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A module that is everything required to understands Druid Segments

There is a newer version: 30.0.1

/*
 * 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.druid.segment.serde;

import org.apache.druid.java.util.common.ISE;
import org.apache.druid.segment.column.TypeStrategies;

import javax.annotation.Nullable;
import java.util.concurrent.ConcurrentHashMap;

/**
 *  ComplexMetrics houses a mapping of serde names to affiliated ComplexMetricSerde objects.
 */
public class ComplexMetrics
{
  private static final ConcurrentHashMap COMPLEX_SERIALIZERS = new ConcurrentHashMap<>();

  @Nullable
  public static ComplexMetricSerde getSerdeForType(String type)
  {
    return COMPLEX_SERIALIZERS.get(type);
  }

  /**
   * Register a serde name -> ComplexMetricSerde mapping.
   *
   * 
   * If the specified serde key string is already used and the supplied ComplexMetricSerde is not of the same
   * type as the existing value in the map for said key, an ISE is thrown.
   * 
   *
   * @param type The serde name used as the key in the map.
   * @param serde The ComplexMetricSerde object to be associated with the 'type' in the map.
   */
  public static void registerSerde(String type, ComplexMetricSerde serde)
  {
    COMPLEX_SERIALIZERS.compute(type, (key, value) -> {
      if (value == null) {
        TypeStrategies.registerComplex(type, serde.getTypeStrategy());
        return serde;
      } else {
        if (!value.getClass().getName().equals(serde.getClass().getName())) {
          throw new ISE(
              "Incompatible serializer for type[%s] already exists. Expected [%s], found [%s].",
              key,
              serde.getClass().getName(),
              value.getClass().getName()
          );
        } else {
          return value;
        }
      }
    });
  }

  /**
   * Unregister a serde name -> ComplexMetricSerde mapping.
   *
   * If the specified serde key string is not in use, does nothing.
   *
   * Only expected to be used in tests.
   */
  public static void unregisterSerde(String type)
  {
    COMPLEX_SERIALIZERS.remove(type);
  }
}