Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.configuration.resolver; import java.io.IOException; import java.io.InputStream; import java.net.URL; import java.net.URLConnection; import java.util.HashMap; import java.util.Map; import org.xml.sax.EntityResolver; import org.xml.sax.InputSource; import org.xml.sax.SAXException; /** * The DefaultEntityResolver used by XML Configurations. * @author <a * href="http://commons.apache.org/configuration/team-list.html">Commons * Configuration team</a> * @since 1.7 * @version $Id: DefaultEntityResolver.java 1571738 2014-02-25 16:42:18Z ggregory $ */ public class DefaultEntityResolver implements EntityResolver, EntityRegistry { /** Stores a map with the registered public IDs.*/ private final Map<String, URL> registeredEntities = new HashMap<String, URL>(); /** * <p> * Registers the specified URL for the specified public identifier. * </p> * <p> * This implementation maps {@code PUBLICID}'s to URLs (from which * the resource will be loaded). A common use case for this method is to * register local URLs (possibly computed at runtime by a class loader) for * DTDs and Schemas. This allows the performance advantage of using a local * version without having to ensure every {@code SYSTEM} URI on every * processed XML document is local. This implementation provides only basic * functionality. If more sophisticated features are required, either calling * {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom * {@code DocumentBuilder} (which also can be initialized with a * custom {@code EntityResolver}) or creating a custom entity resolver * and registering it with the XMLConfiguration is recommended. * </p> * * @param publicId Public identifier of the Entity to be resolved * @param entityURL The URL to use for reading this Entity * @throws IllegalArgumentException if the public ID is undefined */ @Override public void registerEntityId(String publicId, URL entityURL) { if (publicId == null) { throw new IllegalArgumentException("Public ID must not be null!"); } getRegisteredEntities().put(publicId, entityURL); } /** * Resolves the requested external entity. This is the default * implementation of the {@code EntityResolver} interface. It checks * the passed in public ID against the registered entity IDs and uses a * local URL if possible. * * @param publicId the public identifier of the entity being referenced * @param systemId the system identifier of the entity being referenced * @return an input source for the specified entity * @throws org.xml.sax.SAXException if a parsing exception occurs */ @Override public InputSource resolveEntity(String publicId, String systemId) throws SAXException { // Has this system identifier been registered? URL entityURL = null; if (publicId != null) { entityURL = getRegisteredEntities().get(publicId); } if (entityURL != null) { // Obtain an InputSource for this URL. This code is based on the // createInputSourceFromURL() method of Commons Digester. try { URLConnection connection = entityURL.openConnection(); connection.setUseCaches(false); InputStream stream = connection.getInputStream(); InputSource source = new InputSource(stream); source.setSystemId(entityURL.toExternalForm()); return source; } catch (IOException e) { throw new SAXException(e); } } else { // default processing behavior return null; } } /** * Returns a map with the entity IDs that have been registered using the * {@code registerEntityId()} method. * * @return a map with the registered entity IDs */ @Override public Map<String, URL> getRegisteredEntities() { return registeredEntities; } }