GridCacheForStream class

This class contains the cache operations for GridJs. User shall implement his own business logic for storage based on it..

The GridCacheForStream type exposes the following members:

Method	Description
`save_stream(self, s, uid)`	Implements this method to save cache,save the stream to the cache with the key uid.
`load_stream(self, uid)`	Implements this method to load cache with the key uid,return the stream from the cache.
`is_existed(self, uid)`	Checks whether the cache with uid is existed
`get_file_url(self, uid)`	Implements this method to get the file url from the cache.