pylucene 3.5.0-3

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

diff --git a/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ngram/NGramTokenizer.java b/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ngram/NGramTokenizer.java
new file mode 100644 (file)
index 0000000..e7137c9
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+++ b/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ngram/NGramTokenizer.java
@@ -0,0 +1,147 @@
+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 org.apache.lucene.analysis.Tokenizer;
+import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
+import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
+import org.apache.lucene.util.AttributeSource;
+
+import java.io.IOException;
+import java.io.Reader;
+
+/**
+ * Tokenizes the input into n-grams of the given size(s).
+ */
+public final class NGramTokenizer extends Tokenizer {
+  public static final int DEFAULT_MIN_NGRAM_SIZE = 1;
+  public static final int DEFAULT_MAX_NGRAM_SIZE = 2;
+
+  private int minGram, maxGram;
+  private int gramSize;
+  private int pos = 0;
+  private int inLen;
+  private String inStr;
+  private boolean started = false;
+  
+  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
+  private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
+
+  /**
+   * Creates NGramTokenizer with given min and max n-grams.
+   * @param input {@link Reader} holding the input to be tokenized
+   * @param minGram the smallest n-gram to generate
+   * @param maxGram the largest n-gram to generate
+   */
+  public NGramTokenizer(Reader input, int minGram, int maxGram) {
+    super(input);
+    init(minGram, maxGram);
+  }
+
+  /**
+   * Creates NGramTokenizer with given min and max n-grams.
+   * @param source {@link AttributeSource} to use
+   * @param input {@link Reader} holding the input to be tokenized
+   * @param minGram the smallest n-gram to generate
+   * @param maxGram the largest n-gram to generate
+   */
+  public NGramTokenizer(AttributeSource source, Reader input, int minGram, int maxGram) {
+    super(source, input);
+    init(minGram, maxGram);
+  }
+
+  /**
+   * Creates NGramTokenizer with given min and max n-grams.
+   * @param factory {@link org.apache.lucene.util.AttributeSource.AttributeFactory} to use
+   * @param input {@link Reader} holding the input to be tokenized
+   * @param minGram the smallest n-gram to generate
+   * @param maxGram the largest n-gram to generate
+   */
+  public NGramTokenizer(AttributeFactory factory, Reader input, int minGram, int maxGram) {
+    super(factory, input);
+    init(minGram, maxGram);
+  }
+
+  /**
+   * Creates NGramTokenizer with default min and max n-grams.
+   * @param input {@link Reader} holding the input to be tokenized
+   */
+  public NGramTokenizer(Reader input) {
+    this(input, DEFAULT_MIN_NGRAM_SIZE, DEFAULT_MAX_NGRAM_SIZE);
+  }
+  
+  private void init(int minGram, int maxGram) {
+    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;
+  }
+
+  /** Returns the next token in the stream, or null at EOS. */
+  @Override
+  public final boolean incrementToken() throws IOException {
+    clearAttributes();
+    if (!started) {
+      started = true;
+      gramSize = minGram;
+      char[] chars = new char[1024];
+      input.read(chars);
+      inStr = new String(chars).trim();  // remove any trailing empty strings 
+      inLen = inStr.length();
+    }
+
+    if (pos+gramSize > inLen) {            // if we hit the end of the string
+      pos = 0;                           // reset to beginning of string
+      gramSize++;                        // increase n-gram size
+      if (gramSize > maxGram)            // we are done
+        return false;
+      if (pos+gramSize > inLen)
+        return false;
+    }
+
+    int oldPos = pos;
+    pos++;
+    termAtt.setEmpty().append(inStr, oldPos, oldPos+gramSize);
+    offsetAtt.setOffset(correctOffset(oldPos), correctOffset(oldPos+gramSize));
+    return true;
+  }
+  
+  @Override
+  public final void end() {
+    // set final offset
+    final int finalOffset = inLen;
+    this.offsetAtt.setOffset(finalOffset, finalOffset);
+  }    
+  
+  @Override
+  public void reset(Reader input) throws IOException {
+    super.reset(input);
+    reset();
+  }
+
+  @Override
+  public void reset() throws IOException {
+    super.reset();
+    started = false;
+    pos = 0;
+  }
+}