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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.envers.configuration.internal;

import org.dom4j.DocumentFactory;

import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * Small helper class that lazily loads DOM factory and keep them for fast use afterwards.
 *
 * This was part of Hibernate ORM core, but is used exclusively by Hibernate Envers now:
 * keep visibility lower so to not expose Dom4j to public API.
 * The rest of Hibernate uses StAX now for XML processing.  See {@link org.hibernate.boot.jaxb.internal.stax}
 */
final class XMLHelper {
	private final DocumentFactory documentFactory;

	XMLHelper() {
		PrivilegedAction action = new PrivilegedAction() {
			public DocumentFactory run() {
				final ClassLoader originalTccl = Thread.currentThread().getContextClassLoader();
				try {
					// We need to make sure we get DocumentFactory
					// loaded from the same ClassLoader that loads
					// Hibernate classes, to make sure we get the
					// proper version of DocumentFactory, This class
					// is "internal", and should only be used for XML
					// files generated by Envers.

					// Using the (Hibernate) ClassLoader that loads
					// this Class will avoid collisions in the case
					// that DocumentFactory can be loaded from,
					// for example, the application ClassLoader.
					Thread.currentThread().setContextClassLoader( this.getClass().getClassLoader() );
					return DocumentFactory.getInstance();
				}
				finally {
					Thread.currentThread().setContextClassLoader( originalTccl );
				}
			}
		};

		this.documentFactory = System.getSecurityManager() != null
				? AccessController.doPrivileged( action )
				: action.run();
	}

	DocumentFactory getDocumentFactory() {
		return documentFactory;
	}

}