Analyzer.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
 * limitations under the License.
 */

using System;
using Lucene.Net.Documents;
using Lucene.Net.Store;
using Lucene.Net.Util;

namespace Lucene.Net.Analysis
{
    /// <summary>An Analyzer builds TokenStreams, which analyze text.  It thus represents a
    /// policy for extracting index terms from text.
    /// <p/>
    /// Typical implementations first build a Tokenizer, which breaks the stream of
    /// characters from the Reader into raw Tokens.  One or more TokenFilters may
    /// then be applied to the output of the Tokenizer.
    /// </summary>
    public abstract class Analyzer : IDisposable
    {
        /// <summary>Creates a TokenStream which tokenizes all the text in the provided
        /// Reader.  Must be able to handle null field name for
        /// backward compatibility.
        /// </summary>
        public abstract TokenStream TokenStream(String fieldName, System.IO.TextReader reader);
        
        /// <summary>Creates a TokenStream that is allowed to be re-used
        /// from the previous time that the same thread called
        /// this method.  Callers that do not need to use more
        /// than one TokenStream at the same time from this
        /// analyzer should use this method for better
        /// performance.
        /// </summary>
        public virtual TokenStream ReusableTokenStream(String fieldName, System.IO.TextReader reader)
        {
            return TokenStream(fieldName, reader);
        }
        
        private CloseableThreadLocal<Object> tokenStreams = new CloseableThreadLocal<Object>();
        private bool isDisposed;

        /// <summary>Used by Analyzers that implement reusableTokenStream
        /// to retrieve previously saved TokenStreams for re-use
        /// by the same thread. 
        /// </summary>
        protected internal virtual object PreviousTokenStream
        {
            get
            {
                if (tokenStreams == null)
                {
                    throw new AlreadyClosedException("this Analyzer is closed");
                }
                return tokenStreams.Get();
            }
            set
            {
                if (tokenStreams == null)
                {
                    throw new AlreadyClosedException("this Analyzer is closed");
                }
                tokenStreams.Set(value);
            }
        }

        [Obsolete()]
        protected internal bool overridesTokenStreamMethod = false;
        
        /// <deprecated> This is only present to preserve
        /// back-compat of classes that subclass a core analyzer
        /// and override tokenStream but not reusableTokenStream 
        /// </deprecated>
        /// <summary>
        /// Java uses Class&lt;? extends Analyer&gt; to constrain <typeparamref name="TClass"/> to
        /// only Types that inherit from Analyzer.  C# does not have a generic type class,
        /// ie Type&lt;t&gt;.  The method signature stays the same, and an exception may
        /// still be thrown, if the method doesn't exist.
        /// </summary>
        [Obsolete("This is only present to preserve back-compat of classes that subclass a core analyzer and override tokenStream but not reusableTokenStream ")]
        protected internal virtual void SetOverridesTokenStreamMethod<TClass>()
            where TClass : Analyzer
        {
            try
            {
                System.Reflection.MethodInfo m = this.GetType().GetMethod("TokenStream", new[] { typeof(string), typeof(System.IO.TextReader) });
                overridesTokenStreamMethod = m.DeclaringType != typeof(TClass);
            }
            catch (MethodAccessException)
            {
                // can't happen, as baseClass is subclass of Analyzer
                overridesTokenStreamMethod = false;
            }
        }
        
        
        /// <summary> Invoked before indexing a Fieldable instance if
        /// terms have already been added to that field.  This allows custom
        /// analyzers to place an automatic position increment gap between
        /// Fieldable instances using the same field name.  The default value
        /// position increment gap is 0.  With a 0 position increment gap and
        /// the typical default token position increment of 1, all terms in a field,
        /// including across Fieldable instances, are in successive positions, allowing
        /// exact PhraseQuery matches, for instance, across Fieldable instance boundaries.
        /// 
        /// </summary>
        /// <param name="fieldName">Fieldable name being indexed.
        /// </param>
        /// <returns> position increment gap, added to the next token emitted from <see cref="TokenStream(String,System.IO.TextReader)" />
        /// </returns>
        public virtual int GetPositionIncrementGap(String fieldName)
        {
            return 0;
        }
        
        /// <summary> Just like <see cref="GetPositionIncrementGap" />, except for
        /// Token offsets instead.  By default this returns 1 for
        /// tokenized fields and, as if the fields were joined
        /// with an extra space character, and 0 for un-tokenized
        /// fields.  This method is only called if the field
        /// produced at least one token for indexing.
        /// 
        /// </summary>
        /// <param name="field">the field just indexed
        /// </param>
        /// <returns> offset gap, added to the next token emitted from <see cref="TokenStream(String,System.IO.TextReader)" />
        /// </returns>
        public virtual int GetOffsetGap(IFieldable field)
        {
            return field.IsTokenized ? 1 : 0;
        }

        /// <summary>Frees persistent resources used by this Analyzer </summary>
        public void  Close()
        {
            Dispose();
        }

        public virtual void Dispose()
        {
            Dispose(true);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (isDisposed) return;

            if (disposing)
            {
                if (tokenStreams != null)
                {
                    tokenStreams.Close();
                    tokenStreams = null;
                }
            }
            isDisposed = true;
        }
    }
}