Package com.google.common.cache

Class ForwardingLoadingCache<K,V>

java.lang.Object

com.google.common.collect.ForwardingObject

com.google.common.cache.ForwardingCache<K,V>

com.google.common.cache.ForwardingLoadingCache<K,V>

All Implemented Interfaces:

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

Direct Known Subclasses:

ForwardingLoadingCache.SimpleForwardingLoadingCache

@GwtIncompatible
public abstract class ForwardingLoadingCache<K,V>
extends ForwardingCache<K,V>
implements LoadingCache<K,V>

A cache which forwards all its method calls to another cache. Subclasses should override one or more methods to modify the behavior of the backing cache as desired per the decorator pattern.

Note that get(K), getUnchecked(K), and apply(K) all expose the same underlying functionality, so should probably be overridden as a group.

Since:

11.0

Author:

Charles Fry

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ForwardingLoadingCache.SimpleForwardingLoadingCache<K,V>	A simplified version of ForwardingLoadingCache where subclasses can pass in an already constructed LoadingCache as the delegate.

Nested classes/interfaces inherited from class com.google.common.cache.ForwardingCache

ForwardingCache.SimpleForwardingCache<K,V>

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	ForwardingLoadingCache()	Constructor for use by subclasses.

Method Summary

Modifier and Type	Method	Description
V	apply(K key)	Returns the result of applying this function to input.
protected abstract LoadingCache<K,V>	delegate()	Returns the backing delegate instance that methods are forwarded to.
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, possibly asynchronously.

Methods inherited from class com.google.common.cache.ForwardingCache

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

Methods inherited from class com.google.common.collect.ForwardingObject

toString

Methods inherited from class java.lang.Object

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

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

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

asMap

Constructor Detail

ForwardingLoadingCache

protected ForwardingLoadingCache()

Constructor for use by subclasses.

Method Detail

delegate

protected abstract LoadingCache<K,V> delegate()

Description copied from class: ForwardingObject

Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.

Specified by:

delegate in class ForwardingCache<K,V>

get

public V get(K key)
      throws ExecutionException

Description copied from interface: LoadingCache

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 LoadingCache.get(K) or LoadingCache.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 LoadingCache.getUnchecked(K) over this method.

Specified by:

get in interface LoadingCache<K,V>

Throws:

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

getUnchecked

public V getUnchecked(K key)

Description copied from interface: LoadingCache

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 LoadingCache.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 LoadingCache.get(K) or LoadingCache.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 LoadingCache.get(K) instead.

Specified by:

getUnchecked in interface LoadingCache<K,V>

getAll

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

Description copied from interface: LoadingCache

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.

Specified by:

getAll in interface LoadingCache<K,V>

Throws:

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

apply

public V apply(K key)

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>

Specified by:

apply in interface LoadingCache<K,V>

refresh

public void refresh(K key)

Description copied from interface: LoadingCache

Loads a new value for 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.

Specified by:

refresh in interface LoadingCache<K,V>