code: public synchronized CacheEntry getEntry(String key) throws IOException {
          checkNotClosed();
          validateKey(key);
          CacheEntry cacheEntry = mLruEntries.get(key);
          if (cacheEntry == null) {
              return null;
          }
  
          trimToSize();
          addActionLog(ACTION_READ, cacheEntry);
          return cacheEntry;
      }
docs: Returns a {@link in.srain.cube.diskcache.CacheEntry} named {@code key}, or null if it doesn't
  exist is not currently readable. If a value is returned, it is moved to
  the head of the LRU queue.