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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.configuration.resolver;
18  
19  import java.io.IOException;
20  import java.io.InputStream;
21  import java.net.URL;
22  import java.net.URLConnection;
23  import java.util.HashMap;
24  import java.util.Map;
25  
26  import org.xml.sax.EntityResolver;
27  import org.xml.sax.InputSource;
28  import org.xml.sax.SAXException;
29  
30  /**
31   * The DefaultEntityResolver used by XML Configurations.
32   * @author <a
33   * href="http://commons.apache.org/configuration/team-list.html">Commons
34   * Configuration team</a>
35   * @since 1.7
36   * @version $Id: DefaultEntityResolver.java 1301991 2012-03-17 20:18:02Z sebb $
37   */
38  public class DefaultEntityResolver implements EntityResolver, EntityRegistry
39  {
40      /** Stores a map with the registered public IDs.*/
41      private Map<String, URL> registeredEntities = new HashMap<String, URL>();
42  
43      /**
44       * <p>
45       * Registers the specified URL for the specified public identifier.
46       * </p>
47       * <p>
48       * This implementation maps {@code PUBLICID}'s to URLs (from which
49       * the resource will be loaded). A common use case for this method is to
50       * register local URLs (possibly computed at runtime by a class loader) for
51       * DTDs and Schemas. This allows the performance advantage of using a local
52       * version without having to ensure every {@code SYSTEM} URI on every
53       * processed XML document is local. This implementation provides only basic
54       * functionality. If more sophisticated features are required, either calling
55       * {@code XMLConfiguration.setDocumentBuilder(DocumentBuilder)} to set a custom
56       * {@code DocumentBuilder} (which also can be initialized with a
57       * custom {@code EntityResolver}) or creating a custom entity resolver
58       * and registering it with the XMLConfiguration is recommended.
59       * </p>
60       *
61       * @param publicId Public identifier of the Entity to be resolved
62       * @param entityURL The URL to use for reading this Entity
63       * @throws IllegalArgumentException if the public ID is undefined
64       */
65      public void registerEntityId(String publicId, URL entityURL)
66      {
67          if (publicId == null)
68          {
69              throw new IllegalArgumentException("Public ID must not be null!");
70          }
71          getRegisteredEntities().put(publicId, entityURL);
72      }
73  
74      /**
75       * Resolves the requested external entity. This is the default
76       * implementation of the {@code EntityResolver} interface. It checks
77       * the passed in public ID against the registered entity IDs and uses a
78       * local URL if possible.
79       *
80       * @param publicId the public identifier of the entity being referenced
81       * @param systemId the system identifier of the entity being referenced
82       * @return an input source for the specified entity
83       * @throws org.xml.sax.SAXException if a parsing exception occurs
84       */
85      public InputSource resolveEntity(String publicId, String systemId)
86              throws SAXException
87      {
88          // Has this system identifier been registered?
89          URL entityURL = null;
90          if (publicId != null)
91          {
92              entityURL = getRegisteredEntities().get(publicId);
93          }
94  
95          if (entityURL != null)
96          {
97              // Obtain an InputSource for this URL. This code is based on the
98              // createInputSourceFromURL() method of Commons Digester.
99              try
100             {
101                 URLConnection connection = entityURL.openConnection();
102                 connection.setUseCaches(false);
103                 InputStream stream = connection.getInputStream();
104                 InputSource source = new InputSource(stream);
105                 source.setSystemId(entityURL.toExternalForm());
106                 return source;
107             }
108             catch (IOException e)
109             {
110                 throw new SAXException(e);
111             }
112         }
113         else
114         {
115             // default processing behavior
116             return null;
117         }
118     }
119 
120     /**
121      * Returns a map with the entity IDs that have been registered using the
122      * {@code registerEntityId()} method.
123      *
124      * @return a map with the registered entity IDs
125      */
126     public Map<String, URL> getRegisteredEntities()
127     {
128         return registeredEntities;
129     }
130 }