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/*
 * Based on JUEL 2.2.1 code, 2006-2009 Odysseus Software GmbH
 *
 * Licensed 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.activiti.engine.impl.juel;

import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.Map.Entry;

/**
 * Simple (thread-safe) LRU cache. After the cache size reached a certain limit, the least recently used entry is removed, when adding a new entry.
 * 
 * @author Christoph Beck
 */
public final class Cache implements TreeCache {
  private final Map primary;
  private final Map secondary;

  /**
   * Constructor. Use a {@link WeakHashMap} as secondary map.
   * 
   * @param size
   *          maximum primary cache size
   */
  public Cache(int size) {
    this(size, new WeakHashMap());
  }

  /**
   * Constructor. If the least recently used entry is removed from the primary cache, it is added to the secondary map.
   * 
   * @param size
   *          maximum primary cache size
   * @param secondary
   *          the secondary map (may be null)
   */
  @SuppressWarnings("serial")
  public Cache(final int size, Map secondary) {
    this.primary = Collections.synchronizedMap(new LinkedHashMap(16, 0.75f, true) {
      @Override
      protected boolean removeEldestEntry(Entry eldest) {
        if (size() > size) {
          if (Cache.this.secondary != null) { // move to secondary
                                              // cache
            Cache.this.secondary.put(eldest.getKey(), eldest.getValue());
          }
          return true;
        }
        return false;
      }
    });
    this.secondary = secondary == null ? null : Collections.synchronizedMap(secondary);
  }

  public Tree get(String expression) {
    if (secondary == null) {
      return primary.get(expression);
    } else {
      Tree tree = primary.get(expression);
      if (tree == null) {
        tree = secondary.get(expression);
      }
      return tree;
    }
  }

  public void put(String expression, Tree tree) {
    primary.put(expression, tree);
  }
}