EntityManager em = entityManagerFactory.createEntityManager();
em.getTransaction().begin();
.....
EntityTransaction tx = em.getTransaction();
tx.commit();
}finally{
em.close();
}

   <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_2_0.xsd"
        version="2.0">


        <persistence-unit name="main">
                <provider>org.hibernate.ejb.HibernatePersistence</provider>

                <properties>
                        <!-- Change this to create to have Hibernate clean up after the test or
                                create-drop to keep the results after the test is done -->
                        <property name="hibernate.hbm2ddl.auto" value="update" />

                        <property name="hibernate.query.factory_class"
                                value="org.hibernate.hql.ast.ASTQueryTranslatorFactory" />
                        <property name="hibernate.cache.provider_class" value="org.hibernate.cache.HashtableCacheProvider" />
                        <property name="hibernate.archive.autodetection" value="class" />
                        <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
<property name="hibernate.connection.datasource" value="java:comp/env/jdbc/idotest"/>
                </properties>

        </persistence-unit>

public class Sender extends TimerTask {
   private static EntityManager em;
   private static EntityManagerFactory factory;

        public void run() {
                em = factory.createEntityManager();
                EntityTransaction tx = em.getTransaction();
                try
      {
         tx.begin();
                        /* Query db and do email sending work here */
         tx.commit();
      }catch(Exception ex)
      {
         if(tx.isActive())
         {
            tx.rollback();
         }
      }      
      finally
      {
         em.close();
      }                       
        }
}