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Lucene example source code file (ICUCollationKeyAnalyzer.java)

This example Lucene source code file (ICUCollationKeyAnalyzer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

collator, icucollationkeyanalyzer, icucollationkeyanalyzer, icucollationkeyfilter, io, ioexception, keywordtokenizer, override, reader, reader, savedstreams, savedstreams, tokenizer, tokenstream, tokenstream

The Lucene ICUCollationKeyAnalyzer.java source code

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;


/**
 * <p>
 *   Filters {@link KeywordTokenizer} with {@link ICUCollationKeyFilter}.
 * <p>
 *   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.
 * </p>
 * <p>
 *   <strong>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):
 * </p>
 * <ol>
 *   <li>
 *     Collator version - see {@link Collator#getVersion()}
 *   </li>
 *   <li>
 *     The collation strength used - see {@link Collator#setStrength(int)}
 *   </li>
 * </ol> 
 * <p>
 *   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.
 * </p>
 * <p>
 *   ICUCollationKeyAnalyzer is significantly faster and generates significantly
 *   shorter keys than CollationKeyAnalyzer.  See
 *   <a href="http://site.icu-project.org/charts/collation-icu4j-sun"
 *   >http://site.icu-project.org/charts/collation-icu4j-sun</a> for key
 *   generation timing and key length comparisons between ICU4J and
 *   java.text.Collator over several languages.
 * </p>
 */
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;
  }
}

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