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