A CacheLoader can be used to enforce node passivation and activation on eviction in a TreeCache.

Cache Passivation is the process of removing an object from in-memory cache and writing it to a secondary data store (e.g., file system, database) on eviction. Cache Activation is the process of restoring an object from the data store into the in-memory cache when it's needed to be used. In both cases, the configured CacheLoader will be used to read from the data store and write to the data store.

When the eviction policy in effect calls evict() to evict a node from the cache, if passivation is enabled, a notification that the node is being passivated will be emitted to the tree cache listeners and the node and its children will be stored in the cache loader store. When a user calls get() on a node that was evicted earlier, the node is loaded (lazy loaded) from the cache loader store into the in-memory cache. When the node and its children have been loaded, they're removed from the cache loader and a notification is emitted to the tree cache listeners that the node has been activated.

To enable cache passivation/activation, you can set passivation to true. The default is false. You set it via the XML cache configuration file. The XML above shows the passivation element when configuring a cache loader. When passivation is used, only the first cache loader configured is used. All others are ignored.