lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUCollationKeyAnalyzer.java

/*
 * 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.
 */
package org.apache.lucene.analysis.icu;

import com.ibm.icu.text.Collator;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.core.KeywordTokenizer;
import org.apache.lucene.collation.CollationKeyAnalyzer;

/**
 * Configures {@link KeywordTokenizer} with {@link ICUCollationAttributeFactory}.
 *
 * <p>Converts the token into its {@link com.ibm.icu.text.CollationKey}, and then encodes the
 * CollationKey directly to allow it to be stored as an index term.
 *
 * <p><strong>WARNING:</strong> 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):
 *
 * <ol>
 *   <li>Collator version - see {@link Collator#getVersion()}
 *   <li>The collation strength used - see {@link Collator#setStrength(int)}
 * </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>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.
 *
 * @since 3.1
 */
public final class ICUCollationKeyAnalyzer extends Analyzer {
  private final ICUCollationAttributeFactory factory;

  /**
   * Create a new ICUCollationKeyAnalyzer, using the specified collator.
   *
   * @param collator CollationKey generator
   */
  public ICUCollationKeyAnalyzer(Collator collator) {
    this.factory = new ICUCollationAttributeFactory(collator);
  }

  @Override
  protected TokenStreamComponents createComponents(String fieldName) {
    KeywordTokenizer tokenizer =
        new KeywordTokenizer(factory, KeywordTokenizer.DEFAULT_BUFFER_SIZE);
    return new TokenStreamComponents(tokenizer, tokenizer);
  }
}