com.google.common.cache

Interface LoadingCache<K,V>

All Superinterfaces:

Cache<K,V>, Function<K,V>

All Known Implementing Classes:

AbstractLoadingCache, ForwardingLoadingCache, ForwardingLoadingCache.SimpleForwardingLoadingCache

@Beta
@GwtCompatible
public interface LoadingCache<K,V>
extends Cache<K,V>, Function<K,V>

A semi-persistent mapping from keys to values. Values are automatically loaded by the cache, and are stored in the cache until either evicted or manually invalidated.

Implementations of this interface are expected to be thread-safe, and can be safely accessed by multiple concurrent threads.

When evaluated as a Function, a cache yields the same result as invoking getUnchecked(K).

Note that while this class is still annotated as Beta, the API is frozen from a consumer's standpoint. In other words existing methods are all considered non-Beta and won't be changed without going through an 18 month deprecation cycle; however new methods may be added at any time.

Since:

11.0

Author:

Charles Fry

Method Summary

Methods

Modifier and Type	Method and Description
V	apply(K key) Deprecated. Provided to satisfy the Function interface; use get(K) or getUnchecked(K) instead.
ConcurrentMap<K,V>	asMap() Returns a view of the entries stored in this cache as a thread-safe map.
V	get(K key) Returns the value associated with key in this cache, first loading that value if necessary.
ImmutableMap<K,V>	getAll(Iterable<? extends K> keys) Returns a map of the values associated with keys, creating or retrieving those values if necessary.
V	getUnchecked(K key) Returns the value associated with key in this cache, first loading that value if necessary.
void	refresh(K key) Loads a new value for key key, possibly asynchronously.

Methods inherited from interface com.google.common.cache.Cache

cleanUp, get, getAllPresent, getIfPresent, invalidate, invalidateAll, invalidateAll, put, putAll, size, stats

Methods inherited from interface com.google.common.base.Function

equals

Method Detail

get

V get(K key)
      throws ExecutionException

Returns the value associated with key in this cache, first loading that value if necessary. No observable state associated with this cache is modified until loading completes.

If another call to get(K) or getUnchecked(K) is currently loading the value for key, simply waits for that thread to finish and returns its loaded value. Note that multiple threads can concurrently load values for distinct keys.

Caches loaded by a CacheLoader will call CacheLoader.load(K) to load new values into the cache. Newly loaded values are added to the cache using Cache.asMap().putIfAbsent after loading has completed; if another value was associated with key while the new value was loading then a removal notification will be sent for the new value.

If the cache loader associated with this cache is known not to throw checked exceptions, then prefer getUnchecked(K) over this method.

Throws:

ExecutionException - if a checked exception was thrown while loading the value. (ExecutionException is thrown even if computation was interrupted by an InterruptedException.)

UncheckedExecutionException - if an unchecked exception was thrown while loading the value

ExecutionError - if an error was thrown while loading the value

getUnchecked

V getUnchecked(K key)

Returns the value associated with key in this cache, first loading that value if necessary. No observable state associated with this cache is modified until loading completes. Unlike get(K), this method does not throw a checked exception, and thus should only be used in situations where checked exceptions are not thrown by the cache loader.

If another call to get(K) or getUnchecked(K) is currently loading the value for key, simply waits for that thread to finish and returns its loaded value. Note that multiple threads can concurrently load values for distinct keys.

Caches loaded by a CacheLoader will call CacheLoader.load(K) to load new values into the cache. Newly loaded values are added to the cache using Cache.asMap().putIfAbsent after loading has completed; if another value was associated with key while the new value was loading then a removal notification will be sent for the new value.

Warning: this method silently converts checked exceptions to unchecked exceptions, and should not be used with cache loaders which throw checked exceptions. In such cases use get(K) instead.

Throws:

UncheckedExecutionException - if an exception was thrown while loading the value. (As explained in the last paragraph above, this should be an unchecked exception only.)

ExecutionError - if an error was thrown while loading the value

getAll

ImmutableMap<K,V> getAll(Iterable<? extends K> keys)
                         throws ExecutionException

Returns a map of the values associated with keys, creating or retrieving those values if necessary. The returned map contains entries that were already cached, combined with newly loaded entries; it will never contain null keys or values.

Caches loaded by a CacheLoader will issue a single request to CacheLoader.loadAll(java.lang.Iterable<? extends K>) for all keys which are not already present in the cache. All entries returned by CacheLoader.loadAll(java.lang.Iterable<? extends K>) will be stored in the cache, over-writing any previously cached values. This method will throw an exception if CacheLoader.loadAll(java.lang.Iterable<? extends K>) returns null, returns a map containing null keys or values, or fails to return an entry for each requested key.

Note that duplicate elements in keys, as determined by Object.equals(java.lang.Object), will be ignored.

Throws:

ExecutionException - if a checked exception was thrown while loading the value. (ExecutionException is thrown even if computation was interrupted by an InterruptedException.)

UncheckedExecutionException - if an unchecked exception was thrown while loading the values

ExecutionError - if an error was thrown while loading the values

Since:

11.0

apply

@Deprecated
V apply(K key)

Deprecated. Provided to satisfy the Function interface; use get(K) or getUnchecked(K) instead.

Description copied from interface: Function

Returns the result of applying this function to input. This method is generally expected, but not absolutely required, to have the following properties:

• Its execution does not cause any observable side effects.
• The computation is consistent with equals; that is, Objects.equal(a, b) implies that Objects.equal(function.apply(a), function.apply(b)).

Specified by:

apply in interface Function<K,V>

Throws:

UncheckedExecutionException - if an exception was thrown while loading the value. (As described in the documentation for getUnchecked(K), LoadingCache should be used as a Function only with cache loaders that throw only unchecked exceptions.)

refresh

void refresh(K key)

Loads a new value for key key, possibly asynchronously. While the new value is loading the previous value (if any) will continue to be returned by get(key) unless it is evicted. If the new value is loaded successfully it will replace the previous value in the cache; if an exception is thrown while refreshing the previous value will remain, and the exception will be logged (using Logger) and swallowed.

Caches loaded by a CacheLoader will call CacheLoader.reload(K, V) if the cache currently contains a value for key, and CacheLoader.load(K) otherwise. Loading is asynchronous only if CacheLoader.reload(K, V) was overridden with an asynchronous implementation.

Returns without doing anything if another thread is currently loading the value for key. If the cache loader associated with this cache performs refresh asynchronously then this method may return before refresh completes.

Since:

11.0

asMap

ConcurrentMap<K,V> asMap()

Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to the map directly affect the cache.

Note that although the view is modifiable, no method on the returned map will ever cause entries to be automatically loaded.

Specified by:

asMap in interface Cache<K,V>