FieldFilter


1   /**
2    * FieldFilter.java
3    *
4    * Copyright (c) 2000 Douglass R. Cutting.
5    *
6    * This program is free software; you can redistribute it and/or modify
7    * it under the terms of the GNU General Public License as published by
8    * the Free Software Foundation; either version 2 of the License, or
9    * (at your option) any later version.
10   *
11   * This program is distributed in the hope that it will be useful,
12   * but WITHOUT ANY WARRANTY; without even the implied warranty of
13   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14   * GNU General Public License for more details.
15   *
16   * You should have received a copy of the GNU General Public License
17   * along with this program; if not, write to the Free Software
18   * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19   */
20  
21  package org.nemesis.forum.search;
22  
23  import java.io.IOException  ;
24  import java.util.BitSet  ;
25  
26  import org.apache.lucene.index.IndexReader;
27  import org.apache.lucene.index.Term;
28  import org.apache.lucene.index.TermDocs;
29  import org.apache.lucene.search.Filter;
30  
31  /**
32   * A Filter that restricts search results to Documents that match a specified
33   * Field value.
34   *
35   * For example, suppose you create a search index to make your catalog of widgets
36   * searchable. When indexing, you add a field to each Document called "color"
37   * that has one of the following values: "blue", "green", "yellow", or "red".
38   * Now suppose that a user is executing a query but only wants to see green
39   * widgets in the results. The following code snippet yields that behavior:
40   * <pre>
41   *     //In this example, we assume the Searcher and Query are already defined.
42   *     //Define a FieldFilter to only show green colored widgets.
43   *     Field myFilter = new FieldFilter("color", "green");
44   *     Hits queryResults = mySearcher.execute(myQuery, myFilter);
45   * </pre>
46   *
47   * @author Matt Tucker (matt@Yasna.com)
48   */
49  public class FieldFilter extends Filter {
50  
51      private String   field;
52      private String   value;
53      private Term searchTerm;
54  
55      /**
56       * Creates a new field filter. The name of the field and the value to filter
57       * on are specified. In order for a Document to pass this filter, it must:
58       * <ol>
59       *      <li>The given field must exist in the document.
60       *      <li>The field value in the Document must exactly match the given
61       *          value.</ol>
62       *
63       * @param field the name of the field to filter on.
64       * @param value the value of the field that search results must match.
65       */
66      public FieldFilter(String   field, String   value) {
67          this.field = field;
68          this.value = value;
69          searchTerm = new Term(field, value);
70      }
71  
72      public BitSet   bits(IndexReader reader) throws IOException   {
73          //Create a new BitSet with a capacity equal to the size of the index.
74          BitSet   bits = new BitSet  (reader.maxDoc());
75          //Get an enumeration of all the documents that match the specified field
76          //value.
77          TermDocs matchingDocs = reader.termDocs(searchTerm);
78          try {
79              while(matchingDocs.next()) {
80                  bits.set(matchingDocs.doc());
81              }
82          }
83          finally {
84              if (matchingDocs != null) {
85                  matchingDocs.close();
86              }
87          }
88          return bits;
89      }
90  }
91
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