Class ForwardingCache<K,V>
- java.lang.Object
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- com.google.common.collect.ForwardingObject
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- com.google.common.cache.ForwardingCache<K,V>
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- All Implemented Interfaces:
Cache<K,V>
- Direct Known Subclasses:
ForwardingCache.SimpleForwardingCache
,ForwardingLoadingCache
@GwtIncompatible public abstract class ForwardingCache<K,V> extends ForwardingObject implements Cache<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.- Since:
- 10.0
- Author:
- Charles Fry
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
ForwardingCache.SimpleForwardingCache<K,V>
A simplified version ofForwardingCache
where subclasses can pass in an already constructedCache
as the delegate.
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Constructor Summary
Constructors Modifier Constructor Description protected
ForwardingCache()
Constructor for use by subclasses.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description ConcurrentMap<K,V>
asMap()
Returns a view of the entries stored in this cache as a thread-safe map.void
cleanUp()
Performs any pending maintenance operations needed by the cache.protected abstract Cache<K,V>
delegate()
Returns the backing delegate instance that methods are forwarded to.V
get(K key, Callable<? extends V> valueLoader)
Returns the value associated withkey
in this cache, obtaining that value fromloader
if necessary.ImmutableMap<K,V>
getAllPresent(Iterable<? extends Object> keys)
Returns a map of the values associated withkeys
in this cache.@Nullable V
getIfPresent(Object key)
Returns the value associated withkey
in this cache, ornull
if there is no cached value forkey
.void
invalidate(Object key)
Discards any cached value for keykey
.void
invalidateAll()
Discards all entries in the cache.void
invalidateAll(Iterable<? extends Object> keys)
Discards any cached values for keyskeys
.void
put(K key, V value)
Associatesvalue
withkey
in this cache.void
putAll(Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to the cache.long
size()
Returns the approximate number of entries in this cache.CacheStats
stats()
Returns a current snapshot of this cache's cumulative statistics, or a set of default values if the cache is not recording statistics.-
Methods inherited from class com.google.common.collect.ForwardingObject
toString
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Constructor Detail
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ForwardingCache
protected ForwardingCache()
Constructor for use by subclasses.
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Method Detail
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delegate
protected abstract Cache<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 asForwardingSet.delegate()
. Concrete subclasses override this method to supply the instance being decorated.- Specified by:
delegate
in classForwardingObject
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getIfPresent
public @Nullable V getIfPresent(Object key)
Description copied from interface:Cache
Returns the value associated withkey
in this cache, ornull
if there is no cached value forkey
.- Specified by:
getIfPresent
in interfaceCache<K,V>
- Since:
- 11.0
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get
public V get(K key, Callable<? extends V> valueLoader) throws ExecutionException
Description copied from interface:Cache
Returns the value associated withkey
in this cache, obtaining that value fromloader
if necessary. The method improves upon the conventional "if cached, return; otherwise create, cache and return" pattern. For further improvements, useLoadingCache
and itsget(K)
method instead of this one.Among the improvements that this method and
LoadingCache.get(K)
both provide are:- awaiting the result of a pending load rather than starting a redundant one
- eliminating the error-prone caching boilerplate
- tracking load statistics
Among the further improvements that
LoadingCache
can provide but this method cannot:- consolidation of the loader logic to a single authoritative location
- refreshing of entries, including automated refreshing
- bulk loading requests, including bulk loading implementations
Warning: For any given key, every
loader
used with it should compute the same value. Otherwise, a call that passes oneloader
may return the result of another call with a differently behavingloader
. For example, a call that requests a short timeout for an RPC may wait for a similar call that requests a long timeout, or a call by an unprivileged user may return a resource accessible only to a privileged user making a similar call. To prevent this problem, create a key object that includes all values that affect the result of the query. Or useLoadingCache.get(K)
, which lacks the ability to refer to state other than that in the key.Warning: as with
CacheLoader.load(K)
,loader
must not returnnull
; it may either return a non-null value or throw an exception.No observable state associated with this cache is modified until loading completes.
- Specified by:
get
in interfaceCache<K,V>
- Throws:
ExecutionException
- if a checked exception was thrown while loading the value- Since:
- 11.0
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getAllPresent
public ImmutableMap<K,V> getAllPresent(Iterable<? extends Object> keys)
Description copied from interface:Cache
Returns a map of the values associated withkeys
in this cache. The returned map will only contain entries which are already present in the cache.- Specified by:
getAllPresent
in interfaceCache<K,V>
- Since:
- 11.0
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put
public void put(K key, V value)
Description copied from interface:Cache
Associatesvalue
withkey
in this cache. If the cache previously contained a value associated withkey
, the old value is replaced byvalue
.Prefer
Cache.get(Object, Callable)
when using the conventional "if cached, return; otherwise create, cache and return" pattern.
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putAll
public void putAll(Map<? extends K,? extends V> m)
Description copied from interface:Cache
Copies all of the mappings from the specified map to the cache. The effect of this call is equivalent to that of callingput(k, v)
on this map once for each mapping from keyk
to valuev
in the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress.
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invalidate
public void invalidate(Object key)
Description copied from interface:Cache
Discards any cached value for keykey
.- Specified by:
invalidate
in interfaceCache<K,V>
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invalidateAll
public void invalidateAll(Iterable<? extends Object> keys)
Description copied from interface:Cache
Discards any cached values for keyskeys
.- Specified by:
invalidateAll
in interfaceCache<K,V>
- Since:
- 11.0
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invalidateAll
public void invalidateAll()
Description copied from interface:Cache
Discards all entries in the cache.- Specified by:
invalidateAll
in interfaceCache<K,V>
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size
public long size()
Description copied from interface:Cache
Returns the approximate number of entries in this cache.
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stats
public CacheStats stats()
Description copied from interface:Cache
Returns a current snapshot of this cache's cumulative statistics, or a set of default values if the cache is not recording statistics. All statistics begin at zero and never decrease over the lifetime of the cache.Warning: this cache may not be recording statistical data. For example, a cache created using
CacheBuilder
only does so if theCacheBuilder.recordStats()
method was called. If statistics are not being recorded, aCacheStats
instance with zero for all values is returned.
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asMap
public ConcurrentMap<K,V> asMap()
Description copied from interface:Cache
Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to the map directly affect the cache.Iterators from the returned map are at least weakly consistent: they are safe for concurrent use, but if the cache is modified (including by eviction) after the iterator is created, it is undefined which of the changes (if any) will be reflected in that iterator.
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