001/*
002 * HA-JDBC: High-Availability JDBC
003 * Copyright (c) 2004-2007 Paul Ferraro
004 * 
005 * This library is free software; you can redistribute it and/or modify it 
006 * under the terms of the GNU Lesser General Public License as published by the 
007 * Free Software Foundation; either version 2.1 of the License, or (at your 
008 * option) any later version.
009 * 
010 * This library is distributed in the hope that it will be useful, but WITHOUT
011 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
012 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License 
013 * for more details.
014 * 
015 * You should have received a copy of the GNU Lesser General Public License
016 * along with this library; if not, write to the Free Software Foundation, 
017 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
018 * 
019 * Contact: ferraro@users.sourceforge.net
020 */
021package net.sf.hajdbc.cache;
022
023import java.lang.ref.Reference;
024import java.lang.ref.SoftReference;
025import java.sql.Connection;
026import java.sql.SQLException;
027
028import net.sf.hajdbc.DatabaseProperties;
029import net.sf.hajdbc.Dialect;
030
031
032/**
033 * DatabaseMetaDataCache implementation that lazily caches data when requested.
034 * Used when a compromise between memory usage and performance is desired.
035 * Caches DatabaseProperties using a soft reference to prevent <code>OutOfMemoryError</code>s.
036 * 
037 * @author Paul Ferraro
038 * @since 2.0
039 */
040public class LazyDatabaseMetaDataCache extends AbstractDatabaseMetaDataCache
041{
042        private volatile Reference<LazyDatabaseProperties> propertiesRef = new SoftReference<LazyDatabaseProperties>(null);
043        
044        public LazyDatabaseMetaDataCache(Dialect dialect)
045        {
046                super(dialect);
047        }
048        
049        /**
050         * @see net.sf.hajdbc.DatabaseMetaDataCache#flush()
051         */
052        @Override
053        public void flush()
054        {
055                this.propertiesRef.clear();
056        }
057
058        /**
059         * @see net.sf.hajdbc.DatabaseMetaDataCache#getDatabaseProperties(java.sql.Connection)
060         */
061        @Override
062        public synchronized DatabaseProperties getDatabaseProperties(Connection connection) throws SQLException
063        {
064                LazyDatabaseProperties properties = this.propertiesRef.get();
065                
066                if (properties == null)
067                {
068                        properties = new LazyDatabaseProperties(connection.getMetaData(), new DatabaseMetaDataSupportFactoryImpl(), this.dialect);
069                
070                        this.propertiesRef = new SoftReference<LazyDatabaseProperties>(properties);
071                }
072                else
073                {
074                        properties.setConnection(connection);
075                }
076                
077                return properties;
078        }
079}