com.google.common.cache
Class CacheLoader<K,V>

java.lang.Object
  com.google.common.cache.CacheLoader<K,V>

@Beta
@GwtCompatible(emulated=true)
public abstract class CacheLoader<K,V>
extends Object

Computes or retrieves values, based on a key, for use in populating a Cache.

Most implementations will only need to implement load(K). Other methods may be overridden as desired.

Since:

10.0

Author:

Charles Fry

Nested Class Summary

static class

CacheLoader.InvalidCacheLoadException Thrown to indicate that an invalid response was returned from a call to CacheLoader.

Constructor Summary

protected

CacheLoader() Constructor for use by subclasses.

Method Summary

static <K,V> CacheLoader<K,V>	from(Function<K,V> function) Returns a CacheLoader which creates values by applying a Function to the key.
static <V> CacheLoader<Object,V>	from(Supplier<V> supplier) Returns a CacheLoader which obtains values from a Supplier (independent of the key).
abstract V	load(K key) Computes or retrieves the value corresponding to key.
Map<K,V>	loadAll(Iterable<? extends K> keys) Computes or retrieves the values corresponding to keys.
ListenableFuture<V>	reload(K key, V oldValue) Computes or retrieves a replacement value corresponding to an already-cached key.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CacheLoader

protected CacheLoader()

Constructor for use by subclasses.

Method Detail

load

public abstract V load(K key)
                throws Exception

Computes or retrieves the value corresponding to key.

Parameters:

key - the non-null key whose value should be loaded

Returns:

the value associated with key; must not be null

Throws:

Exception

reload

@GwtIncompatible(value="Futures")
public ListenableFuture<V> reload(K key,
                                                       V oldValue)
                           throws Exception

Computes or retrieves a replacement value corresponding to an already-cached key. This method is called when an existing cache entry is refreshed by CacheBuilder.refreshAfterWrite(long, java.util.concurrent.TimeUnit), or through a call to Cache#refresh.

This implementation synchronously delegates to load(K). It is recommended that it be overridden with an asynchronous implementation when using CacheBuilder.refreshAfterWrite(long, java.util.concurrent.TimeUnit).

Note: all exceptions thrown by this method will be logged and then swallowed.

Parameters:

key - the non-null key whose value should be loaded

oldValue - the non-null old value corresponding to key

Returns:

the future new value associated with key; must not be null, must not return null

Throws:

Exception

Since:

11.0

loadAll

public Map<K,V> loadAll(Iterable<? extends K> keys)
                 throws Exception

Computes or retrieves the values corresponding to keys. This method is called by Cache#getAll.

If the returned map doesn't contain all requested keys then the entries it does contain will be cached, but getAll will throw an exception. If the returned map contains extra keys not present in keys then all returned entries will be cached, but only the entries for keys will be returned from getAll.

This method should be overriden when bulk retrieval is significantly more efficient than many individual lookups. Note that Cache#getAll will defer to individual calls to Cache.get(K, java.util.concurrent.Callable) if this method is not overriden.

Parameters:

keys - the unique, non-null keys whose values should be loaded

Returns:

a map from each key in keys to the value associated with that key; may not contain null values

Throws:

Exception

Since:

11.0

from

public static <K,V> CacheLoader<K,V> from(Function<K,V> function)

Returns a CacheLoader which creates values by applying a Function to the key.

from

public static <V> CacheLoader<Object,V> from(Supplier<V> supplier)

Returns a CacheLoader which obtains values from a Supplier (independent of the key).