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 *     https://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
037    /** Stores a map with the registered public IDs. */
038    private final Map<String, URL> registeredEntities = new HashMap<>();
039
040    /**
041     * Constructs a new instance.
042     */
043    public DefaultEntityResolver() {
044        // empty
045    }
046
047    /**
048     * Gets a map with the entity IDs that have been registered using the {@code registerEntityId()} method.
049     *
050     * @return a map with the registered entity IDs
051     */
052    @Override
053    public Map<String, URL> getRegisteredEntities() {
054        return registeredEntities;
055    }
056
057    /**
058     * <p>
059     * Registers the specified URL for the specified public identifier.
060     * </p>
061     * <p>
062     * This implementation maps {@code PUBLICID}'s to URLs (from which the resource will be loaded). A common use case for
063     * this method is to register local URLs (possibly computed at runtime by a class loader) for DTDs and Schemas. This
064     * allows the performance advantage of using a local version without having to ensure every {@code SYSTEM} URI on every
065     * processed XML document is local. This implementation provides only basic functionality. If more sophisticated
066     * features are required, either calling {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom
067     * {@code DocumentBuilder} (which also can be initialized with a custom {@code EntityResolver}) or creating a custom
068     * entity resolver and registering it with the XMLConfiguration is recommended.
069     * </p>
070     *
071     * @param publicId Public identifier of the Entity to be resolved
072     * @param entityURL The URL to use for reading this Entity
073     * @throws IllegalArgumentException if the public ID is undefined
074     */
075    @Override
076    public void registerEntityId(final String publicId, final URL entityURL) {
077        if (publicId == null) {
078            throw new IllegalArgumentException("Public ID must not be null!");
079        }
080        getRegisteredEntities().put(publicId, entityURL);
081    }
082
083    /**
084     * Resolves the requested external entity. This is the default implementation of the {@code EntityResolver} interface.
085     * It checks the passed in public ID against the registered entity IDs and uses a local URL if possible.
086     *
087     * @param publicId the public identifier of the entity being referenced
088     * @param systemId the system identifier of the entity being referenced
089     * @return an input source for the specified entity
090     * @throws org.xml.sax.SAXException if a parsing exception occurs
091     */
092    @SuppressWarnings("resource") // The stream is managed by the InputSource returned by this method.
093    @Override
094    public InputSource resolveEntity(final String publicId, final String systemId) throws SAXException {
095        // Has this system identifier been registered?
096        URL entityURL = null;
097        if (publicId != null) {
098            entityURL = getRegisteredEntities().get(publicId);
099        }
100
101        if (entityURL != null) {
102            // Obtain an InputSource for this URL. This code is based on the
103            // createInputSourceFromURL() method of Commons Digester.
104            try {
105                final URLConnection connection = entityURL.openConnection();
106                connection.setUseCaches(false);
107                final InputStream stream = connection.getInputStream();
108                final InputSource source = new InputSource(stream);
109                source.setSystemId(entityURL.toExternalForm());
110                return source;
111            } catch (final IOException e) {
112                throw new SAXException(e);
113            }
114        }
115        // default processing behavior
116        return null;
117    }
118}