Location of the persistence.xml in a Java Client App

Question

I am a newbie in Hibernate. In order to get the transaction by the EntityManager, I need to use EntityManager Factory. When I put this code block on my file:

EntityManagerFactory entityManagerFactory = Persistence
            .createEntityManagerFactory("Comment");

EntityManager entityManager = entityManagerFactory.createEntityManager();

EntityTransaction transaction = entityManager.getTransaction();

transaction.begin();
entityManager.persist(obj);
transaction.commit();

I got this Exception:

javax.persistence.PersistenceException: No Persistence provider for EntityManager named Comment

Then I realized that I need to add a persistence.xml file:

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
  <persistence-unit name="QuestionsComments" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>Comment</class>
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLInnoDBDialect"/>
      <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
      <property name="hibernate.show_sql" value="true"/>
      <property name="hibernate.connection.username" value="root"/>
      <property name="hibernate.connection.password" value="root"/>
      <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/sogdb"/>
      <property name="hibernate.max_fetch_depth" value="3"/>
    </properties>
  </persistence-unit>
</persistence>

Actually, The app I am using is not a Java on Server app (I have a Client app). Which means that there is no META-INF folder that will contain the persistence.xml file.

My Questions are:

1- Where I need to put the persistence.xml file?

2- Is the code below OK? Knowing that my table in the database is QuestionsComments and my class that will be related to it using Hibernate is Comment.

Answer 1

If you are using Eclipse, adding the JPA facet to your project allows Eclipse to take care of setting these things up for you. It will create the META-INF folder, and can generate a stub persistence.xml file in it. You don't have to be running the code on a server to have a META-INF folder in your jar file.

When you are creating the EntityManagerFactory the string argument should be the name of the persistence unit. I'd recommend using annotations in your entity class for specifying table name, id column, etc.

Edit: fixed link.

Answer 2

1. Answered clearly in this section of the Hibernate JPA Quick Start Guide. It goes in META-INF.

2. Check out the same guide just linked.

Personally I prefer the Hibernate-specific configuration hibernate.cfg.xml with annotations for mappings and Hibernate's SessionFactory for transaction access; I find it easier to wrap my head around -- although that's probably because I originally learned how to use Hibernate without knowing how to use JPA.