/*
* 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.
*/
using System;
using System.Collections.Generic;
using System.IO;
using System.Collections;
using System.Linq;
using Lucene.Net.Analysis;
using Version = Lucene.Net.Util.Version;
using Lucene.Net.Support.Compatibility;
namespace Lucene.Net.Analysis.AR
{
/*
* for Arabic.
*
* This analyzer implements light-stemming as specified by:
*
* Light Stemming for Arabic Information Retrieval
*
* http://www.mtholyoke.edu/~lballest/Pubs/arab_stem05.pdf
*
* The analysis package contains three primary components:
*
* - : Arabic orthographic normalization.
* - : Arabic light stemming
* - Arabic stop words file: a set of default Arabic stop words.
*
*
*/
public class ArabicAnalyzer : Analyzer
{
/*
* File containing default Arabic stopwords.
*
* Default stopword list is from http://members.unine.ch/jacques.savoy/clef/index.html
* The stopword list is BSD-Licensed.
*/
public static string DEFAULT_STOPWORD_FILE = "ArabicStopWords.txt";
/*
* Contains the stopwords used with the StopFilter.
*/
private readonly ISet stoptable;
/*
* The comment character in the stopwords file. All lines prefixed with this will be ignored
*
*/
[Obsolete("Use WordListLoader.GetWordSet(FileInfo, string) directly")]
public static string STOPWORDS_COMMENT = "#";
///
/// Returns an unmodifiable instance of the default stop-words set
///
/// Returns an unmodifiable instance of the default stop-words set
public static ISet GetDefaultStopSet()
{
return DefaultSetHolder.DEFAULT_STOP_SET;
}
private static class DefaultSetHolder
{
internal static ISet DEFAULT_STOP_SET;
static DefaultSetHolder()
{
try
{
DEFAULT_STOP_SET = LoadDefaultStopWordSet();
}
catch (System.IO.IOException)
{
// default set should always be present as it is part of the
// distribution (JAR)
throw new Exception("Unable to load default stopword set");
}
}
internal static ISet LoadDefaultStopWordSet()
{
using (StreamReader reader = new StreamReader(System.Reflection.Assembly.GetAssembly(typeof(ArabicAnalyzer)).GetManifestResourceStream("Lucene.Net.Analysis.AR." + DEFAULT_STOPWORD_FILE)))
{
return CharArraySet.UnmodifiableSet(CharArraySet.Copy(WordlistLoader.GetWordSet(reader, STOPWORDS_COMMENT)));
}
}
}
private Version matchVersion;
/*
* Builds an analyzer with the default stop words: .
*/
public ArabicAnalyzer(Version matchVersion)
: this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET)
{
}
///
/// Builds an analyzer with the given stop words.
///
/// Lucene compatibility version
/// a stopword set
public ArabicAnalyzer(Version matchVersion, ISet stopwords)
{
stoptable = CharArraySet.UnmodifiableSet(CharArraySet.Copy(stopwords));
this.matchVersion = matchVersion;
}
/*
* Builds an analyzer with the given stop words.
*/
[Obsolete("Use ArabicAnalyzer(Version, Set) instead")]
public ArabicAnalyzer(Version matchVersion, params string[] stopwords)
: this(matchVersion, StopFilter.MakeStopSet(stopwords))
{
}
/*
* Builds an analyzer with the given stop words.
*/
[Obsolete("Use ArabicAnalyzer(Version, Set) instead")]
public ArabicAnalyzer(Version matchVersion, IDictionary stopwords)
: this(matchVersion, stopwords.Keys.ToArray())
{
}
/*
* Builds an analyzer with the given stop words. Lines can be commented out using
*/
public ArabicAnalyzer(Version matchVersion, FileInfo stopwords)
: this(matchVersion, WordlistLoader.GetWordSet(stopwords, STOPWORDS_COMMENT))
{
}
/*
* Creates a which tokenizes all the text in the provided .
*
* A built from an filtered with
* , ,
* and .
*/
public override TokenStream TokenStream(string fieldName, TextReader reader)
{
TokenStream result = new ArabicLetterTokenizer(reader);
result = new LowerCaseFilter(result);
// the order here is important: the stopword list is not normalized!
result = new StopFilter(StopFilter.GetEnablePositionIncrementsVersionDefault(matchVersion), result, stoptable);
result = new ArabicNormalizationFilter(result);
result = new ArabicStemFilter(result);
return result;
}
private class SavedStreams
{
internal Tokenizer Source;
internal TokenStream Result;
};
/*
* Returns a (possibly reused) which tokenizes all the text
* in the provided .
*
* A built from an filtered with
* , ,
* and .
*/
public override TokenStream ReusableTokenStream(string fieldName, TextReader reader)
{
SavedStreams streams = (SavedStreams)PreviousTokenStream;
if (streams == null)
{
streams = new SavedStreams();
streams.Source = new ArabicLetterTokenizer(reader);
streams.Result = new LowerCaseFilter(streams.Source);
// the order here is important: the stopword list is not normalized!
streams.Result = new StopFilter(StopFilter.GetEnablePositionIncrementsVersionDefault(matchVersion),
streams.Result, stoptable);
streams.Result = new ArabicNormalizationFilter(streams.Result);
streams.Result = new ArabicStemFilter(streams.Result);
PreviousTokenStream = streams;
}
else
{
streams.Source.Reset(reader);
}
return streams.Result;
}
}
}