    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 * @since 1.7
    033 */
    034public class DefaultEntityResolver implements EntityResolver, EntityRegistry
    035{
    036    /** Stores a map with the registered public IDs.*/
    037    private final Map<String, URL> registeredEntities = new HashMap<>();
    038
    039    /**
    040     * <p>
    041     * Registers the specified URL for the specified public identifier.
    042     * </p>
    043     * <p>
    044     * This implementation maps {@code PUBLICID}'s to URLs (from which
    045     * the resource will be loaded). A common use case for this method is to
    046     * register local URLs (possibly computed at runtime by a class loader) for
    047     * DTDs and Schemas. This allows the performance advantage of using a local
    048     * version without having to ensure every {@code SYSTEM} URI on every
    049     * processed XML document is local. This implementation provides only basic
    050     * functionality. If more sophisticated features are required, either calling
    051     * {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom
    052     * {@code DocumentBuilder} (which also can be initialized with a
    053     * custom {@code EntityResolver}) or creating a custom entity resolver
    054     * and registering it with the XMLConfiguration is recommended.
    055     * </p>
    056     *
    057     * @param publicId Public identifier of the Entity to be resolved
    058     * @param entityURL The URL to use for reading this Entity
    059     * @throws IllegalArgumentException if the public ID is undefined
    060     */
    061    @Override
    062    public void registerEntityId(final String publicId, final URL entityURL)
    063    {
    064        if (publicId == null)
    065        {
    066            throw new IllegalArgumentException("Public ID must not be null!");
    067        }
    068        getRegisteredEntities().put(publicId, entityURL);
    069    }
    070
    071    /**
    072     * Resolves the requested external entity. This is the default
    073     * implementation of the {@code EntityResolver} interface. It checks
    074     * the passed in public ID against the registered entity IDs and uses a
    075     * local URL if possible.
    076     *
    077     * @param publicId the public identifier of the entity being referenced
    078     * @param systemId the system identifier of the entity being referenced
    079     * @return an input source for the specified entity
    080     * @throws org.xml.sax.SAXException if a parsing exception occurs
    081     */
    082    @Override
    083    public InputSource resolveEntity(final String publicId, final String systemId)
    084            throws SAXException
    085    {
    086        // Has this system identifier been registered?
    087        URL entityURL = null;
    088        if (publicId != null)
    089        {
    090            entityURL = getRegisteredEntities().get(publicId);
    091        }
    092
    093        if (entityURL != null)
    094        {
    095            // Obtain an InputSource for this URL. This code is based on the
    096            // createInputSourceFromURL() method of Commons Digester.
    097            try
    098            {
    099                final URLConnection connection = entityURL.openConnection();
    100                connection.setUseCaches(false);
    101                final InputStream stream = connection.getInputStream();
    102                final InputSource source = new InputSource(stream);
    103                source.setSystemId(entityURL.toExternalForm());
    104                return source;
    105            }
    106            catch (final IOException e)
    107            {
    108                throw new SAXException(e);
    109            }
    110        }
    111        // default processing behavior
    112        return null;
    113    }
    114
    115    /**
    116     * Returns a map with the entity IDs that have been registered using the
    117     * {@code registerEntityId()} method.
    118     *
    119     * @return a map with the registered entity IDs
    120     */
    121    @Override
    122    public Map<String, URL> getRegisteredEntities()
    123    {
    124        return registeredEntities;
    125    }
    126}