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.configuration.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 * @version $Id: DefaultEntityResolver.java 1301991 2012-03-17 20:18:02Z sebb $
037 */
038public class DefaultEntityResolver implements EntityResolver, EntityRegistry
039{
040    /** Stores a map with the registered public IDs.*/
041    private Map<String, URL> registeredEntities = new HashMap<String, URL>();
042
043    /**
044     * <p>
045     * Registers the specified URL for the specified public identifier.
046     * </p>
047     * <p>
048     * This implementation maps {@code PUBLICID}'s to URLs (from which
049     * the resource will be loaded). A common use case for this method is to
050     * register local URLs (possibly computed at runtime by a class loader) for
051     * DTDs and Schemas. This allows the performance advantage of using a local
052     * version without having to ensure every {@code SYSTEM} URI on every
053     * processed XML document is local. This implementation provides only basic
054     * functionality. If more sophisticated features are required, either calling
055     * {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom
056     * {@code DocumentBuilder} (which also can be initialized with a
057     * custom {@code EntityResolver}) or creating a custom entity resolver
058     * and registering it with the XMLConfiguration is recommended.
059     * </p>
060     *
061     * @param publicId Public identifier of the Entity to be resolved
062     * @param entityURL The URL to use for reading this Entity
063     * @throws IllegalArgumentException if the public ID is undefined
064     */
065    public void registerEntityId(String publicId, 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    public InputSource resolveEntity(String publicId, String systemId)
086            throws SAXException
087    {
088        // Has this system identifier been registered?
089        URL entityURL = null;
090        if (publicId != null)
091        {
092            entityURL = getRegisteredEntities().get(publicId);
093        }
094
095        if (entityURL != null)
096        {
097            // Obtain an InputSource for this URL. This code is based on the
098            // createInputSourceFromURL() method of Commons Digester.
099            try
100            {
101                URLConnection connection = entityURL.openConnection();
102                connection.setUseCaches(false);
103                InputStream stream = connection.getInputStream();
104                InputSource source = new InputSource(stream);
105                source.setSystemId(entityURL.toExternalForm());
106                return source;
107            }
108            catch (IOException e)
109            {
110                throw new SAXException(e);
111            }
112        }
113        else
114        {
115            // default processing behavior
116            return null;
117        }
118    }
119
120    /**
121     * Returns a map with the entity IDs that have been registered using the
122     * {@code registerEntityId()} method.
123     *
124     * @return a map with the registered entity IDs
125     */
126    public Map<String, URL> getRegisteredEntities()
127    {
128        return registeredEntities;
129    }
130}