CacheInitializer.java from Texai at Krugle

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/*
 * CacheInitializer.java
 *
 * Created on January 30, 2007, 9:44 AM
 *
 * Description: Provides a static method to initialize the system caches.
 *
 * Copyright (C) 2007 Stephen L. Reed.
 *
 * This program is free software; you can redistribute it and/or modify it under the terms
 * of the GNU General Public License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program;
 * if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package org.texai.kb;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import net.jcip.annotations.ThreadSafe;
import net.sf.ehcache.Cache;
import net.sf.ehcache.CacheManager;

/** This class has static methods that initialize the ehcache caches used by the semantic annotation persistence framework.
 * The Constants class contains a list of cache names and initializeCaches() method iterates over those.  New caches may be added without
 * modifying this class.
 *
 * @author reed
 */
@ThreadSafe
public final class CacheInitializer {
  
  /** indicates whether the caches have been initialized */
  private static boolean areCachesInitialized = false;
  
  /** the cache access lock */
  private static Lock cacheAccessLock = new ReentrantLock();
  
  /** Creates a new instance of CacheInitializer. */
  protected CacheInitializer() {
    super();
  }
  
  /** Resets the system caches. */
  public static void resetCaches() {
    cacheAccessLock.lock();
    final CacheManager cacheManager = CacheManager.getInstance();
    for (final String namedCache : Constants.NAMED_CACHES) {
      if (cacheManager.cacheExists(namedCache)) {
        final Cache cache = cacheManager.getCache(namedCache);
        cache.removeAll();
        cache.clearStatistics();
      } else {
        cacheManager.addCache(namedCache);
      }
    }
    cacheAccessLock.unlock();
  }
  
  
  /** Initializes the system caches if not yet done. */
  public static void initializeCaches() {
    cacheAccessLock.lock();
    if (!areCachesInitialized) {
      areCachesInitialized = true;
      for (final String namedCache : Constants.NAMED_CACHES) {
        initializeCache(namedCache);
      }
    }
    cacheAccessLock.unlock();
  }
  
  /**
   * Resets the given cache.
   *
   * @param namedCache the name of the given cache
   */
  public static void resetCache(final String namedCache) {
    //preconditions
    assert namedCache != null : "namedCache must not be null";
    assert !namedCache.isEmpty() : "namedCache must not be empty";
    
    cacheAccessLock.lock();
    final CacheManager cacheManager = CacheManager.getInstance();
    if (cacheManager.cacheExists(namedCache)) {
      final Cache cache = cacheManager.getCache(namedCache);
      cache.removeAll();
      cache.clearStatistics();
    } else {
      cacheManager.addCache(namedCache);
    }
    cacheAccessLock.unlock();
  }
  
  /** Initializes the given cache.
   *
   * @param namedCache the name of the given cache
   */
  private static void initializeCache(final String namedCache) {
    //preconditions
    assert namedCache != null : "namedCache must not be null";
    assert !namedCache.isEmpty() : "namedCache must not be empty";
    
    CacheManager cacheManager = CacheManager.getInstance();
    if (!cacheManager.cacheExists(namedCache)) {
      cacheManager.addCache(namedCache);
    }
  }
  
}
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