How do you programmatically generate a Hibernate JPA schema?

Question

I\'d like to use the Hibernate/HBM2DDL schema generation as a starting point for managing my application\'s SQL schema using a tool like Liquibase or Flyway. To assist with

Answer 1

After digging through the Hibernate Ant task's source on GitHub, I came up with the following solution:

/**
 * Uses Hibernate's HBM2DDL {@link SchemaExport} utility to generate SQL
 * database schemas.
 */
public final class HibernateSchemaPrinter {
    /**
     * A small application driver that calls
     * {@link #printHibernateSchemaToStdout(String, Class)}.
     * 
     * @param args
     *            (unused)
     */
    public static void main(String[] args) {
        printHibernateSchemaToStdout("gov.hhs.cms.bluebutton.data", PostgreSQL95Dialect.class);
    }

    /**
     * Prints the Hibernate-/HDM2DDL- auto-generated SQL schema to
     * {@link System#out}.
     * 
     * @param persistenceUnitName
     *            the name of the JPA persistence unit to generate the schema
     *            for
     * @param dialectType
     *            the Hibernate {@link Dialect} type to generate the schema for,
     *            e.g. {@link PostgreSQL95Dialect}
     */
    public static void printHibernateSchemaToStdout(String persistenceUnitName, Class dialectType) {
        Map properties = new HashMap<>();
        properties.put(AvailableSettings.DIALECT, dialectType.getName());

        /*
         * Use a Hibernate EntityManagerFactoryBuilderImpl to create a JPA
         * EntityManagerFactory, then grab the (now populated) Hibernate
         * Metadata instance out of it.
         */
        EntityManagerFactoryBuilderImpl entityManagerFactoryBuilder = new CustomHibernatePersistenceProvider()
                .getEntityManagerFactoryBuilder(persistenceUnitName, properties);
        entityManagerFactoryBuilder.build();
        Metadata metadata = entityManagerFactoryBuilder.getMetadata();

        SchemaExport schemaExport = new SchemaExport();
        schemaExport.setHaltOnError(true);
        schemaExport.setFormat(true);
        schemaExport.setDelimiter(";");
        schemaExport.execute(EnumSet.of(TargetType.STDOUT), Action.CREATE, metadata);
    }

    /**
     * A small hack, needed to extract the
     * {@link EntityManagerFactoryBuilderImpl} from
     * {@link HibernatePersistenceProvider}. Taken from the Hibernate Ant task
     * here: 
     * JPAConfigurationTask.java.
     */
    private static final class CustomHibernatePersistenceProvider extends HibernatePersistenceProvider {
        /**
         * (See overridden method; we're just making it public.)
         * 
         * @param persistenceUnit
         *            (see overridden method)
         * @param properties
         *            (see overridden method)
         * @return (see overridden method)
         */
        public EntityManagerFactoryBuilderImpl getEntityManagerFactoryBuilder(String persistenceUnit,
                Map properties) {
            return (EntityManagerFactoryBuilderImpl) getEntityManagerFactoryBuilderOrNull(persistenceUnit, properties);
        }
    }
}

Takes a bit more code these days, but still works, so good enough.