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Provides integration with ICU (International Components for Unicode) for stronger Unicode and internationalization support.
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package org.apache.lucene.collation;

/**
 * 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.
 */


import com.ibm.icu.text.Collator;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.KeywordTokenizer;
import org.apache.lucene.analysis.Tokenizer;

import org.apache.lucene.collation.CollationKeyAnalyzer; // javadocs

import java.io.Reader;
import java.io.IOException;


/**
 * 
 *   Filters {@link KeywordTokenizer} with {@link ICUCollationKeyFilter}.
 * 

 *   Converts the token into its {@link com.ibm.icu.text.CollationKey}, and
 *   then encodes the CollationKey with 
 *   {@link org.apache.lucene.util.IndexableBinaryStringTools}, to allow it to
 *   be stored as an index term.
 * 
 * 
 *   WARNING: Make sure you use exactly the same Collator at
 *   index and query time -- CollationKeys are only comparable when produced by
 *   the same Collator.  {@link com.ibm.icu.text.RuleBasedCollator}s are 
 *   independently versioned, so it is safe to search against stored
 *   CollationKeys if the following are exactly the same (best practice is
 *   to store this information with the index and check that they remain the
 *   same at query time):
 * 
 * 
 *   
 *     Collator version - see {@link Collator#getVersion()}
 *   
 *   
 *     The collation strength used - see {@link Collator#setStrength(int)}
 *   
 *  
 * 
 *   CollationKeys generated by ICU Collators are not compatible with those
 *   generated by java.text.Collators.  Specifically, if you use 
 *   ICUCollationKeyAnalyzer to generate index terms, do not use 
 *   {@link CollationKeyAnalyzer} on the query side, or vice versa.
 * 
 * 
 *   ICUCollationKeyAnalyzer is significantly faster and generates significantly
 *   shorter keys than CollationKeyAnalyzer.  See
 *   http://site.icu-project.org/charts/collation-icu4j-sun for key
 *   generation timing and key length comparisons between ICU4J and
 *   java.text.Collator over several languages.
 * 
 */
public final class ICUCollationKeyAnalyzer extends Analyzer {
  private Collator collator;

  public ICUCollationKeyAnalyzer(Collator collator) {
    this.collator = collator;
  }

  @Override
  public TokenStream tokenStream(String fieldName, Reader reader) {
    TokenStream result = new KeywordTokenizer(reader);
    result = new ICUCollationKeyFilter(result, collator);
    return result;
  }
  
  private class SavedStreams {
    Tokenizer source;
    TokenStream result;
  }
  
  @Override
  public TokenStream reusableTokenStream(String fieldName, Reader reader) 
    throws IOException {
    
    SavedStreams streams = (SavedStreams)getPreviousTokenStream();
    if (streams == null) {
      streams = new SavedStreams();
      streams.source = new KeywordTokenizer(reader);
      streams.result = new ICUCollationKeyFilter(streams.source, collator);
      setPreviousTokenStream(streams);
    } else {
      streams.source.reset(reader);
    }
    return streams.result;
  }
}