Lucene example source code file (ICUTokenizer.java)

This example Lucene source code file (ICUTokenizer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

breakiterator, compositebreakiterator, defaulticutokenizerconfig, icutokenizer, icutokenizer, icutokenizerconfig, io, iobuffer, iobuffer, ioexception, ioexception, override, override, tokenizer, typeattribute

The Lucene ICUTokenizer.java source code

package org.apache.lucene.analysis.icu.segmentation;

/**
 * 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 java.io.Reader;

import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.icu.tokenattributes.ScriptAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;

import com.ibm.icu.lang.UCharacter;
import com.ibm.icu.text.BreakIterator;

/**
 * Breaks text into words according to UAX #29: Unicode Text Segmentation
 * (http://www.unicode.org/reports/tr29/)
 * <p>
 * Words are broken across script boundaries, then segmented according to
 * the BreakIterator and typing provided by the {@link ICUTokenizerConfig}
 * </p>
 * @see ICUTokenizerConfig
 * @lucene.experimental
 */
public final class ICUTokenizer extends Tokenizer {
  private static final int IOBUFFER = 4096;
  private final char buffer[] = new char[IOBUFFER];
  /** true length of text in the buffer */
  private int length = 0; 
  /** length in buffer that can be evaluated safely, up to a safe end point */
  private int usableLength = 0; 
  /** accumulated offset of previous buffers for this reader, for offsetAtt */
  private int offset = 0; 

  private final CompositeBreakIterator breaker; /* tokenizes a char[] of text */
  private final ICUTokenizerConfig config;
  private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final TypeAttribute typeAtt = addAttribute(TypeAttribute.class);
  private final ScriptAttribute scriptAtt = addAttribute(ScriptAttribute.class);

  /**
   * Construct a new ICUTokenizer that breaks text into words from the given
   * Reader.
   * <p>
   * The default script-specific handling is used.
   * 
   * @param input Reader containing text to tokenize.
   * @see DefaultICUTokenizerConfig
   */
  public ICUTokenizer(Reader input) {
    this(input, new DefaultICUTokenizerConfig());
  }

  /**
   * Construct a new ICUTokenizer that breaks text into words from the given
   * Reader, using a tailored BreakIterator configuration.
   *
   * @param input Reader containing text to tokenize.
   * @param config Tailored BreakIterator configuration 
   */
  public ICUTokenizer(Reader input, ICUTokenizerConfig config) {
    super(input);
    this.config = config;
    breaker = new CompositeBreakIterator(config);
  }

  @Override
  public boolean incrementToken() throws IOException {
    clearAttributes();
    if (length == 0)
      refill();
    while (!incrementTokenBuffer()) {
      refill();
      if (length <= 0) // no more bytes to read;
        return false;
    }
    return true;
  }
  
  @Override
  public void reset() throws IOException {
    super.reset();
    breaker.setText(buffer, 0, 0);
    length = usableLength = offset = 0;
  }

  @Override
  public void reset(Reader input) throws IOException {
    super.reset(input);
    reset();
  }
  
  @Override
  public void end() throws IOException {
    final int finalOffset = (length < 0) ? offset : offset + length;
    offsetAtt.setOffset(finalOffset, finalOffset);
  }  

  /*
   * This tokenizes text based upon the longest matching rule, and because of 
   * this, isn't friendly to a Reader.
   * 
   * Text is read from the input stream in 4kB chunks. Within a 4kB chunk of
   * text, the last unambiguous break point is found (in this implementation:
   * white space character) Any remaining characters represent possible partial
   * words, so are appended to the front of the next chunk.
   * 
   * There is the possibility that there are no unambiguous break points within
   * an entire 4kB chunk of text (binary data). So there is a maximum word limit
   * of 4kB since it will not try to grow the buffer in this case.
   */

  /**
   * Returns the last unambiguous break position in the text.
   * 
   * @return position of character, or -1 if one does not exist
   */
  private int findSafeEnd() {
    for (int i = length - 1; i >= 0; i--)
      if (UCharacter.isWhitespace(buffer[i]))
        return i + 1;
    return -1;
  }

  /**
   * Refill the buffer, accumulating the offset and setting usableLength to the
   * last unambiguous break position
   * 
   * @throws IOException
   */
  private void refill() throws IOException {
    offset += usableLength;
    int leftover = length - usableLength;
    System.arraycopy(buffer, usableLength, buffer, 0, leftover);
    int requested = buffer.length - leftover;
    int returned = input.read(buffer, leftover, requested);
    length = returned < 0 ? leftover : returned + leftover;
    if (returned < requested) /* reader has been emptied, process the rest */
      usableLength = length;
    else { /* still more data to be read, find a safe-stopping place */
      usableLength = findSafeEnd();
      if (usableLength < 0)
        usableLength = length; /*
                                * more than IOBUFFER of text without space,
                                * gonna possibly truncate tokens
                                */
    }

    breaker.setText(buffer, 0, Math.max(0, usableLength));
  }

  /*
   * return true if there is a token from the buffer, or null if it is
   * exhausted.
   */
  private boolean incrementTokenBuffer() {
    int start = breaker.current();
    if (start == BreakIterator.DONE)
      return false; // BreakIterator exhausted

    // find the next set of boundaries, skipping over non-tokens (rule status 0)
    int end = breaker.next();
    while (start != BreakIterator.DONE && breaker.getRuleStatus() == 0) {
      start = end;
      end = breaker.next();
    }

    if (start == BreakIterator.DONE)
      return false; // BreakIterator exhausted

    termAtt.copyBuffer(buffer, start, end - start);
    offsetAtt.setOffset(correctOffset(offset + start), correctOffset(offset + end));
    typeAtt.setType(config.getType(breaker.getScriptCode(), breaker.getRuleStatus()));
    scriptAtt.setCode(breaker.getScriptCode());

    return true;
  }
}