/*
* 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.ngram;
import java.io.IOException;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
/**
* Tokenizes the given token into n-grams of given size(s).
* <p>
* This {@link TokenFilter} create n-grams from the beginning edge of a input token.
* <p><a name="match_version"></a>As of Lucene 4.4, this filter handles correctly
* supplementary characters.
*/
public final class EdgeNGramTokenFilter extends TokenFilter {
public static final int DEFAULT_MAX_GRAM_SIZE = 1;
public static final int DEFAULT_MIN_GRAM_SIZE = 1;
private final int minGram;
private final int maxGram;
private char[] curTermBuffer;
private int curTermLength;
private int curCodePointCount;
private int curGramSize;
private int savePosIncr;
private State state;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final PositionIncrementAttribute posIncrAtt = addAttribute(PositionIncrementAttribute.class);
/**
* Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range
*
* @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 EdgeNGramTokenFilter(TokenStream input, int minGram, int maxGram) {
super(input);
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;
}
@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 = Character.codePointCount(termAtt, 0, termAtt.length());
curGramSize = minGram;
state = captureState();
savePosIncr += posIncrAtt.getPositionIncrement();
}
}
if (curGramSize <= maxGram) { // if we have hit the end of our n-gram size range, quit
if (curGramSize <= curCodePointCount) { // if the remaining input is too short, we can't generate any n-grams
// grab gramSize chars from front or back
restoreState(state);
// first ngram gets increment, others don't
if (curGramSize == minGram) {
posIncrAtt.setPositionIncrement(savePosIncr);
savePosIncr = 0;
} else {
posIncrAtt.setPositionIncrement(0);
}
final int charLength = Character.offsetByCodePoints(curTermBuffer, 0, curTermLength, 0, curGramSize);
termAtt.copyBuffer(curTermBuffer, 0, charLength);
curGramSize++;
return true;
}
}
curTermBuffer = null;
}
}
@Override
public void reset() throws IOException {
super.reset();
curTermBuffer = null;
savePosIncr = 0;
}
}