import org.eclipse.persistence.config.PersistenceUnitProperties;
import org.eclipse.persistence.internal.jpa.EntityManagerImpl;
import org.eclipse.persistence.sessions.coordination.MetadataRefreshListener;
import org.eclipse.persistence.sessions.server.ServerSession;
import org.springframework.orm.jpa.JpaTransactionManager;
import sk.bantip.hotel.server.security.SecurityHelper;

import javax.persistence.EntityManager;
import java.util.HashMap;
import java.util.Map;

public class MultiTenantJpaTransactionManager extends JpaTransactionManager {

    /**
     * NOTE:
     * Maybe it would be also possible to replace existing entityManager in transaction with new but it
     * isn't a good idea because of rollback and other problems.
     * So when new tenant is required always start new transaction for it.
     */

    @Override
    protected javax.persistence.EntityManager createEntityManagerForTransaction() {
        EntityManager em = super.createEntityManagerForTransaction();

        boolean refreshed = false;
        String actualTenant = null;
        ServerSession ss = ((EntityManagerImpl) em.getDelegate()).getServerSession();
        Map sessionProp = ss.getProperties();
        actualTenant = (String) sessionProp.get(PersistenceUnitProperties.MULTITENANT_PROPERTY_DEFAULT);
        // don't run it if tenant didn't change
        // it should be quite faster then
        if ((actualTenant == null && SecurityHelper.getActiveTenantSchema() != null) ||
                (actualTenant != null  && !actualTenant.equals(SecurityHelper.getActiveTenantSchema()))) {
            // set new tenant as property for actual session
            // while refreshing metadata it will be used from actual session for new session
            sessionProp.put(PersistenceUnitProperties.MULTITENANT_PROPERTY_DEFAULT, SecurityHelper.getActiveTenantSchema());
            MetadataRefreshListener mrl = ((EntityManagerImpl) em.getDelegate()).getServerSession().getRefreshMetadataListener();
            // metadata refresh listener is empty if it was already run for actual transaction (same entity manager)
            // because it is placed in createEntityManagerForTransaction now this shouldn't happen but to be sure...
            if (mrl != null) {
                Map<String, Object> prop = new HashMap<String, Object>();
                // metadata will be refreshed for next created entity manager
                mrl.triggerMetadataRefresh(prop);
                refreshed = true;
            }
        }

        // if metadata for "old" entity manager wasn't refreshed we don't need to create a new one
        return refreshed ? super.createEntityManagerForTransaction() : em;
    }
}

import org.eclipse.persistence.annotations.TenantTableDiscriminatorType;
import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.descriptors.TablePerMultitenantPolicy;

/**
 * For some reason when using table per tenant with schema discriminator isn't set good for child
 * entities with inheritance JOINED strategy. It stay as SUFFIX and therefore it doesn't work.
 */
public class InheritanceJoinedMTFixCustomizer implements DescriptorCustomizer {

    @Override
    public void customize(ClassDescriptor descriptor) throws Exception {
        // set discriminator to SCHEMA
        ((TablePerMultitenantPolicy) descriptor.getMultitenantPolicy())
                .setTenantTableDiscriminatorType(TenantTableDiscriminatorType.SCHEMA);
    }
}

...
@Customizer(InheritanceJoinedMTFixCustomizer.class)
public class Person extends Contact {
...

org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is javax.persistence.PersistenceException: Exception [EclipseLink-28013] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException Exception Description: Unable to deploy PersistenceUnit ###### in invalid state [DeployFailed]. Internal Exception: javax.persistence.PersistenceException: Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException Exception Description: Deployment of PersistenceUnit ###### failed. Close all factories for this PersistenceUnit. Internal Exception: javax.persistence.PersistenceException: Exception [EclipseLink-28009] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException Exception Description: Attempted to redeploy a session named file: ####### without closing it.

public class MultiTenantJpaTransactionManager extends JpaTransactionManager {

  /**
   * This process shouldn't be interrupted by concurrent thread.
   * Therefore the method is synchronized.
   */
  @Override
  protected synchronized EntityManager createEntityManagerForTransaction() {
    EntityManager em = null;
    Map<String, Object> properties = getJpaPropertyMap();
    // get EMF from JpaTransactionManager
    EntityManagerFactory emf = ((EntityManagerFactoryInfo) getEntityManagerFactory()).getNativeEntityManagerFactory();
    boolean isMetadataExpired = ((EntityManagerFactoryImpl) emf).unwrap().getSetupImpl().isMetadataExpired();
    // it is needed to get EM to update metadata if they are marked as expired otherwise serverSesstion and
    // therefore also actualTenant value being get below wouldn't be actual
    if (isMetadataExpired) {
      em = (!CollectionUtils.isEmpty(properties) ?
           emf.createEntityManager(properties) : emf.createEntityManager());
    }
    Server ss = JpaHelper.getServerSession(emf);
    String actualTenant = (String) ss.getProperty(PersistenceUnitProperties.MULTITENANT_PROPERTY_DEFAULT);
    // don't run it if tenant didn't change
    // it should be quite faster then
    if ((actualTenant == null && SecurityHelper.getActiveTenantSchema() != null) ||
        (actualTenant != null  && !actualTenant.equals(SecurityHelper.getActiveTenantSchema()))) {
      Map newProperties = new HashMap();
      newProperties.put(PersistenceUnitProperties.MULTITENANT_PROPERTY_DEFAULT, SecurityHelper.getActiveTenantSchema());
      JpaHelper.getEntityManagerFactory(emf).refreshMetadata(newProperties);
    } else
    if (em != null) {
      // don't get it again
      // it is unnecessary
      return em;
    }

    return (!CollectionUtils.isEmpty(properties) ? emf.createEntityManager(properties) : emf.createEntityManager());
  }
}