KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > org > apache > lucene > analysis > PorterStemFilter


1 package org.apache.lucene.analysis;
2
3 /**
4  * Copyright 2004 The Apache Software Foundation
5  *
6  * Licensed under the Apache License, Version 2.0 (the "License");
7  * you may not use this file except in compliance with the License.
8  * You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18
19 import java.io.IOException JavaDoc;
20
21 /** Transforms the token stream as per the Porter stemming algorithm.
22     Note: the input to the stemming filter must already be in lower case,
23     so you will need to use LowerCaseFilter or LowerCaseTokenizer farther
24     down the Tokenizer chain in order for this to work properly!
25     <P>
26     To use this filter with other analyzers, you'll want to write an
27     Analyzer class that sets up the TokenStream chain as you want it.
28     To use this with LowerCaseTokenizer, for example, you'd write an
29     analyzer like this:
30     <P>
31     <PRE>
32     class MyAnalyzer extends Analyzer {
33       public final TokenStream tokenStream(String fieldName, Reader reader) {
34         return new PorterStemFilter(new LowerCaseTokenizer(reader));
35       }
36     }
37     </PRE>
38 */
39 public final class PorterStemFilter extends TokenFilter {
40   private PorterStemmer stemmer;
41
42   public PorterStemFilter(TokenStream in) {
43     super(in);
44     stemmer = new PorterStemmer();
45   }
46
47   /** Returns the next input Token, after being stemmed */
48   public final Token next() throws IOException JavaDoc {
49     Token token = input.next();
50     if (token == null)
51       return null;
52     else {
53       String JavaDoc s = stemmer.stem(token.termText);
54       if (s != token.termText) // Yes, I mean object reference comparison here
55 token.termText = s;
56       return token;
57     }
58   }
59 }
60
Popular Tags