com.hazelcast.core

Interface MapLoader<K,V>

All Known Subinterfaces:

MapStore<K,V>

All Known Implementing Classes:

LatencyTrackingMapLoader, LatencyTrackingMapStore, MapStoreAdapter, MapStoreWrapper

public interface MapLoader<K,V>

Hazelcast distributed map implementation is an in-memory data store but it can be backed by any type of data store such as RDBMS, OODBMS, or simply a file based data store.

IMap.get(key) normally returns the value that is available in-memory. If the entry doesn't exist in-memory, Hazelcast returns null. If a Loader implementation is provided then, instead of returning null, Hazelcast will load the unknown entry by calling the implementation's load (key) or loadAll(keys) methods. Loaded entries will be placed into the distributed map and they will stay in-memory until they are explicitly removed or implicitly evicted (if eviction is configured).

Method Summary

Modifier and Type	Method and Description
V	load(K key) Loads the value of a given key.
Map<K,V>	loadAll(Collection<K> keys) Loads given keys.
Iterable<K>	loadAllKeys() Loads all of the keys from the store.

Method Detail

load

V load(K key)

Loads the value of a given key. If distributed map doesn't contain the value for the given key then Hazelcast will call implementation's load (key) method to obtain the value. Implementation can use any means of loading the given key; such as an O/R mapping tool, simple SQL or reading a file etc.

Parameters:

key, - cannot be null

Returns:

value of the key, value cannot be null

loadAll

Map<K,V> loadAll(Collection<K> keys)

Loads given keys. This is batch load operation so that implementation can optimize the multiple loads. For any key in the input keys, there should be a single mapping in the resulting map. Also the resulting map should not have any keys that are not part of the input keys. The given collection should not contain any null keys. The returned Map should not contain any null keys or values.

Parameters:

keys - keys of the values entries to load

Returns:

map of loaded key-value pairs.

loadAllKeys

Iterable<K> loadAllKeys()

Loads all of the keys from the store. The returned Iterable may return the keys lazily by loading them in batches. The Iterator of this Iterable may implement the Closeable interface in which case it will be closed once iteration is over. This is intended for releasing resources such as closing a JDBC result set. The returned Iterable should not contain any null keys.

Returns:

all the keys. Keys inside the Iterable cannot be null.