Why is it necessary to list all of the classes/packages for the AnnotationSessionFactoryBean? Shouldn't there be a way for it to look over the classes in the classpath to discover the ones marked with @Entity?

Doing this would eliminate the need to change the XML config file every time we add a new Entity bean...

What the fuck is AnnotationSessionFactoryBean?
This is not part of hibernate's code.

Good point. I pasted the wrong class name.. it should be
org.hibernate.cfg.AnnotationConfiguration
The context of my question is using annotated entity beans under spring, however the same applies to generic hibernate annotations. (hence the AnnotationSessionFactoryBean)

Thus, why is it necessary to do the following:
sessionFactory = new AnnotationConfiguration()
.addPackage("test.animals") //the fully qualified package name
.addAnnotatedClass(Flight.class)
.addAnnotatedClass(Sky.class)
.addAnnotatedClass(Person.class)
.addAnnotatedClass(Dog.class)
.buildSessionFactory();

under spring this equivicates to:

<bean id="TestSessionFactory"
class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
<property name="dataSource" ref="dataSource" />

<property name="configurationClass">
<value>org.hibernate.cfg.AnnotationConfiguration</value>
</property>
<property name = "annotatedClasses">
<list>
<value>test.animals.Person</value>
<value>test.animals.Sky</value>
...
</list>
</property>
<property name="hibernateProperties">
<props>
<prop key="hibernate.hbm2ddl.auto">update</prop>
<prop key="hibernate.dialect">
org.hibernate.dialect.PostgreSQLDialect
</prop>
<prop key="hibernate.cache.provider_class">
org.hibernate.cache.EhCacheProvider
</prop>
<prop key="hibernate.show_sql">true</prop>
<prop key="hibernate.generate_statistics">true</prop>
</props>
</property>
</bean>

Use Hibernate EntityManager for entity autodiscovery