com.github.benmanes.caffeine.cache

Interface CacheLoader<K,V>

All Superinterfaces:

AsyncCacheLoader<K,V>

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@ThreadSafe
 @FunctionalInterface
public interface CacheLoader<K,V>
extends AsyncCacheLoader<K,V>

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

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

Usage example:

   CacheLoader<Key, Graph> loader = key -> createExpensiveGraph(key);
   LoadingCache<Key, Graph> cache = Caffeine.newBuilder().build(loader);
 

Method Summary

Modifier and Type	Method and Description
default CompletableFuture<V>	asyncLoad(K key, Executor executor) Asynchronously computes or retrieves the value corresponding to key.
default CompletableFuture<Map<K,V>>	asyncLoadAll(Iterable<? extends K> keys, Executor executor) Asynchronously computes or retrieves the values corresponding to keys.
default CompletableFuture<V>	asyncReload(K key, V oldValue, Executor executor) Asynchronously computes or retrieves a replacement value corresponding to an already-cached key.
V	load(K key) Computes or retrieves the value corresponding to key.
default Map<K,V>	loadAll(Iterable<? extends K> keys) Computes or retrieves the values corresponding to keys.
default V	reload(K key, V oldValue) Computes or retrieves a replacement value corresponding to an already-cached key.

Method Detail

load

@CheckForNull
V load(@Nonnull
                     K key)
              throws Exception

Computes or retrieves the value corresponding to key.

Warning: loading must not attempt to update any other mappings of this cache.

Parameters:

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

Returns:

the value associated with key or null if not found

Throws:

Exception - or Error, in which case the mapping is unchanged

InterruptedException - if this method is interrupted. InterruptedException is treated like any other Exception in all respects except that, when it is caught, the thread's interrupt status is set

loadAll

@Nonnull
default Map<K,V> loadAll(@Nonnull
                                  Iterable<? extends K> keys)
                           throws Exception

Computes or retrieves the values corresponding to keys. This method is called by LoadingCache.getAll(java.lang.Iterable<? extends K>).

If the returned map doesn't contain all requested keys then the entries it does contain will be cached and getAll will return the partial results. 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 overridden when bulk retrieval is significantly more efficient than many individual lookups. Note that LoadingCache.getAll(java.lang.Iterable<? extends K>) will defer to individual calls to LoadingCache.get(K) if this method is not overridden.

Warning: loading must not attempt to update any other mappings of this cache.

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 - or Error, in which case the mappings are unchanged

InterruptedException - if this method is interrupted. InterruptedException is treated like any other Exception in all respects except that, when it is caught, the thread's interrupt status is set

asyncLoad

@Nonnull
default CompletableFuture<V> asyncLoad(@Nonnull
                                                K key,
                                                @Nonnull
                                                Executor executor)

Asynchronously computes or retrieves the value corresponding to key.

Specified by:

asyncLoad in interface AsyncCacheLoader<K,V>

Parameters:

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

executor - the executor that asynchronously loads the entry

Returns:

the future value associated with key

asyncLoadAll

@Nonnull
default CompletableFuture<Map<K,V>> asyncLoadAll(@Nonnull
                                                          Iterable<? extends K> keys,
                                                          @Nonnull
                                                          Executor executor)

Asynchronously computes or retrieves the values corresponding to keys. This method is called by AsyncLoadingCache.getAll(java.lang.Iterable<? extends K>).

If the returned map doesn't contain all requested keys then the entries it does contain will be cached and getAll will return the partial results. 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 overridden when bulk retrieval is significantly more efficient than many individual lookups. Note that AsyncLoadingCache.getAll(java.lang.Iterable<? extends K>) will defer to individual calls to AsyncLoadingCache.get(K, java.util.function.Function<? super K, ? extends V>) if this method is not overridden.

Specified by:

asyncLoadAll in interface AsyncCacheLoader<K,V>

Parameters:

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

executor - the executor that with asynchronously loads the entries

Returns:

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

reload

@CheckForNull
default V reload(@Nonnull
                               K key,
                               @Nonnull
                               V oldValue)
                        throws Exception

Computes or retrieves a replacement value corresponding to an already-cached key. If the replacement value is not found then the mapping will be removed if null is returned. This method is called when an existing cache entry is refreshed by Caffeine.refreshAfterWrite(long, java.util.concurrent.TimeUnit), or through a call to LoadingCache.refresh(K).

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 new value associated with key, or null if the mapping is to be removed

Throws:

Exception - or Error, in which case the mapping is unchanged

InterruptedException - if this method is interrupted. InterruptedException is treated like any other Exception in all respects except that, when it is caught, the thread's interrupt status is set

asyncReload

@Nonnull
default CompletableFuture<V> asyncReload(@Nonnull
                                                  K key,
                                                  @Nonnull
                                                  V oldValue,
                                                  @Nonnull
                                                  Executor executor)

Asynchronously computes or retrieves a replacement value corresponding to an already-cached key. If the replacement value is not found then the mapping will be removed if null is computed. This method is called when an existing cache entry is refreshed by Caffeine.refreshAfterWrite(long, java.util.concurrent.TimeUnit), or through a call to LoadingCache.refresh(K).

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

Specified by:

asyncReload in interface AsyncCacheLoader<K,V>

Parameters:

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

oldValue - the non-null old value corresponding to key

executor - the executor with which the entry is asynchronously loaded

Returns:

a future containing the new value associated with key, or containing null if the mapping is to be removed