org.apache.lucene.analysis.ngram.XNGramTokenFilter Maven / Gradle / Ivy
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.elasticsearch.common.lucene.Lucene;
import java.io.IOException;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.miscellaneous.LengthFilter;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionLengthAttribute;
import org.apache.lucene.analysis.util.XCharacterUtils;
import org.apache.lucene.util.Version;
/**
* Tokenizes the input into n-grams of the given size(s).
*
* You must specify the required {@link Version} compatibility when
* creating a {@link XNGramTokenFilter}. As of Lucene 4.4, this token filters:
* - handles supplementary characters correctly,
* - emits all n-grams for the same token at the same position,
* - does not modify offsets,
* - sorts n-grams by their offset in the original token first, then
* increasing length (meaning that "abc" will give "a", "ab", "abc", "b", "bc",
* "c").
* You can make this filter use the old behavior by providing a version <
* {@link Version#LUCENE_44} in the constructor but this is not recommended as
* it will lead to broken {@link TokenStream}s that will cause highlighting
* bugs.
*
If you were using this {@link TokenFilter} to perform partial highlighting,
* this won't work anymore since this filter doesn't update offsets. You should
* modify your analysis chain to use {@link NGramTokenizer}, and potentially
* override {@link NGramTokenizer#isTokenChar(int)} to perform pre-tokenization.
*/
public final class XNGramTokenFilter extends TokenFilter {
static {
// LUCENE MONITOR: this should be in Lucene 4.4 copied from Revision: 1492640.
assert Lucene.VERSION == Version.LUCENE_43 : "Elasticsearch has upgraded to Lucene Version: [" + Lucene.VERSION + "] this class should be removed";
}
public static final int DEFAULT_MIN_NGRAM_SIZE = 1;
public static final int DEFAULT_MAX_NGRAM_SIZE = 2;
private final int minGram, maxGram;
private char[] curTermBuffer;
private int curTermLength;
private int curCodePointCount;
private int curGramSize;
private int curPos;
private int curPosInc, curPosLen;
private int tokStart;
private int tokEnd;
private final XCharacterUtils charUtils;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final PositionIncrementAttribute posIncAtt;
private final PositionLengthAttribute posLenAtt;
private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
/**
* Creates XNGramTokenFilter with given min and max n-grams.
* @param version Lucene version to enable correct position increments.
* See above for details.
* @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 XNGramTokenFilter(Version version, TokenStream input, int minGram, int maxGram) {
super(new LengthFilter(true, input, minGram, Integer.MAX_VALUE));
this.charUtils = XCharacterUtils.getInstance(version);
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;
posIncAtt = addAttribute(PositionIncrementAttribute.class);
posLenAtt = addAttribute(PositionLengthAttribute.class);
}
/**
* Creates XNGramTokenFilter with default min and max n-grams.
* @param version Lucene version to enable correct position increments.
* See above for details.
* @param input {@link TokenStream} holding the input to be tokenized
*/
public XNGramTokenFilter(Version version, TokenStream input) {
this(version, 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();
curCodePointCount = charUtils.codePointCount(termAtt);
curGramSize = minGram;
curPos = 0;
curPosInc = posIncAtt.getPositionIncrement();
curPosLen = posLenAtt.getPositionLength();
tokStart = offsetAtt.startOffset();
tokEnd = offsetAtt.endOffset();
}
}
if (curGramSize > maxGram || (curPos + curGramSize) > curCodePointCount) {
++curPos;
curGramSize = minGram;
}
if ((curPos + curGramSize) <= curCodePointCount) {
clearAttributes();
final int start = charUtils.offsetByCodePoints(curTermBuffer, 0, curTermLength, 0, curPos);
final int end = charUtils.offsetByCodePoints(curTermBuffer, 0, curTermLength, start, curGramSize);
termAtt.copyBuffer(curTermBuffer, start, end - start);
posIncAtt.setPositionIncrement(curPosInc);
curPosInc = 0;
posLenAtt.setPositionLength(curPosLen);
offsetAtt.setOffset(tokStart, tokEnd);
curGramSize++;
return true;
}
curTermBuffer = null;
}
}
@Override
public void reset() throws IOException {
super.reset();
curTermBuffer = null;
}
}