Using JNDI Resources with Hibernate

If you are using Hibernate to connect to JNDI resources on Tomcat (or an application server that manages JNDI resources the same way), this tutorial is for you!

As background, one way that Tomcat determines whether applications can access JNDI resources is by checking the context classloader. If the context classloader is a web application classloader or the child of a web application classloader, Tomcat lets it access the JNDI resources.

Although Liferay Digital Experience Platform (DXP) applications deploy on Tomcat, and DXP's classloader is a web application classloader, DXP portlet classloaders are not - the portlets are OSGi bundles installed to Liferay's OSGi container using OSGi classloaders. For a portlet to access the JNDI resources made available to the application on Tomcat, the portlet must switch to a classloader that is a child of DXP's classloader.

This tutorial demonstrates how to perform context classloader switching so that a Hibernate configuration can leverage a JNDI data source.

Note: The code demonstrated here works with Tomcat but is not guaranteed to work on other application servers. Refer to your application server's documentation for how it manages access to JNDI resources.

Environment

The code leverages improvements available since Liferay DXP SP3.

Resolution

First in your Hibernate configuration descriptor, specify a session factory that uses a JNDI data source. Here’s an abbreviated descriptor:

<?xml version="1.0"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>

        <property name="connection.datasource">java:comp/env/jdbc/mydb</property>

        <property name="current_session_context_class">thread</property>

        // Specify resources here ...
    </session-factory>
</hibernate-configuration>

If you base your descriptor on the one above, make sure to replace the connection.datasource property value with your JNDI data source name and specify resources to use in your sessions.

Next, the HibernateUtil class provides methods for creating and managing Hibernate sessions that use DXP’s classloader. Note, // Customization START/END comments mark code that lets the caller access the JNDI data source when processing the Hibernate configuration.

import com.liferay.portal.kernel.log.Log;
import com.liferay.portal.kernel.log.LogFactoryUtil;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

// Customization START
import com.liferay.portal.kernel.util.PortalClassLoaderUtil;
import com.liferay.portal.kernel.util.AggregateClassLoader;
// Customization END

public class HibernateUtil {

    public static final String COUNT_COLUMN_NAME = "COUNT_VALUE";

    public static void closeSession(Session session) {
        try {
            if ((session != null) && session.isOpen()) {
                session.close();
            }
        }
        catch (HibernateException he) {
            _log.error(he.getMessage());
        }
    }

    public static String getCountColumnName() {
        return COUNT_COLUMN_NAME;
    }

    public static SessionFactory getSessionFactory() {
        return _instance._sessionFactory;
    }

    public static Session openSession() throws HibernateException {
        return openSession(getSessionFactory());
    }

    public static Session openSession(SessionFactory sessionFactory)
        throws HibernateException {

        return sessionFactory.getCurrentSession();
    }

    private HibernateUtil() {
        // CUSTOMIZATION START

        Thread thread = Thread.currentThread();
        ClassLoader threadClassLoader = thread.getContextClassLoader();
        ClassLoader portalClassLoader = PortalClassLoaderUtil.getClassLoader();

        ClassLoader hibernateClassLoader =
            AggregateClassLoader.getAggregateClassLoader(
                portalClassLoader, threadClassLoader);

        thread.setContextClassLoader(hibernateClassLoader);

        // CUSTOMIZATION END

        try {
            Configuration configuration = new Configuration();

            configuration = configuration.configure();

            _sessionFactory = configuration.buildSessionFactory();
        }
        catch (Exception e) {
            _log.error(e, e);
        }

        // CUSTOMIZATION START

        finally {
            thread.setContextClassLoader(threadClassLoader);
        }

        // CUSTOMIZATION END
    }

    private static Log _log = LogFactoryUtil.getLog(HibernateUtil.class);

    private static HibernateUtil _instance = new HibernateUtil();

    private SessionFactory _sessionFactory;

}

Let's break down this class's logic. First, its static members are declared at the bottom.

private static Log _log = LogFactoryUtil.getLog(HibernateUtil.class);

private static HibernateUtil _instance = new HibernateUtil();

private SessionFactory _sessionFactory;

Here each member is described:

• _log: Logs messages for this class.
• _instance: the HibernateUtil instance.
• _sessionFactory: manages Hibernate sessions which, as configured, will want to have access to the JNDI resources (e.g., the JNDI data source).

The constructor HibernateUtil() makes the “magic” happen:

1. Get the current thread, its context classloader (which is an OSGi classloader), and DXP’s classloader.

   Thread thread = Thread.currentThread();
   ClassLoader threadClassLoader = thread.getContextClassLoader();
   ClassLoader portalClassLoader = PortalClassLoaderUtil.getClassLoader();
   

2. Create a new classloader that is the child of DXP’s classloader (the Portal classloader) and is able to access classes and configurations from the OSGi classloader created for your OSGi bundle. AggregateClassLoader allows us to do this without a lot of boilerplate code.

   ClassLoader hibernateClassLoader =
       AggregateClassLoader.getAggregateClassLoader(
           portalClassLoader, threadClassLoader);
   

3. Set the new classloader as the current thread’s context classloader.

   thread.setContextClassLoader(hibernateClassLoader);
   

4. Create a session factory, which loads the Hibernate configuration (the one configured earlier that uses the JNDI data source).

   try {
      Configuration configuration = new Configuration();
   
      configuration = configuration.configure();
   
      _sessionFactory = configuration.buildSessionFactory();
   }
   catch (Exception e) {
      _log.error(e, e);
   }
   

   The session factory service requests the JNDI data source, using the newly created classloader.

5. Restore the original OSGi classloader as the thread’s context classloader.

   finally {
       thread.setContextClassLoader(threadClassLoader);
   }
   

HibernateUtil’s other methods access and act on the Hibernate session factory and its sessions.

• getSessionFactory()
• closeSession(Session)
• openSession()
• openSession(SessionFactory)

Classes like HibernateUtil facilitate getting Hibernate sessions that use JNDI resources, such as JNDI data sources. You can use a version of it in your projects that use Hibernate.

Additional Information

• Connecting to JNDI Data Resources
• Configuring Dependencies