StandardTokenizer.cs

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 * 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
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using System;
using Lucene.Net.Analysis.Tokenattributes;
using Lucene.Net.Util;
using CharReader = Lucene.Net.Analysis.CharReader;
using Token = Lucene.Net.Analysis.Token;
using Tokenizer = Lucene.Net.Analysis.Tokenizer;
using AttributeSource = Lucene.Net.Util.AttributeSource;
using Version = Lucene.Net.Util.Version;

namespace Lucene.Net.Analysis.Standard
{
    
    /// <summary>A grammar-based tokenizer constructed with JFlex
    /// 
    /// <p/> This should be a good tokenizer for most European-language documents:
    /// 
    /// <list type="bullet">
    /// <item>Splits words at punctuation characters, removing punctuation. However, a 
    /// dot that's not followed by whitespace is considered part of a token.</item>
    /// <item>Splits words at hyphens, unless there's a number in the token, in which case
    /// the whole token is interpreted as a product number and is not split.</item>
    /// <item>Recognizes email addresses and internet hostnames as one token.</item>
    /// </list>
    /// 
    /// <p/>Many applications have specific tokenizer needs.  If this tokenizer does
    /// not suit your application, please consider copying this source code
    /// directory to your project and maintaining your own grammar-based tokenizer.
    /// 
    /// <a name="version"/>
    /// <p/>
    /// You must specify the required <see cref="Version" /> compatibility when creating
    /// StandardAnalyzer:
    /// <list type="bullet">
    /// <item>As of 2.4, Tokens incorrectly identified as acronyms are corrected (see
    /// <a href="https://issues.apache.org/jira/browse/LUCENE-1068">LUCENE-1608</a></item>
    /// </list>
    /// </summary>
    
    public sealed class StandardTokenizer:Tokenizer
    {
        private void  InitBlock()
        {
            maxTokenLength = StandardAnalyzer.DEFAULT_MAX_TOKEN_LENGTH;
        }
        /// <summary>A private instance of the JFlex-constructed scanner </summary>
        private StandardTokenizerImpl scanner;
        
        public const int ALPHANUM   = 0;
        public const int APOSTROPHE = 1;
        public const int ACRONYM    = 2;
        public const int COMPANY    = 3;
        public const int EMAIL      = 4;
        public const int HOST       = 5;
        public const int NUM        = 6;
        public const int CJ         = 7;
        
        /// <deprecated> this solves a bug where HOSTs that end with '.' are identified
        /// as ACRONYMs.
        /// </deprecated>
        [Obsolete("this solves a bug where HOSTs that end with '.' are identified as ACRONYMs.")]
        public const int ACRONYM_DEP = 8;
        
        /// <summary>String token types that correspond to token type int constants </summary>
        public static readonly System.String[] TOKEN_TYPES = new System.String[]{"<ALPHANUM>", "<APOSTROPHE>", "<ACRONYM>", "<COMPANY>", "<EMAIL>", "<HOST>", "<NUM>", "<CJ>", "<ACRONYM_DEP>"};
        
        private bool replaceInvalidAcronym;
        
        private int maxTokenLength;

        /// <summary>Set the max allowed token length.  Any token longer
        /// than this is skipped. 
        /// </summary>
        public int MaxTokenLength
        {
            get { return maxTokenLength; }
            set { this.maxTokenLength = value; }
        }

        /// <summary> Creates a new instance of the
        /// <see cref="Lucene.Net.Analysis.Standard.StandardTokenizer" />. Attaches
        /// the <c>input</c> to the newly created JFlex scanner.
        /// 
        /// </summary>
        /// <param name="matchVersion"></param>
        /// <param name="input">The input reader
        /// 
        /// See http://issues.apache.org/jira/browse/LUCENE-1068
        /// </param>
        public StandardTokenizer(Version matchVersion, System.IO.TextReader input):base()
        {
            InitBlock();
            this.scanner = new StandardTokenizerImpl(input);
            Init(input, matchVersion);
        }

        /// <summary> Creates a new StandardTokenizer with a given <see cref="AttributeSource" />.</summary>
        public StandardTokenizer(Version matchVersion, AttributeSource source, System.IO.TextReader input):base(source)
        {
            InitBlock();
            this.scanner = new StandardTokenizerImpl(input);
            Init(input, matchVersion);
        }
        
        /// <summary> Creates a new StandardTokenizer with a given
        /// <see cref="Lucene.Net.Util.AttributeSource.AttributeFactory" />
        /// </summary>
        public StandardTokenizer(Version matchVersion, AttributeFactory factory, System.IO.TextReader input):base(factory)
        {
            InitBlock();
            this.scanner = new StandardTokenizerImpl(input);
            Init(input, matchVersion);
        }
        
        private void  Init(System.IO.TextReader input, Version matchVersion)
        {
            if (matchVersion.OnOrAfter(Version.LUCENE_24))
            {
                replaceInvalidAcronym = true;
            }
            else
            {
                replaceInvalidAcronym = false;
            }
            this.input = input;
            termAtt = AddAttribute<ITermAttribute>();
            offsetAtt = AddAttribute<IOffsetAttribute>();
            posIncrAtt = AddAttribute<IPositionIncrementAttribute>();
            typeAtt = AddAttribute<ITypeAttribute>();
        }
        
        // this tokenizer generates three attributes:
        // offset, positionIncrement and type
        private ITermAttribute termAtt;
        private IOffsetAttribute offsetAtt;
        private IPositionIncrementAttribute posIncrAtt;
        private ITypeAttribute typeAtt;
        
        ///<summary>
        /// (non-Javadoc)
        /// <see cref="Lucene.Net.Analysis.TokenStream.IncrementToken()" />
        ///</summary>
        public override bool IncrementToken()
        {
            ClearAttributes();
            int posIncr = 1;
            
            while (true)
            {
                int tokenType = scanner.GetNextToken();
                
                if (tokenType == StandardTokenizerImpl.YYEOF)
                {
                    return false;
                }
                
                if (scanner.Yylength() <= maxTokenLength)
                {
                    posIncrAtt.PositionIncrement = posIncr;
                    scanner.GetText(termAtt);
                    int start = scanner.Yychar();
                    offsetAtt.SetOffset(CorrectOffset(start), CorrectOffset(start + termAtt.TermLength()));
                    // This 'if' should be removed in the next release. For now, it converts
                    // invalid acronyms to HOST. When removed, only the 'else' part should
                    // remain.
                    if (tokenType == StandardTokenizerImpl.ACRONYM_DEP)
                    {
                        if (replaceInvalidAcronym)
                        {
                            typeAtt.Type = StandardTokenizerImpl.TOKEN_TYPES[StandardTokenizerImpl.HOST];
                            termAtt.SetTermLength(termAtt.TermLength() - 1); // remove extra '.'
                        }
                        else
                        {
                            typeAtt.Type = StandardTokenizerImpl.TOKEN_TYPES[StandardTokenizerImpl.ACRONYM];
                        }
                    }
                    else
                    {
                        typeAtt.Type = StandardTokenizerImpl.TOKEN_TYPES[tokenType];
                    }
                    return true;
                }
                // When we skip a too-long term, we still increment the
                // position increment
                else
                    posIncr++;
            }
        }
        
        public override void  End()
        {
            // set final offset
            int finalOffset = CorrectOffset(scanner.Yychar() + scanner.Yylength());
            offsetAtt.SetOffset(finalOffset, finalOffset);
        }
        
        public override void  Reset(System.IO.TextReader reader)
        {
            base.Reset(reader);
            scanner.Reset(reader);
        }
        
        /// <summary>
        /// Remove in 3.X and make true the only valid value
        /// See https://issues.apache.org/jira/browse/LUCENE-1068
        /// </summary>
        /// <param name="replaceInvalidAcronym">Set to true to replace mischaracterized acronyms as HOST.
        /// </param>
        [Obsolete("Remove in 3.X and make true the only valid value. See https://issues.apache.org/jira/browse/LUCENE-1068")]
        public void  SetReplaceInvalidAcronym(bool replaceInvalidAcronym)
        {
            this.replaceInvalidAcronym = replaceInvalidAcronym;
        }
    }
}