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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * 
 * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
 * 
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License. You can obtain
 * a copy of the License at https://glassfish.dev.java.net/public/CDDL+GPL.html
 * or glassfish/bootstrap/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 * 
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at glassfish/bootstrap/legal/LICENSE.txt.
 * Sun designates this particular file as subject to the "Classpath" exception
 * as provided by Sun in the GPL Version 2 section of the License file that
 * accompanied this code.  If applicable, add the following below the License
 * Header, with the fields enclosed by brackets [] replaced by your own
 * identifying information: "Portions Copyrighted [year]
 * [name of copyright owner]"
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 * Contributor(s):
 * 
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
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 */
package javax.persistence;

// J2SE imports
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Set;
import java.util.Map;
import java.util.HashSet;
import java.util.Enumeration;
import java.net.URL;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

// persistence imports
import javax.persistence.spi.PersistenceProvider;

/**
 * Bootstrap class that is used to obtain an {@link EntityManagerFactory}.
 *
 * @since Java Persistence 1.0
 */
public class Persistence {

    public static final String PERSISTENCE_PROVIDER = "javax.persistence.spi.PeristenceProvider";
    protected static final Set providers = new HashSet();
  
    /**
     * Create and return an EntityManagerFactory for the 
     * named persistence unit.
     * 
     * @param persistenceUnitName The name of the persistence unit
     * @return The factory that creates EntityManagers configured 
     * according to the specified persistence unit
     */
    public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName) {
        return createEntityManagerFactory(persistenceUnitName, null);
    }

    /**
     * Create and return an EntityManagerFactory for the 
     * named persistence unit using the given properties.
     * 
     * @param persistenceUnitName The name of the persistence unit
     * @param properties Additional properties to use when creating the 
     * factory. The values of these properties override any values
     * that may have been configured elsewhere.
     * @return The factory that creates EntityManagers configured 
     * according to the specified persistence unit.
     */
    public static EntityManagerFactory createEntityManagerFactory(
            String persistenceUnitName, Map properties) {
        EntityManagerFactory emf = null;
        if (providers.size() == 0) {
            try{
                findAllProviders();
            } catch (IOException exc){};
        }
        for (PersistenceProvider provider : providers) {
            emf = provider.createEntityManagerFactory(persistenceUnitName, properties);
            if (emf != null){
                break;
            }
        }
        if (emf == null) {
            throw new PersistenceException("No Persistence provider for EntityManager named " + persistenceUnitName);
        }
        return emf;
    }
  
    // Helper methods

    private static void findAllProviders() throws IOException {
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        Enumeration resources = 
            loader.getResources("META-INF/services/" + PersistenceProvider.class.getName());
        Set names = new HashSet();
        while (resources.hasMoreElements()) {
            URL url = resources.nextElement();
            InputStream is = url.openStream();
            try {
                names.addAll(providerNamesFromReader(new BufferedReader(new InputStreamReader(is))));
            } finally {
                is.close();
            }
        }
        for (String s : names) {
            try{
                providers.add((PersistenceProvider)loader.loadClass(s).newInstance());
            } catch (ClassNotFoundException exc){
            } catch (InstantiationException exc){
            } catch (IllegalAccessException exc){
            }
        }
    }

    private static final Pattern nonCommentPattern = Pattern.compile("^([^#]+)");

    private static Set providerNamesFromReader(BufferedReader reader) throws IOException {
        Set names = new HashSet();
        String line;
        while ((line = reader.readLine()) != null) {
            line = line.trim();
            Matcher m = nonCommentPattern.matcher(line);
            if (m.find()) {
                names.add(m.group().trim());
            }
        }
        return names;
    }
}