001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.resolver;
018
019import java.io.IOException;
020import java.io.InputStream;
021import java.net.URL;
022import java.net.URLConnection;
023import java.util.HashMap;
024import java.util.Map;
025
026import org.xml.sax.EntityResolver;
027import org.xml.sax.InputSource;
028import org.xml.sax.SAXException;
029
030/**
031 * The DefaultEntityResolver used by XML Configurations.
032 * @author <a
033 * href="http://commons.apache.org/configuration/team-list.html">Commons
034 * Configuration team</a>
035 * @since 1.7
036 */
037public class DefaultEntityResolver implements EntityResolver, EntityRegistry
038{
039    /** Stores a map with the registered public IDs.*/
040    private final Map<String, URL> registeredEntities = new HashMap<>();
041
042    /**
043     * <p>
044     * Registers the specified URL for the specified public identifier.
045     * </p>
046     * <p>
047     * This implementation maps {@code PUBLICID}'s to URLs (from which
048     * the resource will be loaded). A common use case for this method is to
049     * register local URLs (possibly computed at runtime by a class loader) for
050     * DTDs and Schemas. This allows the performance advantage of using a local
051     * version without having to ensure every {@code SYSTEM} URI on every
052     * processed XML document is local. This implementation provides only basic
053     * functionality. If more sophisticated features are required, either calling
054     * {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom
055     * {@code DocumentBuilder} (which also can be initialized with a
056     * custom {@code EntityResolver}) or creating a custom entity resolver
057     * and registering it with the XMLConfiguration is recommended.
058     * </p>
059     *
060     * @param publicId Public identifier of the Entity to be resolved
061     * @param entityURL The URL to use for reading this Entity
062     * @throws IllegalArgumentException if the public ID is undefined
063     */
064    @Override
065    public void registerEntityId(final String publicId, final URL entityURL)
066    {
067        if (publicId == null)
068        {
069            throw new IllegalArgumentException("Public ID must not be null!");
070        }
071        getRegisteredEntities().put(publicId, entityURL);
072    }
073
074    /**
075     * Resolves the requested external entity. This is the default
076     * implementation of the {@code EntityResolver} interface. It checks
077     * the passed in public ID against the registered entity IDs and uses a
078     * local URL if possible.
079     *
080     * @param publicId the public identifier of the entity being referenced
081     * @param systemId the system identifier of the entity being referenced
082     * @return an input source for the specified entity
083     * @throws org.xml.sax.SAXException if a parsing exception occurs
084     */
085    @Override
086    public InputSource resolveEntity(final String publicId, final String systemId)
087            throws SAXException
088    {
089        // Has this system identifier been registered?
090        URL entityURL = null;
091        if (publicId != null)
092        {
093            entityURL = getRegisteredEntities().get(publicId);
094        }
095
096        if (entityURL != null)
097        {
098            // Obtain an InputSource for this URL. This code is based on the
099            // createInputSourceFromURL() method of Commons Digester.
100            try
101            {
102                final URLConnection connection = entityURL.openConnection();
103                connection.setUseCaches(false);
104                final InputStream stream = connection.getInputStream();
105                final InputSource source = new InputSource(stream);
106                source.setSystemId(entityURL.toExternalForm());
107                return source;
108            }
109            catch (final IOException e)
110            {
111                throw new SAXException(e);
112            }
113        }
114        // default processing behavior
115        return null;
116    }
117
118    /**
119     * Returns a map with the entity IDs that have been registered using the
120     * {@code registerEntityId()} method.
121     *
122     * @return a map with the registered entity IDs
123     */
124    @Override
125    public Map<String, URL> getRegisteredEntities()
126    {
127        return registeredEntities;
128    }
129}