lucene/analysis/common/src/java/org/apache/lucene/collation/CollationDocValuesField.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.collation;

import java.text.Collator;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.SortedDocValuesField;
import org.apache.lucene.util.BytesRef;

/**
 * Indexes collation keys as a single-valued {@link SortedDocValuesField}.
 *
 * <p>This is more efficient that {@link CollationKeyAnalyzer} if the field only has one value: no
 * uninversion is necessary to sort on the field, locale-sensitive range queries can still work via
 * {@code DocValuesRangeQuery}, and the underlying data structures built at index-time are likely
 * more efficient and use less memory than FieldCache.
 */
public final class CollationDocValuesField extends Field {
  private final String name;
  private final Collator collator;
  private final BytesRef bytes = new BytesRef();

  /**
   * Create a new ICUCollationDocValuesField.
   *
   * <p>NOTE: you should not create a new one for each document, instead just make one and reuse it
   * during your indexing process, setting the value via {@link #setStringValue(String)}.
   *
   * @param name field name
   * @param collator Collator for generating collation keys.
   */
  // TODO: can we make this trap-free? maybe just synchronize on the collator
  // instead?
  public CollationDocValuesField(String name, Collator collator) {
    super(name, SortedDocValuesField.TYPE);
    this.name = name;
    this.collator = (Collator) collator.clone();
    fieldsData = bytes; // so wrong setters cannot be called
  }

  @Override
  public String name() {
    return name;
  }

  @Override
  public void setStringValue(String value) {
    bytes.bytes = collator.getCollationKey(value).toByteArray();
    bytes.offset = 0;
    bytes.length = bytes.bytes.length;
  }
}