Dynamic properties inside persistence.xml

EnvironmentSpecificHibernatePersistence.java

import java.util.HashMap;
import java.util.Map;

import javax.persistence.EntityManagerFactory;
import javax.persistence.spi.PersistenceProvider;
import javax.persistence.spi.PersistenceUnitInfo;

import org.hibernate.ejb.Ejb3Configuration;
import org.hibernate.ejb.HibernatePersistence;

/**
 * <strong>This class does theoretically work, but not in practice. Thanks to
 * the Java EE 6 standards.</strong><br />
 * Use this {@link PersistenceProvider} if you have properties inside your
 * properties.xml that must be set inside different application server
 * environments. I wrote this class for supporting Hibernate inside JBoss and
 * WebSphere. All checked properties are retrieved through
 * {@link System#getProperty(String)}.
 * 
 * See this example persistence.xml
 * 
 * <pre>
 * &lt;persistence-unit name=&quot;Example&quot;&gt; 
 * 	&lt;!-- Use our own provider so we can manage the properties --&gt;
 * 	&lt;provider&gt;EnvironmentSpecificHibernatePersistence&lt;/provider&gt;
 * 	&lt;jta-data-source&gt;jdbc/MyJTADataSource&lt;/jta-data-source&gt;
 * 	&lt;properties&gt; 
 * 		&lt;property name=&quot;hibernate.transaction.factory_class&quot; value=&quot;org.hibernate.transaction.CMTTransactionFactory&quot;/&gt; 
 * 
 * 		&lt;!-- WebSphere specific setting; which is the default in production environment --&gt; 
 * 		&lt;property name=&quot;hibernate.transaction.manager_lookup_class&quot; value=&quot;org.hibernate.transaction.WebSphereExtendedJTATransactionLookup&quot;/&gt; 
 * 		&lt;property name=&quot;jta.UserTransaction&quot; value=&quot;java:comp/UserTransaction&quot;/&gt;
 * 
 * 		&lt;!-- JBoss specific setting; the environment variable applicationserver.runtime has been set inside JBoss --&gt;
 * 		&lt;!-- Remove the hibernate.transaction.manager_lookup_class setting --&gt;
 * 		&lt;property name=&quot;?(applicationserver.runtime=jboss)hibernate.transaction.manager_lookup_class&quot; value=&quot;&quot; /&gt;
 * 		&lt;!-- Overwrite the setting --&gt;
 * 		&lt;property name=&quot;?(applicationserver.runtime=jboss)jta.UserTransaction&quot; value=&quot;java:comp/JBossUserTransaction&quot; /&gt;
 * 	&lt;/properties&gt;
 * &lt;/persistence&gt;
 * </pre>
 * 
 * @author ckl
 * 
 */
@Deprecated
public class EnvironmentSpecificHibernatePersistence extends HibernatePersistence {
	/**
	 * Create an entity manager factory from the given persistence unit info,
	 * using the specified properties (they override any on the PUI).
	 * <p/>
	 * This is the form used by the container in a JEE environment.
	 * 
	 * @param info
	 *            The persistence unit information
	 * @param properties
	 *            The explicit property values
	 * 
	 * @return initialized EntityManagerFactory
	 */
	public EntityManagerFactory createContainerEntityManagerFactory(PersistenceUnitInfo info, Map properties) {
		Map environmentProperties = parsePropertyExpressions(properties);
		Ejb3Configuration cfg = new Ejb3Configuration();
		Ejb3Configuration configured = cfg.configure(info, properties);
		return configured != null ? configured.buildEntityManagerFactory() : null;
	}

	/**
	 * Iterates over every entry of the properties map and checks for an
	 * expression like "?($environment=value)key...". If this expression
	 * evaluates to true, any property with name "key" will be overwritten.
	 * 
	 * @param originalPersistenceXmlProperties
	 * @return
	 */
	@SuppressWarnings({ "rawtypes", "unchecked" })
	public Map parsePropertyExpressions(Map originalPersistenceXmlProperties) {
		HashMap r = new HashMap();
		HashMap overwriteLater = new HashMap();

		for (Object persistenceXmlKey : originalPersistenceXmlProperties.keySet()) {
			if (persistenceXmlKey instanceof String) {
				String key = (String) persistenceXmlKey;

				// get positions of marker characters
				int posExpressionBegin = key.indexOf("?(");
				int posExpressionEnd = key.indexOf(")");
				int posExpressionEqual = key.indexOf("=");

				// does the string match the format
				// ?($systemProperty=$value)$key
				if ((posExpressionBegin >= 0) && (posExpressionEnd > 0) && (posExpressionEqual > posExpressionBegin)
						&& (posExpressionEqual < posExpressionEnd)) {
					String systemPropertyToAssert = key.substring(posExpressionBegin + 2, posExpressionEqual);
					String systemPropertyIsValue = key.substring(posExpressionEqual + 1, posExpressionEnd);

					String valueOfSystemProperty = System.getProperty(systemPropertyToAssert);
					String evaluatedPersistenceXmlKey = key.substring(posExpressionEnd + 1);

					// is the system property defined?
					if ((valueOfSystemProperty != null) && valueOfSystemProperty.equals(systemPropertyIsValue)
							&& (evaluatedPersistenceXmlKey != null) && (evaluatedPersistenceXmlKey.length() > 0)) {
						// retrieve the value of this key from persistence.xml
						Object value = originalPersistenceXmlProperties.get(persistenceXmlKey);

						// no value passed => remove key from properties
						if (value == null || ((value instanceof String) && ((String) value).length() == 0)) {
							r.remove(evaluatedPersistenceXmlKey);
						}
						// add new property value to the pushed properties
						else {
							overwriteLater.put(evaluatedPersistenceXmlKey,
									originalPersistenceXmlProperties.get(persistenceXmlKey));
						}
					}
				}
			}

			// add every key
			r.put(persistenceXmlKey, originalPersistenceXmlProperties.get(persistenceXmlKey));
		}

		// overwrite specific keys
		r.putAll(overwriteLater);

		return r;
	}
}