How do I do JPA Batches (Insert) in EclipseLink

I want do use JPA Batches in my code.

I am using this Dependencies:

        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>eclipselink</artifactId>
            <version>2.5.1</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>javax.persistence</artifactId>
            <version>2.1.0-RC1</version>
        </dependency>

Do I have to add sth in my persistence.xml file? If yes, what do I have to add?

This is how I wrte the Jobs in my DB at the moment:

    public void writeAllJobs(List<Jobs> jobs) {

        final EntityManager em = factory.createEntityManager();

        em.getTransaction().begin();

        int counter= 0;

        for (final Job j : jobs) {

            if (counter++ >= 100) {
                em.getTransaction().commit();
                em.getTransaction().begin();
                counter = 0;
            }

            final Job job = new Job();
            job.setJobkey(j.getJobkey());
            job.setDescription(b.getDescription());
            em.persist(job);
        }
        em.getTransaction().commit();

        em.close();
    }

After 100 Joby my program wirtes the values in the DB so that is not every time a DB access.

------------------------------ EDIT -----------------------------------

    public void writeAllJobs(List<Jobs> jobs) throws SQLException {

        final EntityManager em = factory.createEntityManager();
        final java.sql.Connection connection = em.unwrap(java.sql.Connection.class);

        final String compiledQuery = "INSERT INTO JOB(JOBKEY ,DESCRIPTION)" + " VALUES" + "(?, ?)";
        final PreparedStatement preparedStatement = connection.prepareStatement(compiledQuery);

        for (final Job j : jobs) {
            preparedStatement.setInt(1, j.getJobkey());
            preparedStatement.setString(2, j.getDescription());

            preparedStatement.addBatch();
        }

        preparedStatement.executeBatch();

        connection.close();
    }

Then I get the: java.lang.NullPointerException

------------------------------ EDIT 2 -----------------------------------

I got the NPE in the line
final java.sql.Connection connection = em.unwrap(java.sql.Connection.class);

But how do I solve this problem?

You can unwrap the EntityManager to a java.sql.Connection: java.sql.Connection connection = em.unwrap(java.sql.Connection.class);

Then you can use PreparedStatements as in this answer: Efficient way to do batch INSERTS with JDBC