content: /**
   * 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.apex.malhar.contrib.enrich;
  
  import org.apache.apex.malhar.lib.db.cache.CacheManager;
  import org.apache.hadoop.classification.InterfaceStability;
  
  /**
   * Null Values Cache Manager. Using this NULL entries can be specified explicitly.
   *
   * @since 3.4.0
   */
  @InterfaceStability.Evolving
  public class NullValuesCacheManager extends CacheManager
  {
  
    private static final NullObject NULL = new NullObject();
  
    @Override
    public Object get(Object key)
    {
      Object primaryVal = primary.get(key);
      if (primaryVal != null) {
        if (primaryVal == NULL) {
          return null;
        }
  
        return primaryVal;
      }
  
      Object backupVal = backup.get(key);
      if (backupVal != null) {
        primary.put(key, backupVal);
      } else {
        primary.put(key, NULL);
      }
  
      return backupVal;
    }
  
    private static class NullObject
    {
    }
  }
  
  