pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / analyzers / common / src / java / org / apache / lucene / analysis / ngram / NGramTokenFilter.java

diff --git a/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ngram/NGramTokenFilter.java b/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ngram/NGramTokenFilter.java
new file mode 100644 (file)
index 0000000..c73208b
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+++ b/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ngram/NGramTokenFilter.java
@@ -0,0 +1,106 @@
+package org.apache.lucene.analysis.ngram;
+
+/**
+ * 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.TokenFilter;
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
+import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
+
+/**
+ * Tokenizes the input into n-grams of the given size(s).
+ */
+public final class NGramTokenFilter extends TokenFilter {
+  public static final int DEFAULT_MIN_NGRAM_SIZE = 1;
+  public static final int DEFAULT_MAX_NGRAM_SIZE = 2;
+
+  private int minGram, maxGram;
+  
+  private char[] curTermBuffer;
+  private int curTermLength;
+  private int curGramSize;
+  private int curPos;
+  private int tokStart;
+  
+  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
+  private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
+
+  /**
+   * Creates NGramTokenFilter with given min and max n-grams.
+   * @param input {@link TokenStream} holding the input to be tokenized
+   * @param minGram the smallest n-gram to generate
+   * @param maxGram the largest n-gram to generate
+   */
+  public NGramTokenFilter(TokenStream input, int minGram, int maxGram) {
+    super(input);
+    if (minGram < 1) {
+      throw new IllegalArgumentException("minGram must be greater than zero");
+    }
+    if (minGram > maxGram) {
+      throw new IllegalArgumentException("minGram must not be greater than maxGram");
+    }
+    this.minGram = minGram;
+    this.maxGram = maxGram;
+  }
+
+  /**
+   * Creates NGramTokenFilter with default min and max n-grams.
+   * @param input {@link TokenStream} holding the input to be tokenized
+   */
+  public NGramTokenFilter(TokenStream input) {
+    this(input, DEFAULT_MIN_NGRAM_SIZE, DEFAULT_MAX_NGRAM_SIZE);
+  }
+
+  /** Returns the next token in the stream, or null at EOS. */
+  @Override
+  public final boolean incrementToken() throws IOException {
+    while (true) {
+      if (curTermBuffer == null) {
+        if (!input.incrementToken()) {
+          return false;
+        } else {
+          curTermBuffer = termAtt.buffer().clone();
+          curTermLength = termAtt.length();
+          curGramSize = minGram;
+          curPos = 0;
+          tokStart = offsetAtt.startOffset();
+        }
+      }
+      while (curGramSize <= maxGram) {
+        while (curPos+curGramSize <= curTermLength) {     // while there is input
+          clearAttributes();
+          termAtt.copyBuffer(curTermBuffer, curPos, curGramSize);
+          offsetAtt.setOffset(tokStart + curPos, tokStart + curPos + curGramSize);
+          curPos++;
+          return true;
+        }
+        curGramSize++;                         // increase n-gram size
+        curPos = 0;
+      }
+      curTermBuffer = null;
+    }
+  }
+
+  @Override
+  public void reset() throws IOException {
+    super.reset();
+    curTermBuffer = null;
+  }
+}