Module com.github.benmanes.caffeine
Package 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.
    @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 Detail

      • load

        @Nullable V load​(K key)
          throws Exception
        Computes or retrieves the value corresponding to key.

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

        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

        default Map<? extends K,​? extends V> loadAll​(Set<? 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 mappings of this cache directly.

        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

        default CompletableFuture<? extends V> asyncLoad​(K key,
                                                 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

        default CompletableFuture<? extends Map<? extends K,​? extends V>> asyncLoadAll​(Set<? extends K> keys,
                                                                                     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) if this method is not overridden.

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

        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

        default @Nullable V reload​(K key,
                           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(java.time.Duration), or through a call to LoadingCache.refresh(K).

        Warning: loading must not attempt to update any mappings of this cache directly or block waiting for other cache operations to complete.

        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

        default CompletableFuture<? extends V> asyncReload​(K key,
                                                   V oldValue,
                                                   Executor executor)
                                            throws Exception
        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(java.time.Duration), or through a call to LoadingCache.refresh(K).

        Warning: loading must not attempt to update any mappings of this cache directly or block waiting for other cache operations to complete.

        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
        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

      • bulk

        @CheckReturnValue
static <K,​V> CacheLoader<K,​V> bulk​(Function<? super Set<? extends K>,​? extends Map<? extends K,​? extends V>> mappingFunction)
        Returns a cache loader that delegates to the supplied mapping function for retrieving the values. Note that load(K) will silently discard any additional mappings loaded when retrieving the key prior to returning to the value to the cache.

        Usage example: 

        
   CacheLoader<Key, Graph> loader = CacheLoader.bulk(keys -> createExpensiveGraphs(keys));
   LoadingCache<Key, Graph> cache = Caffeine.newBuilder().build(loader);
        Type Parameters:
        K - the key type
        V - the value type
        Parameters:
        mappingFunction - the function to compute the values
        Returns:
        a cache loader that delegates to the supplied mappingFunction
        Throws:
        NullPointerException - if the mappingFunction is null