The diagram below shows the architecture of CCS.
The major classes and interfaces that form the Caching Content Store are:
- CachingContentStore: This is the main class that implements the ContentStore interface, and can therefore, be used anywhere that a ContentStore could be used. The CachingContentStore handles all the high level logic of interaction between the cache and the backing store, while the caching itself is provided by a collaborating ContentCache object.
- ContentCache: This class is responsible for putting items into and getting items from the cache. The single supplied implementation (ContentCacheImpl) for this class uses a lookup table to keep track of the files that are being managed by the cache, and a directory on the local file system to store the cached content files. The lookup table itself is an EhcacheAdapter instance.
- QuotaManagerStrategy: The quota managers implement this interface and control how the disk usage is consumed for cached content storage. SkyVault provides two implementations for this: UnlimitedQuotaStrategy (does not restrict disk usage, thereby effectively disabling the quota function) and StandardQuotaStrategy (attempts to keep usage below the maximum specified in bytes or MB).
The CachingContentStore class is highly configurable and many of its components could be exchanged for other implementations. For example, the lookup table could be easily replaced with a different implementation from the Ehcache-based class supplied, or the ContentCacheImpl could be replaced with an implementation that uses some alternative to the local file system for storage of cached content.
The cached content cleaner (CachedContentCleaner) periodically traverses the directory structure containing the cached content files and deletes the content files that are not in use by the cache. Files are considered not in use by the cache if they have no entry in the lookup table managed by ContentCacheImpl. The content cache cleaner is not a part of the architecture but is a helper object for ContentCacheImpl and allows it to operate more efficiently.