code: private long getDataSize(final CacheKey key) throws UnknownDataSizeException
     {
        Long size = SecurityHelper.doPrivilegedAction(new PrivilegedAction<Long>()
        {
           public Long run()
           {
              return (Long)cache.withFlags(Flag.FORCE_WRITE_LOCK).get(key);
           }
        });
        if (size == null)
        {
           throw new UnknownDataSizeException("Data size is unknown");
        }
  
        return size;
     }
docs: Returns data size value otherwise throws {@link UnknownDataSizeException}.