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
   * <p>
   * http://www.apache.org/licenses/LICENSE-2.0
   * <p>
   * 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.atlas.utils;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.text.DateFormat;
  import java.util.Date;
  import java.util.LinkedHashMap;
  import java.util.Map;
  
  /**
   * Fixed size LRU Cache.
   *
   */
  public class LruCache<K, V> extends LinkedHashMap<K, V> {
      private static final Logger LOGGER = LoggerFactory.getLogger(LruCache.class.getName());
  
      private static final long serialVersionUID = 8715233786643882558L;
  
      /**
       * Specifies the number evictions that pass before a warning is logged.
       */
      private final int evictionWarningThrottle;
  
      // The maximum number of entries the cache holds.
      private final int capacity;
  
      // The number of evictions since the last warning was logged.
      private long evictionsSinceWarning;
  
      // When the last eviction warning was issued.
      private Date lastEvictionWarning = new Date();
  
      /**
       *
       * @param cacheSize The size of the cache.
       * @param evictionWarningThrottle The number evictions that pass before a warning is logged.
       */
      public LruCache(int cacheSize, int evictionWarningThrottle) {
          super(cacheSize, 0.75f, true);
  
          this.evictionWarningThrottle = evictionWarningThrottle;
          this.capacity                = cacheSize;
      }
  
      @Override
      protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
          if (size() > capacity) {
              evictionWarningIfNeeded();
  
              return true;
          }
  
          return false;
      }
  
      /**
       * Logs a warning if a threshold number of evictions has occurred since the
       * last warning.
       */
      private void evictionWarningIfNeeded() {
          // If not logging eviction warnings, just return.
          if (evictionWarningThrottle <= 0) {
              return;
          }
  
          evictionsSinceWarning++;
  
          if (evictionsSinceWarning >= evictionWarningThrottle) {
              DateFormat dateFormat = DateFormat.getDateTimeInstance();
  
              if (LOGGER.isInfoEnabled()) {
                  LOGGER.info("There have been {} evictions from the cache since {}", evictionsSinceWarning, dateFormat.format(lastEvictionWarning));
              }
  
              evictionsSinceWarning = 0;
              lastEvictionWarning   = new Date();
          }
      }
  }
  