exporter interface or simply be providing custom templates. This is documented at Section 4.4.7, “Generic Hibernate metamodel exporter (<hbmtemplate>)”