pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / analyzers / stempel / src / java / org / apache / lucene / analysis / stempel / StempelFilter.java

diff --git a/lucene-java-3.5.0/lucene/contrib/analyzers/stempel/src/java/org/apache/lucene/analysis/stempel/StempelFilter.java b/lucene-java-3.5.0/lucene/contrib/analyzers/stempel/src/java/org/apache/lucene/analysis/stempel/StempelFilter.java
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+/**
+ * Copyright 2004 The Apache Software Foundation
+ * 
+ * Licensed 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.
+ */
+
+package org.apache.lucene.analysis.stempel;
+
+import java.io.IOException;
+
+import org.apache.lucene.analysis.TokenFilter;
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
+import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;
+
+/**
+ * Transforms the token stream as per the stemming algorithm.
+ * <p>
+ * 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!
+ */
+public final class StempelFilter extends TokenFilter {
+  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
+  private final KeywordAttribute keywordAtt = addAttribute(KeywordAttribute.class);
+  private final StempelStemmer stemmer;
+  private final int minLength;
+  
+  /**
+   * Minimum length of input words to be processed. Shorter words are returned
+   * unchanged.
+   */
+  public static final int DEFAULT_MIN_LENGTH = 3;
+  
+  /**
+   * Create filter using the supplied stemming table.
+   * 
+   * @param in input token stream
+   * @param stemmer stemmer
+   */
+  public StempelFilter(TokenStream in, StempelStemmer stemmer) {
+    this(in, stemmer, DEFAULT_MIN_LENGTH);
+  }
+  
+  /**
+   * Create filter using the supplied stemming table.
+   * 
+   * @param in input token stream
+   * @param stemmer stemmer
+   * @param minLength For performance reasons words shorter than minLength
+   * characters are not processed, but simply returned.
+   */
+  public StempelFilter(TokenStream in, StempelStemmer stemmer, int minLength) {
+    super(in);
+    this.stemmer = stemmer;
+    this.minLength = minLength;
+  }
+  
+  /** Returns the next input Token, after being stemmed */
+  @Override
+  public boolean incrementToken() throws IOException {
+    if (input.incrementToken()) {
+      if (!keywordAtt.isKeyword() && termAtt.length() > minLength) {
+        StringBuilder sb = stemmer.stem(termAtt);
+        if (sb != null) // if we can't stem it, return unchanged
+          termAtt.setEmpty().append(sb);
+      }
+      return true;
+    } else {
+      return false;
+    }
+  }
+}