<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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">
  <persistence-unit name="persistenceUnit" transaction-type="JTA">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <jta-data-source>java:jboss/datasources/myds</jta-data-source>
    <class>com.app.entity,MyEntity</class>
    <properties>
      <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
      <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
      <property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.ImprovedNamingStrategy"/>
      <property name="hibernate.connection.charSet" value="UTF-8"/>
      <property name="hibernate.validator.apply_to_ddl" value="false"/>
      <property name="hibernate.validator.autoregister_listeners" value="false"/>
    </properties>
  </persistence-unit>
</persistence>

    @PersistenceContext
    private EntityManager entityManager;    
    
    @Override
    public void save(MyEntity ent) {
        if (entityManager == null) System.out.println("!!!!!!!!!!!!!!!!!!!!! ENTITY MANAGER IS NULL !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
        else System.out.println("!!!!!!!!!!!!!!!!!!!!! ENTITY MANAGER IS NOT NULL !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
    }