Upgrading from Hibernate 2 - Beginning Hibernate: From Novice to Professional - page 314

This is not a coincidence—in addition to the package name, there are now two versions of
the DTDs for the XML configuration files. Unchanged Hibernate 2 code should use the usual
mapping DTD reference of
http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd
And for your new Hibernate 3 code, you will use
http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd
Similarly, for the Hibernate configuration file, your version 2 code will use
http://hibernate.sourceforge.net/hibernate-configuration-2.0.dtd
And your version 3 code will use
http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd
n Caution If you do not update your mapping configuration from the Hibernate 2 form to the Hibernate 3
form, the time it takes to create a configuration and session factory will increase from around 20 seconds to
a matter of minutes.
Obviously, it will not be possible for you to have two configuration files with the same
(default) name of hibernate.cfg.xml , but either version of Hibernate permits you to con-
struct a Configuration object and then specify an explicit location for the configuration file
using the configure() methods (as shown in Listing D-1). If you are using both versions of
Hibernate simultaneously, you must make sure that POJOs are not passed from one ver-
sion's Session object to another's. If you need to persist your old POJOs using the new
version, you must update the older code to use Hibernate 3. For an explanation of how this
sort of upgrade is supported by Hibernate 3, see the description of the “classic” API in the
following section, “New Features and Support for Old Ones.”
Listing D-1. Using an Explicitly Named Configuration File in Hibernate 3
File configFile = new File("hibernate3.cfg.xml");
Configuration v3Config = new Configuration();
v3Config.configure(configFile);
SessionFactory sessionFactory =
v3Config.buildSessionFactory();
Session session = sessionFactory.openSession();
// ...
You should be aware that in your Hibernate 3 logic, some of the defaults for entries in the
mapping file have changed. If you have logic that relies upon implicit settings, you should
review your converted mapping files against the version 3 DTD to check that they will behave
as expected. The most significant change is that all mappings now default to lazy loading.