pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / analysis / PorterStemFilter.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/analysis/PorterStemFilter.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/analysis/PorterStemFilter.java
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+package org.apache.lucene.analysis;
+
+/**
+ * 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.
+ */
+
+import java.io.IOException;
+
+import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;
+import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
+
+/** Transforms the token stream as per the Porter stemming algorithm.
+    Note: the input to the stemming filter must already be in lower case,
+    so you will need to use LowerCaseFilter or LowerCaseTokenizer farther
+    down the Tokenizer chain in order for this to work properly!
+    <P>
+    To use this filter with other analyzers, you'll want to write an
+    Analyzer class that sets up the TokenStream chain as you want it.
+    To use this with LowerCaseTokenizer, for example, you'd write an
+    analyzer like this:
+    <P>
+    <PRE>
+    class MyAnalyzer extends Analyzer {
+      public final TokenStream tokenStream(String fieldName, Reader reader) {
+        return new PorterStemFilter(new LowerCaseTokenizer(reader));
+      }
+    }
+    </PRE>
+    <p>
+    Note: This filter is aware of the {@link KeywordAttribute}. To prevent
+    certain terms from being passed to the stemmer
+    {@link KeywordAttribute#isKeyword()} should be set to <code>true</code>
+    in a previous {@link TokenStream}.
+    </p>
+*/
+public final class PorterStemFilter extends TokenFilter {
+  private final PorterStemmer stemmer = new PorterStemmer();
+  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
+  private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);
+
+  public PorterStemFilter(TokenStream in) {
+    super(in);
+  }
+
+  @Override
+  public final boolean incrementToken() throws IOException {
+    if (!input.incrementToken())
+      return false;
+
+    if ((!keywordAttr.isKeyword()) && stemmer.stem(termAtt.buffer(), 0, termAtt.length()))
+      termAtt.copyBuffer(stemmer.getResultBuffer(), 0, stemmer.getResultLength());
+    return true;
+  }
+}