lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUCollationAttributeFactory.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.TokenStream;
import org.apache.lucene.analysis.icu.tokenattributes.ICUCollatedTermAttributeImpl;
import org.apache.lucene.collation.CollationAttributeFactory;
import org.apache.lucene.util.AttributeFactory;

/**
 * Converts each token into its {@link com.ibm.icu.text.CollationKey}, and then encodes bytes 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 ICUCollationAttributeFactory to generate index
 * terms, do not use {@link CollationAttributeFactory} on the query side, or vice versa.
 *
 * <p>ICUCollationAttributeFactory is significantly faster and generates significantly shorter keys
 * than CollationAttributeFactory. 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.
 */
public class ICUCollationAttributeFactory
    extends AttributeFactory.StaticImplementationAttributeFactory<ICUCollatedTermAttributeImpl> {
  private final Collator collator;

  /**
   * Create an ICUCollationAttributeFactory, using {@link
   * TokenStream#DEFAULT_TOKEN_ATTRIBUTE_FACTORY} as the factory for all other attributes.
   *
   * @param collator CollationKey generator
   */
  public ICUCollationAttributeFactory(Collator collator) {
    this(TokenStream.DEFAULT_TOKEN_ATTRIBUTE_FACTORY, collator);
  }

  /**
   * Create an ICUCollationAttributeFactory, using the supplied Attribute Factory as the factory for
   * all other attributes.
   *
   * @param delegate Attribute Factory
   * @param collator CollationKey generator
   */
  public ICUCollationAttributeFactory(AttributeFactory delegate, Collator collator) {
    super(delegate, ICUCollatedTermAttributeImpl.class);
    this.collator = collator;
  }

  @Override
  public ICUCollatedTermAttributeImpl createInstance() {
    return new ICUCollatedTermAttributeImpl(collator);
  }
}