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 *
033 * @since 1.7
034 */
035public class DefaultEntityResolver implements EntityResolver, EntityRegistry {
036    /** Stores a map with the registered public IDs. */
037    private final Map<String, URL> registeredEntities = new HashMap<>();
038
039    /**
040     * Gets a map with the entity IDs that have been registered using the {@code registerEntityId()} method.
041     *
042     * @return a map with the registered entity IDs
043     */
044    @Override
045    public Map<String, URL> getRegisteredEntities() {
046        return registeredEntities;
047    }
048
049    /**
050     * <p>
051     * Registers the specified URL for the specified public identifier.
052     * </p>
053     * <p>
054     * This implementation maps {@code PUBLICID}'s to URLs (from which the resource will be loaded). A common use case for
055     * this method is to register local URLs (possibly computed at runtime by a class loader) for DTDs and Schemas. This
056     * allows the performance advantage of using a local version without having to ensure every {@code SYSTEM} URI on every
057     * processed XML document is local. This implementation provides only basic functionality. If more sophisticated
058     * features are required, either calling {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom
059     * {@code DocumentBuilder} (which also can be initialized with a custom {@code EntityResolver}) or creating a custom
060     * entity resolver and registering it with the XMLConfiguration is recommended.
061     * </p>
062     *
063     * @param publicId Public identifier of the Entity to be resolved
064     * @param entityURL The URL to use for reading this Entity
065     * @throws IllegalArgumentException if the public ID is undefined
066     */
067    @Override
068    public void registerEntityId(final String publicId, final URL entityURL) {
069        if (publicId == null) {
070            throw new IllegalArgumentException("Public ID must not be null!");
071        }
072        getRegisteredEntities().put(publicId, entityURL);
073    }
074
075    /**
076     * Resolves the requested external entity. This is the default implementation of the {@code EntityResolver} interface.
077     * It checks the passed in public ID against the registered entity IDs and uses a local URL if possible.
078     *
079     * @param publicId the public identifier of the entity being referenced
080     * @param systemId the system identifier of the entity being referenced
081     * @return an input source for the specified entity
082     * @throws org.xml.sax.SAXException if a parsing exception occurs
083     */
084    @SuppressWarnings("resource") // The stream is managed by the InputSource returned by this method.
085    @Override
086    public InputSource resolveEntity(final String publicId, final String systemId) throws SAXException {
087        // Has this system identifier been registered?
088        URL entityURL = null;
089        if (publicId != null) {
090            entityURL = getRegisteredEntities().get(publicId);
091        }
092
093        if (entityURL != null) {
094            // Obtain an InputSource for this URL. This code is based on the
095            // createInputSourceFromURL() method of Commons Digester.
096            try {
097                final URLConnection connection = entityURL.openConnection();
098                connection.setUseCaches(false);
099                final InputStream stream = connection.getInputStream();
100                final InputSource source = new InputSource(stream);
101                source.setSystemId(entityURL.toExternalForm());
102                return source;
103            } catch (final IOException e) {
104                throw new SAXException(e);
105            }
106        }
107        // default processing behavior
108        return null;
109    }
110}