package com.foxinmy.weixin4j.cache;
   
   import java.util.concurrent.TimeUnit;
   import java.util.concurrent.locks.ReentrantLock;
   
   import com.foxinmy.weixin4j.exception.WeixinException;
   
   /**
    * 缓存管理类
   *
   * @className CacheManager
   * @author jinyu(foxinmy@gmail.com)
   * @date 2016年5月27日
   * @since JDK 1.7
   * @see
   */
  public class CacheManager<T extends Cacheable> {
      protected final CacheCreator<T> cacheCreator;
      protected final CacheStorager<T> cacheStorager;
      private final ReentrantLock lock = new ReentrantLock();
  
      public CacheManager(CacheCreator<T> cacheCreator, CacheStorager<T> cacheStorager) {
          this.cacheCreator = cacheCreator;
          this.cacheStorager = cacheStorager;
      }
  
      /**
       * 获取缓存对象
       *
       * @return 缓存对象
       * @throws WeixinException
       */
      public T getCache() throws WeixinException {
          String cacheKey = cacheCreator.key();
          T cache = cacheStorager.lookup(cacheKey);
          try {
              if (cache == null && lock.tryLock(3, TimeUnit.SECONDS)) {
                  try {
                      cache = cacheStorager.lookup(cacheKey);
                      if (cache == null) {
                          cache = cacheCreator.create();
                          cacheStorager.caching(cacheKey, cache);
                      }
                  } finally {
                      lock.unlock();
                  }
              }
          } catch (InterruptedException e) {
              throw new WeixinException("get cache error on lock", e);
          }
          return cache;
      }
  
      /**
       * 刷新缓存对象
       *
       * @return 缓存对象
       * @throws WeixinException
       */
      public T refreshCache() throws WeixinException {
          String cacheKey = cacheCreator.key();
          T cache = cacheCreator.create();
          cacheStorager.caching(cacheKey, cache);
          return cache;
      }
  
      /**
       * 移除缓存
       *
       * @return 被移除的缓存对象
       */
      public T evictCache() {
          String cacheKey = cacheCreator.key();
          return cacheStorager.evict(cacheKey);
      }
  
      /**
       * 清除所有的缓存(<font color="red">请慎重</font>)
       */
      public void clearCache() {
          cacheStorager.clear();
      }
  }