lucene/analysis/common/src/java/org/apache/lucene/analysis/th/ThaiTokenizer.java

/*
 * 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.
 */
package org.apache.lucene.analysis.th;


import java.text.BreakIterator;
import java.util.Locale;

import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.util.CharArrayIterator;
import org.apache.lucene.analysis.util.SegmentingTokenizerBase;
import org.apache.lucene.util.AttributeFactory;

/**
 * Tokenizer that use {@link BreakIterator} to tokenize Thai text.
 * <p>WARNING: this tokenizer may not be supported by all JREs.
 *    It is known to work with Sun/Oracle and Harmony JREs.
 *    If your application needs to be fully portable, consider using ICUTokenizer instead,
 *    which uses an ICU Thai BreakIterator that will always be available.
 */
public class ThaiTokenizer extends SegmentingTokenizerBase {
  /** 
   * True if the JRE supports a working dictionary-based breakiterator for Thai.
   * If this is false, this tokenizer will not work at all!
   */
  public static final boolean DBBI_AVAILABLE;
  private static final BreakIterator proto = BreakIterator.getWordInstance(new Locale("th"));
  static {
    // check that we have a working dictionary-based break iterator for thai
    proto.setText("ภาษาไทย");
    DBBI_AVAILABLE = proto.isBoundary(4);
  }
  
  /** used for breaking the text into sentences */
  private static final BreakIterator sentenceProto = BreakIterator.getSentenceInstance(Locale.ROOT);
  
  private final BreakIterator wordBreaker;
  private final CharArrayIterator wrapper = CharArrayIterator.newWordInstance();
  
  int sentenceStart;
  int sentenceEnd;
  
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
  
  /** Creates a new ThaiTokenizer */
  public ThaiTokenizer() {
    this(DEFAULT_TOKEN_ATTRIBUTE_FACTORY);
  }
      
  /** Creates a new ThaiTokenizer, supplying the AttributeFactory */
  public ThaiTokenizer(AttributeFactory factory) {
    super(factory, (BreakIterator)sentenceProto.clone());
    if (!DBBI_AVAILABLE) {
      throw new UnsupportedOperationException("This JRE does not have support for Thai segmentation");
    }
    wordBreaker = (BreakIterator)proto.clone();
  }

  @Override
  protected void setNextSentence(int sentenceStart, int sentenceEnd) {
    this.sentenceStart = sentenceStart;
    this.sentenceEnd = sentenceEnd;
    wrapper.setText(buffer, sentenceStart, sentenceEnd - sentenceStart);
    wordBreaker.setText(wrapper);
  }

  @Override
  protected boolean incrementWord() {
    int start = wordBreaker.current();
    if (start == BreakIterator.DONE) {
      return false; // BreakIterator exhausted
    }

    // find the next set of boundaries, skipping over non-tokens
    int end = wordBreaker.next();
    while (end != BreakIterator.DONE &&
           !Character.isLetterOrDigit(Character.codePointAt(buffer, sentenceStart + start, sentenceEnd))) {
      start = end;
      end = wordBreaker.next();
    }

    if (end == BreakIterator.DONE) {
      return false; // BreakIterator exhausted
    }

    clearAttributes();
    termAtt.copyBuffer(buffer, sentenceStart + start, end - start);
    offsetAtt.setOffset(correctOffset(offset + sentenceStart + start), correctOffset(offset + sentenceStart + end));
    return true;
  }
}