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Recipe: Tree Cache

Description​

A utility that attempts to keep all data from all children of a ZK path locally cached. This class will watch the ZK path, respond to update/create/delete events, pull down the data, etc. You can register a listener that will get notified when changes occur.

Participating Classes​

  • TreeCache
  • TreeCacheListener
  • TreeCacheEvent
  • ChildData

Creating a TreeCache​

// Parameters:
// client - the client
// path - path to watch
// cacheData - if true, node contents are cached in addition to the stat
public TreeCache(CuratorFramework client, String path, boolean cacheData);

General Usage​

The cache must be started by calling start(). Call close() when you are through with the cache.

At any time, call getCurrentChildren() to get the current state of the cache. Alternatively, call getCurrentData() to get the data for a given path that's being monitored.

You can also register to be notified when a change occurs by calling getListenable() and then:

// Add a change listener
// Parameters:
// listener - the listener
public void addListener(TreeCacheListener listener);

Error Handling​

TreeCache instances internally monitor a ConnectionStateListener. If the connection state changes, the cache will receive messages detailing the change.