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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.tika.parser;
18  
19  import java.io.IOException;
20  import java.io.InputStream;
21  import java.util.Set;
22  
23  import org.apache.tika.exception.TikaException;
24  import org.apache.tika.metadata.Metadata;
25  import org.apache.tika.mime.MediaType;
26  import org.xml.sax.ContentHandler;
27  import org.xml.sax.SAXException;
28  
29  /**
30   * Base class for parser implementations that want to delegate parts of the
31   * task of parsing an input document to another parser. The delegate parser
32   * is looked up from the parsing context using the {@link Parser} class as
33   * the key.
34   *
35   * @since Apache Tika 0.4, major changes in Tika 0.5
36   */
37  public class DelegatingParser implements Parser {
38  
39      /**
40       * Returns the parser instance to which parsing tasks should be delegated.
41       * The default implementation looks up the delegate parser from the given
42       * parse context, and uses an {@link EmptyParser} instance as a fallback.
43       * Subclasses can override this method to implement alternative delegation
44       * strategies.
45       *
46       * @since Apache Tika 0.7
47       * @param context parse context
48       * @return delegate parser
49       */
50      protected Parser getDelegateParser(ParseContext context) {
51          return context.get(Parser.class, EmptyParser.INSTANCE);
52      }
53  
54      public Set<MediaType> getSupportedTypes(ParseContext context) {
55          return getDelegateParser(context).getSupportedTypes(context);
56      }
57  
58      /**
59       * Looks up the delegate parser from the parsing context and
60       * delegates the parse operation to it. If a delegate parser is not
61       * found, then an empty XHTML document is returned.
62       * <p>
63       * Subclasses should override this method to parse the top level
64       * structure of the given document stream. Parsed sub-streams can
65       * be passed to this base class method to be parsed by the configured
66       * delegate parser.
67       */
68      public void parse(
69              InputStream stream, ContentHandler handler,
70              Metadata metadata, ParseContext context)
71              throws SAXException, IOException, TikaException {
72          getDelegateParser(context).parse(stream, handler, metadata, context);
73      }
74  
75      /**
76       * @deprecated This method will be removed in Apache Tika 1.0.
77       */
78      public void parse(
79              InputStream stream, ContentHandler handler, Metadata metadata)
80              throws IOException, SAXException, TikaException {
81          parse(stream, handler, metadata, new ParseContext());
82      }
83  
84  }