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 java.io.IOException;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.miscellaneous.CodepointCountFilter;
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.CharacterUtils;
import org.apache.lucene.util.Version;
/**
* Tokenizes the input into n-grams of the given size(s).
* <a name="version"/>
* <p>You must specify the required {@link Version} compatibility when
* creating a {@link NGramTokenFilter}. As of Lucene 4.4, this token filters:<ul>
* <li>handles supplementary characters correctly,</li>
* <li>emits all n-grams for the same token at the same position,</li>
* <li>does not modify offsets,</li>
* <li>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").</li></ul>
* <p>You can make this filter use the old behavior by providing a version <
* {@link Version#LUCENE_4_4} in the constructor but this is not recommended as
* it will lead to broken {@link TokenStream}s that will cause highlighting
* bugs.
* <p>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 NGramTokenFilter extends TokenFilter {
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 boolean hasIllegalOffsets; // only if the length changed before this filter
private final Version version;
private final CharacterUtils charUtils;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final PositionIncrementAttribute posIncAtt;
private final PositionLengthAttribute posLenAtt;
private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
/**
* Creates NGramTokenFilter with given min and max n-grams.
* @param version Lucene version to enable correct position increments.
* See <a href="#version">above</a> 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 NGramTokenFilter(Version version, TokenStream input, int minGram, int maxGram) {
super(new CodepointCountFilter(version, input, minGram, Integer.MAX_VALUE));
this.version = version;
this.charUtils = version.onOrAfter(Version.LUCENE_4_4)
? CharacterUtils.getInstance(version)
: CharacterUtils.getJava4Instance();
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;
if (version.onOrAfter(Version.LUCENE_4_4)) {
posIncAtt = addAttribute(PositionIncrementAttribute.class);
posLenAtt = addAttribute(PositionLengthAttribute.class);
} else {
posIncAtt = new PositionIncrementAttribute() {
@Override
public void setPositionIncrement(int positionIncrement) {}
@Override
public int getPositionIncrement() {
return 0;
}
};
posLenAtt = new PositionLengthAttribute() {
@Override
public void setPositionLength(int positionLength) {}
@Override
public int getPositionLength() {
return 0;
}
};
}
}
/**
* Creates NGramTokenFilter with default min and max n-grams.
* @param version Lucene version to enable correct position increments.
* See <a href="#version">above</a> for details.
* @param input {@link TokenStream} holding the input to be tokenized
*/
public NGramTokenFilter(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 length by start + end offsets doesn't match the term text then assume
// this is a synonym and don't adjust the offsets.
hasIllegalOffsets = (tokStart + curTermLength) != tokEnd;
}
}
if (version.onOrAfter(Version.LUCENE_4_4)) {
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;
}
} else {
while (curGramSize <= maxGram) {
while (curPos+curGramSize <= curTermLength) { // while there is input
clearAttributes();
termAtt.copyBuffer(curTermBuffer, curPos, curGramSize);
if (hasIllegalOffsets) {
offsetAtt.setOffset(tokStart, tokEnd);
} else {
offsetAtt.setOffset(tokStart + curPos, tokStart + curPos + curGramSize);
}
curPos++;
return true;
}
curGramSize++; // increase n-gram size
curPos = 0;
}
}
curTermBuffer = null;
}
}
@Override
public void reset() throws IOException {
super.reset();
curTermBuffer = null;
}
}