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// $Id: Persistence.java 14134 2007-10-25 22:34:46Z epbernard $
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package javax.persistence;
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import java.io.BufferedReader;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.net.URL;
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import java.util.Enumeration;
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import java.util.HashSet;
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import java.util.Map;
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import java.util.Set;
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import java.util.regex.Matcher;
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import java.util.regex.Pattern;
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import javax.persistence.spi.PersistenceProvider;
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/**
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 * Bootstrap class that provides access to an EntityManagerFactory.
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 */
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public class Persistence {
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        //typo intended because it leaked into the JPA 1 spec. Do not use this constant.
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        public static final java.lang.String PERSISTENCE_PROVIDER = "javax.persistence.spi.PeristenceProvider";
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        protected static final Set<PersistenceProvider> providers = new HashSet<PersistenceProvider>();
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        /**
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         * Create and return an EntityManagerFactory for the named persistence unit.
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         *
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         * @param persistenceUnitName The name of the persistence unit
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         * @return The factory that creates EntityManagers configured according to the specified persistence unit
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         */
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        public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName) {
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                return createEntityManagerFactory( persistenceUnitName, null );
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        }
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        /**
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         * Create and return an EntityManagerFactory for the named persistence unit using the given properties.
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         *
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         * @param persistenceUnitName The name of the persistence unit
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         * @param properties Additional properties to use when creating the factory. The values of these properties override
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         * any values that may have been configured elsewhere
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         * @return The factory that creates EntityManagers configured according to the specified persistence unit
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         */
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        public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName, Map properties) {
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                EntityManagerFactory emf = null;
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                if ( providers.size() == 0 ) {
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                        findAllProviders();
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                }
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                for ( PersistenceProvider provider : providers ) {
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                        emf = provider.createEntityManagerFactory( persistenceUnitName, properties );
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                        if ( emf != null ) break;
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                }
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                if ( emf == null ) {
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                        throw new PersistenceException( "No Persistence provider for EntityManager named " + persistenceUnitName );
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                }
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                return emf;
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        }
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        // Helper methods
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        private static void findAllProviders() {
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                try {
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                        ClassLoader loader = Thread.currentThread().getContextClassLoader();
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                        Enumeration<URL> resources = loader.getResources( "META-INF/services/" + PersistenceProvider.class.getName() );
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                        Set<String> names = new HashSet<String>();
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                        while ( resources.hasMoreElements() ) {
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                                URL url = resources.nextElement();
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                                InputStream is = url.openStream();
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                                try {
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                                        names.addAll( providerNamesFromReader( new BufferedReader( new InputStreamReader( is ) ) ) );
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                                }
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                                finally {
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                                        is.close();
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                                }
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                        }
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                        for ( String s : names ) {
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                                Class providerClass = loader.loadClass( s );
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                                providers.add( (PersistenceProvider) providerClass.newInstance() );
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                        }
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                }
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                catch (IOException e) {
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                        throw new PersistenceException( e );
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                }
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                catch (InstantiationException e) {
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                        throw new PersistenceException( e );
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                }
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                catch (IllegalAccessException e) {
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                        throw new PersistenceException( e );
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                }
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                catch (ClassNotFoundException e) {
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                        throw new PersistenceException( e );
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                }
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        }
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        private static final Pattern nonCommentPattern = Pattern.compile( "^([^#]+)" );
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        private static Set<String> providerNamesFromReader(BufferedReader reader) throws IOException {
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                Set<String> names = new HashSet<String>();
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                String line;
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                while ( ( line = reader.readLine() ) != null ) {
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                        line = line.trim();
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                        Matcher m = nonCommentPattern.matcher( line );
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                        if ( m.find() ) {
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                                names.add( m.group().trim() );
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                        }
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                }
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                return names;
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        }
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}