org.apache.lucene.analysis.cn.smart.HMMChineseTokenizer.java Source code

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Here is the source code for org.apache.lucene.analysis.cn.smart.HMMChineseTokenizer.java

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/*
 * 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.cn.smart;

import java.io.IOException;
import java.text.BreakIterator;
import java.util.Iterator;
import java.util.Locale;

import org.apache.lucene.analysis.cn.smart.hhmm.SegToken;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;
import org.apache.lucene.analysis.util.SegmentingTokenizerBase;
import org.apache.lucene.util.AttributeFactory;

/**
 * Tokenizer for Chinese or mixed Chinese-English text.
 * <p>
 * The analyzer uses probabilistic knowledge to find the optimal word segmentation for Simplified Chinese text.
 * The text is first broken into sentences, then each sentence is segmented into words.
 */
public class HMMChineseTokenizer extends SegmentingTokenizerBase {
    /** used for breaking the text into sentences */
    private static final BreakIterator sentenceProto = BreakIterator.getSentenceInstance(Locale.ROOT);

    private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
    private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
    private final TypeAttribute typeAtt = addAttribute(TypeAttribute.class);

    private final WordSegmenter wordSegmenter = new WordSegmenter();
    private Iterator<SegToken> tokens;

    /** Creates a new HMMChineseTokenizer */
    public HMMChineseTokenizer() {
        this(DEFAULT_TOKEN_ATTRIBUTE_FACTORY);
    }

    /** Creates a new HMMChineseTokenizer, supplying the AttributeFactory */
    public HMMChineseTokenizer(AttributeFactory factory) {
        super(factory, (BreakIterator) sentenceProto.clone());
    }

    @Override
    protected void setNextSentence(int sentenceStart, int sentenceEnd) {
        String sentence = new String(buffer, sentenceStart, sentenceEnd - sentenceStart);
        tokens = wordSegmenter.segmentSentence(sentence, offset + sentenceStart).iterator();
    }

    @Override
    protected boolean incrementWord() {
        if (tokens == null || !tokens.hasNext()) {
            return false;
        } else {
            SegToken token = tokens.next();
            clearAttributes();
            termAtt.copyBuffer(token.charArray, 0, token.charArray.length);
            offsetAtt.setOffset(correctOffset(token.startOffset), correctOffset(token.endOffset));
            typeAtt.setType("word");
            return true;
        }
    }

    @Override
    public void reset() throws IOException {
        super.reset();
        tokens = null;
    }
}