In java EE 6: When could I change properties on EntityManager?

Question

I want to use proxy authentication to an Oracle Express database in a simple web app with java EE 6 on Glassfish. Eclipselink 2.3.0 doc here says:

If a JEE and JTA managed EntityManager is used, specifying a proxy user/password can be more difficult, as the EntityManager and JDBC connection is not under the applications control. The persistence unit properties can still be specified on the EntityManager. As long as this is done before the EntityManager has established a database connection, this will still work.

My code is as below, but I guess the database connection is already established when the @Postconstruct init() method is called, since the last property is not changed from default true to false. Also, I get ORA-00942: table or view does not exist from the save() method. The user pool in the jdbc connection pool defined in glassfish-resources.xml has not acces to the tables, as has proxy user user_a.

@Stateless
public class Boundary {

    @PersistenceContext EntityManager em;

    @PostConstruct
    private void init()  {
        em.setProperty("eclipselink.oracle.proxy-type", OracleConnection.PROXYTYPE_USER_NAME);
        em.setProperty(OracleConnection.PROXY_USER_NAME, "pool[user_a]");
        em.setProperty(OracleConnection.PROXY_USER_PASSWORD, "pool");
        em.setProperty(OracleConnection.PROXY_ROLES, "pool_user");
        em.setProperty("eclipselink.jdbc.exclusive-connection.mode", "Always");
        em.setProperty("eclipselink.jdbc.exclusive-connection.is-lazy", "false");
    }

    public void save() {
        em.merge(new AnEntity());
    }
}

I have not much experience here, but it would be really useful if proxy authentication could be made that simple, so I spent some time trying. In a JavaEE managed context, is it possible to set properties on an EntityManager before it gets connected?

My persistence.xml:

<?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="ProxyUserPU" transaction-type="JTA">
    <jta-data-source>SecondTry</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode>
    <properties>
      <property name="eclipselink.target-database" value="Oracle"/>
      <property name="eclipselink.jdbc.exclusive-connection.is-lazy" value="true"/>
    </properties>
  </persistence-unit>
</persistence>

Answer 1

I don't think PostConstruct is the correct place for this.

A new EntityManager is bound to the persistence context on every transaction boundary, so you need to set these property at the start of every transactional SessionBean method. You could probably also use SessionEvents in EclipseLink to configure the properties.

If you properties are fixed, you could also put them in your persistence.xml.

See, http://wiki.eclipse.org/EclipseLink/Examples/JPA/Auditing#Use_Oracle_proxy_authentication_to_allow_a_shared_connection_pool_and_a_user_context