What could cause a MappingException to be thrown after upgrading Hibernate from 4.3.11.Final to 5.1.0.Final?

Question

Java

What are the significant changes in 5.1.0.Final that might cause hibernate.xfg.xml mappings to not work? With version 4.3.11.Final everything works fine.
When I try to save an object to the database, I get an exception:

Exception in thread "main" org.hibernate.MappingException: Unknown entity: test.hibernate.Book
  at org.hibernate.internal.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:776)
  at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1533)
  at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:104)
  at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:192)
  at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:38)
  at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:177)
  at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:32)
  at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
  at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:682)
  at org.hibernate.internal.SessionImpl.save(SessionImpl.java:674)
  at org.hibernate.internal.SessionImpl.save(SessionImpl.java:669)
  at test.hibernate.Main.main(Main.java:26)

main():

// Configure Hibernate and build session factory
Configuration configuration = new Configuration().configure();
ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
    .applySettings(configuration.getProperties()).build();
SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
// Save a book object
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Book book = new Book();
book.setName("qwerty");
session.save(book);
transaction.commit();
session.close();

hibernate.cfg.xml:

<hibernate-configuration>
  <session-factory>
    <property name="connection.driver_class">org.h2.Driver</property>
    <property name="connection.url">jdbc:h2:mem:test_db</property>
    <property name="connection.username"></property>
    <property name="connection.password"></property>
    <property name="dialect">org.hibernate.dialect.H2Dialect</property>
    <property name="show_sql">true</property>
    <property name="hbm2ddl.auto">create-drop</property>
    <property name="hibernate.current_session_context_class">thread</property>
    <mapping class="test.hibernate.Book" />
  </session-factory>
</hibernate-configuration>

test.hibernate.Book:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "books")
public class Book {
  @Id
  @GeneratedValue
  private int id;
  @Column(nullable = false, length = 100, unique = true)
  private String name;
  // Getters & setters...
}

Answer 1

To initialize the SessionFactory you need this:

Configuration configuration = new Configuration().configure();
ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
    .applySettings(configuration.getProperties()).build();
SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);

replace with this:
Discussed here: stackoverflow.com/questions/32405031/hibernate-5-o...