| using Lucene.Net.Analysis.TokenAttributes; |
| using System.Text.RegularExpressions; |
| |
| namespace Lucene.Net.Analysis.Ja |
| { |
| /* |
| * 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. |
| */ |
| |
| /// <summary> |
| /// A <see cref="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). |
| /// </summary> |
| /// <remarks> |
| /// Note that only full-width katakana characters are supported. Please use a |
| /// <see cref="Cjk.CJKWidthFilter"/> to convert half-width |
| /// katakana to full-width before using this filter. |
| /// <para/> |
| /// In order to prevent terms from being stemmed, use an instance of |
| /// <see cref="Miscellaneous.SetKeywordMarkerFilter"/> |
| /// or a custom <see cref="TokenFilter"/> that sets the <see cref="IKeywordAttribute"/> |
| /// before this <see cref="TokenStream"/>. |
| /// </remarks> |
| public sealed class JapaneseKatakanaStemFilter : TokenFilter |
| { |
| public const int DEFAULT_MINIMUM_LENGTH = 4; |
| private const char HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK = '\u30fc'; |
| |
| private readonly ICharTermAttribute termAttr; |
| private readonly IKeywordAttribute keywordAttr; |
| private readonly int minimumKatakanaLength; |
| |
| private readonly static Regex katakanaPattern = new Regex(@"\p{IsKatakana}", RegexOptions.Compiled | RegexOptions.CultureInvariant); |
| |
| public JapaneseKatakanaStemFilter(TokenStream input, int minimumLength) |
| : base(input) |
| { |
| this.minimumKatakanaLength = minimumLength; |
| this.termAttr = AddAttribute<ICharTermAttribute>(); |
| this.keywordAttr = AddAttribute<IKeywordAttribute>(); |
| } |
| |
| public JapaneseKatakanaStemFilter(TokenStream input) |
| : this(input, DEFAULT_MINIMUM_LENGTH) |
| { |
| } |
| |
| public override bool IncrementToken() |
| { |
| if (m_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 static bool IsKatakana(char[] term, int length) // LUCENENET: CA1822: Mark members as static |
| { |
| for (int i = 0; i < length; i++) |
| { |
| // NOTE: Test only identifies full-width characters -- half-widths are supported |
| if (!katakanaPattern.IsMatch(term[i].ToString())) |
| { |
| return false; |
| } |
| } |
| return true; |
| } |
| } |
| } |