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     */
017    package org.apache.commons.configuration.resolver;
018    
019    import org.xml.sax.InputSource;
020    import org.xml.sax.SAXException;
021    import org.xml.sax.EntityResolver;
022    
023    import java.net.URL;
024    import java.net.URLConnection;
025    import java.io.InputStream;
026    import java.io.IOException;
027    import java.util.Map;
028    import java.util.HashMap;
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 729581 2008-12-27 02:27:49Z rgoers $
037     */
038    public class DefaultEntityResolver implements EntityResolver, EntityRegistry
039    {
040        /** Stores a map with the registered public IDs.*/
041        private Map registeredEntities = new HashMap();
042    
043        /**
044         * <p>
045         * Registers the specified URL for the specified public identifier.
046         * </p>
047         * <p>
048         * This implementation maps <code>PUBLICID</code>'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</code> 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)<code> to set a custom
056         * <code>DocumentBuilder</code> (which also can be initialized with a
057         * custom <code>EntityResolver</code>) 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</code> 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 = (URL) 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()</code> method.
123         *
124         * @return a map with the registered entity IDs
125         */
126        public Map getRegisteredEntities()
127        {
128            return registeredEntities;
129        }
130    }