title: Create JPA EntityManager without persistence.xml configuration file
body: <p>Is there a way to initialize the <code>EntityManager</code> without a persistence unit defined? Can you give all the required properties to create an entity manager? I need to create the <code>EntityManager</code> from the user's specified values at runtime. Updating the <code>persistence.xml</code> and recompiling is not an option.</p>
  
  <p>Any idea on how to do this is more than welcomed!</p>