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SilverTunnel-NG Netlib is a free library for the Java programming language that implements and encapsulates all the complex network protocol stuff needed for anonymous communication over the Tor anonymity network. Netlib can be easily integrated in almost every existing and new Java application. The library requires Java 1.6/Java SE 6 or a newer version. The original silvertunnel Netlib can be found here : silvertunnel.org

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/*
 * silvertunnel.org Netlib - Java library to easily access anonymity networks
 * Copyright (c) 2009-2012 silvertunnel.org
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see .
 */
/*
 * silvertunnel-ng.org Netlib - Java library to easily access anonymity networks
 * Copyright (c) 2013 silvertunnel-ng.org
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see .
 */

package org.silvertunnel_ng.netlib.api;

import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Manage a repository of NetLayer objects.
 * 
 * @author hapke
 * @author Tobias Boese
 */
public class NetFactory implements NetLayerFactory
{
	/** */
	private static final Logger LOG = LoggerFactory.getLogger(NetFactory.class);

	public static final String NETFACTORY_MAPPING_PROPERTIES = "/org/silvertunnel_ng/netlib/api/netfactory_mapping.properties";

	/** repository cache. */
	private final Map netLayerRepository = new HashMap();

	private static NetFactory instance = new NetFactory();

	public static NetFactory getInstance()
	{
		return instance;
	}

	/**
	 * Registering a {@link NetLayer}.
	 * 
	 * @param netLayerId a {@link NetLayerIDs}
	 * @param netLayer the {@link NetLayer} to be registered
	 */
	public final synchronized void registerNetLayer(final NetLayerIDs netLayerId, final NetLayer netLayer)
	{
		netLayerRepository.put(netLayerId, netLayer);
		LOG.debug("registerNetLayer with netLayerId={}", netLayerId);
	}

	/**
	 * Cleanup all registered NetLayers.
	 */
	public final synchronized void clearRegisteredNetLayers()
	{
		netLayerRepository.clear();
	}
	/**
	 * @see NetLayerFactory#getNetLayerById(org.silvertunnel_ng.netlib.api.NetLayerIDs)
	 */
	@Override
	public synchronized NetLayer getNetLayerById(final NetLayerIDs netLayerId)
	{
		NetLayer result = netLayerRepository.get(netLayerId);
		if (result == null)
		{
			// not yet in cache: try to instantiate
			try
			{
				final NetLayerFactory factory = getNetLayerFactoryByNetLayerID(netLayerId);
				if (factory != null)
				{
					result = factory.getNetLayerById(netLayerId);
					if (result != null)
					{
						// store in cache
						registerNetLayer(netLayerId, result);
					}
				}

			}
			catch (final Exception e)
			{
				LOG.error("could not create NetLayer of {}", netLayerId, e);
			}
		}

		return result;
	}

	/**
	 * Load class based on mapping properties.
	 * 
	 * @param netLayerId
	 * @return null if not found
	 */
	private NetLayerFactory getNetLayerFactoryByNetLayerID(final NetLayerIDs netLayerId)
	{
		try
		{
			// load properties, read class factory name
			final InputStream in = getClass().getResourceAsStream(NETFACTORY_MAPPING_PROPERTIES);
			final Properties mapping = new Properties();
			mapping.load(in);

			final String netLayerFactoryClassName = mapping.getProperty(netLayerId.getValue());

			// try to load NetLayerFactory
			final Class clazz = Class.forName(netLayerFactoryClassName);
			final Constructor c = clazz.getConstructor();
			final NetLayerFactory result = (NetLayerFactory) c.newInstance();

			return result;

		}
		catch (final Exception e)
		{
			LOG.error("could not create NetLayerFactory of {}", netLayerId, e);
			return null;
		}
	}
}