+++ /dev/null
-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.apache.lucene.analysis.TokenFilter;
-import org.apache.lucene.analysis.TokenStream;
-import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
-import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
-
-import java.io.IOException;
-
-/**
- * Tokenizes the given token into n-grams of given size(s).
- * <p>
- * This {@link TokenFilter} create n-grams from the beginning edge or ending edge of a input token.
- * </p>
- */
-public final class EdgeNGramTokenFilter extends TokenFilter {
- public static final Side DEFAULT_SIDE = Side.FRONT;
- public static final int DEFAULT_MAX_GRAM_SIZE = 1;
- public static final int DEFAULT_MIN_GRAM_SIZE = 1;
-
- /** Specifies which side of the input the n-gram should be generated from */
- public static enum Side {
-
- /** Get the n-gram from the front of the input */
- FRONT {
- @Override
- public String getLabel() { return "front"; }
- },
-
- /** Get the n-gram from the end of the input */
- BACK {
- @Override
- public String getLabel() { return "back"; }
- };
-
- public abstract String getLabel();
-
- // Get the appropriate Side from a string
- public static Side getSide(String sideName) {
- if (FRONT.getLabel().equals(sideName)) {
- return FRONT;
- }
- if (BACK.getLabel().equals(sideName)) {
- return BACK;
- }
- return null;
- }
- }
-
- private final int minGram;
- private final int maxGram;
- private Side side;
- private char[] curTermBuffer;
- private int curTermLength;
- private int curGramSize;
- private int tokStart;
-
- private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
- private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.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 side the {@link Side} from which to chop off an n-gram
- * @param minGram the smallest n-gram to generate
- * @param maxGram the largest n-gram to generate
- */
- public EdgeNGramTokenFilter(TokenStream input, Side side, int minGram, int maxGram) {
- super(input);
-
- if (side == null) {
- throw new IllegalArgumentException("sideLabel must be either front or back");
- }
-
- 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;
- this.side = side;
- }
-
- /**
- * 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 sideLabel the name of the {@link Side} from which to chop off an n-gram
- * @param minGram the smallest n-gram to generate
- * @param maxGram the largest n-gram to generate
- */
- public EdgeNGramTokenFilter(TokenStream input, String sideLabel, int minGram, int maxGram) {
- this(input, Side.getSide(sideLabel), minGram, 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();
- curGramSize = minGram;
- tokStart = offsetAtt.startOffset();
- }
- }
- if (curGramSize <= maxGram) {
- if (! (curGramSize > curTermLength // if the remaining input is too short, we can't generate any n-grams
- || curGramSize > maxGram)) { // if we have hit the end of our n-gram size range, quit
- // grab gramSize chars from front or back
- int start = side == Side.FRONT ? 0 : curTermLength - curGramSize;
- int end = start + curGramSize;
- clearAttributes();
- offsetAtt.setOffset(tokStart + start, tokStart + end);
- termAtt.copyBuffer(curTermBuffer, start, curGramSize);
- curGramSize++;
- return true;
- }
- }
- curTermBuffer = null;
- }
- }
-
- @Override
- public void reset() throws IOException {
- super.reset();
- curTermBuffer = null;
- }
-}
fnp / pylucene.git / blobdiff