| /* |
| * 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.ja; |
| |
| |
| 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.KeywordAttribute; |
| |
| import java.io.IOException; |
| |
| /** |
| * A {@link TokenFilter} that normalizes common katakana spelling variations |
| * ending in a long sound character by removing this character (U+30FC). Only |
| * katakana words longer than a minimum length are stemmed (default is four). |
| * <p> |
| * Note that only full-width katakana characters are supported. Please use a |
| * {@link org.apache.lucene.analysis.cjk.CJKWidthFilter} to convert half-width |
| * katakana to full-width before using this filter. |
| * </p> |
| * <p> |
| * In order to prevent terms from being stemmed, use an instance of |
| * {@link org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter} |
| * or a custom {@link TokenFilter} that sets the {@link KeywordAttribute} |
| * before this {@link TokenStream}. |
| * </p> |
| */ |
| |
| public final class JapaneseKatakanaStemFilter extends TokenFilter { |
| public final static int DEFAULT_MINIMUM_LENGTH = 4; |
| private final static char HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK = '\u30fc'; |
| |
| private final CharTermAttribute termAttr = addAttribute(CharTermAttribute.class); |
| private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class); |
| private final int minimumKatakanaLength; |
| |
| public JapaneseKatakanaStemFilter(TokenStream input, int minimumLength) { |
| super(input); |
| this.minimumKatakanaLength = minimumLength; |
| } |
| |
| public JapaneseKatakanaStemFilter(TokenStream input) { |
| this(input, DEFAULT_MINIMUM_LENGTH); |
| } |
| |
| @Override |
| public boolean incrementToken() throws IOException { |
| if (input.incrementToken()) { |
| if (!keywordAttr.isKeyword()) { |
| termAttr.setLength(stem(termAttr.buffer(), termAttr.length())); |
| } |
| return true; |
| } else { |
| return false; |
| } |
| } |
| |
| private int stem(char[] term, int length) { |
| if (length < minimumKatakanaLength) { |
| return length; |
| } |
| |
| if (! isKatakana(term, length)) { |
| return length; |
| } |
| |
| if (term[length - 1] == HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK) { |
| return length - 1; |
| } |
| |
| return length; |
| } |
| |
| private boolean isKatakana(char[] term, int length) { |
| for (int i = 0; i < length; i++) { |
| // NOTE: Test only identifies full-width characters -- half-widths are supported |
| if (Character.UnicodeBlock.of(term[i]) != Character.UnicodeBlock.KATAKANA) { |
| return false; |
| } |
| } |
| return true; |
| } |
| } |