Interface Cache<K,V>
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- Type Parameters:
K
- the type of the cache's keys, which are not permitted to be nullV
- the type of the cache's values, which are not permitted to be null
- All Known Subinterfaces:
LoadingCache<K,V>
- All Known Implementing Classes:
AbstractCache
,AbstractLoadingCache
,ForwardingCache
,ForwardingCache.SimpleForwardingCache
,ForwardingLoadingCache
,ForwardingLoadingCache.SimpleForwardingLoadingCache
@DoNotMock("Use CacheBuilder.newBuilder().build()") @GwtCompatible public interface Cache<K,V>
A semi-persistent mapping from keys to values. Cache entries are manually added usingget(Object, Callable)
orput(Object, Object)
, and are stored in the cache until either evicted or manually invalidated. The common way to build instances is usingCacheBuilder
.Implementations of this interface are expected to be thread-safe, and can be safely accessed by multiple concurrent threads.
- Since:
- 10.0
- Author:
- Charles Fry
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description java.util.concurrent.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.V
get(K key, java.util.concurrent.Callable<? extends V> loader)
Returns the value associated withkey
in this cache, obtaining that value fromloader
if necessary.ImmutableMap<K,V>
getAllPresent(java.lang.Iterable<? extends java.lang.Object> keys)
Returns a map of the values associated withkeys
in this cache.V
getIfPresent(java.lang.Object key)
Returns the value associated withkey
in this cache, ornull
if there is no cached value forkey
.void
invalidate(java.lang.Object key)
Discards any cached value for keykey
.void
invalidateAll()
Discards all entries in the cache.void
invalidateAll(java.lang.Iterable<? extends java.lang.Object> keys)
Discards any cached values for keyskeys
.void
put(K key, V value)
Associatesvalue
withkey
in this cache.void
putAll(java.util.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.
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Method Detail
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getIfPresent
@CheckForNull @CanIgnoreReturnValue V getIfPresent(@CompatibleWith("K") java.lang.Object key)
Returns the value associated withkey
in this cache, ornull
if there is no cached value forkey
.- Since:
- 11.0
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get
@CanIgnoreReturnValue V get(K key, java.util.concurrent.Callable<? extends V> loader) throws java.util.concurrent.ExecutionException
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.
- Throws:
java.util.concurrent.ExecutionException
- if a checked exception was thrown while loading the valueUncheckedExecutionException
- if an unchecked exception was thrown while loading the valueExecutionError
- if an error was thrown while loading the value- Since:
- 11.0
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getAllPresent
ImmutableMap<K,V> getAllPresent(java.lang.Iterable<? extends java.lang.Object> keys)
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.- Since:
- 11.0
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put
void put(K key, V value)
Associatesvalue
withkey
in this cache. If the cache previously contained a value associated withkey
, the old value is replaced byvalue
.Prefer
get(Object, Callable)
when using the conventional "if cached, return; otherwise create, cache and return" pattern.- Since:
- 11.0
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putAll
void putAll(java.util.Map<? extends K,? extends V> m)
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.- Since:
- 12.0
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invalidate
void invalidate(@CompatibleWith("K") java.lang.Object key)
Discards any cached value for keykey
.
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invalidateAll
void invalidateAll(java.lang.Iterable<? extends java.lang.Object> keys)
Discards any cached values for keyskeys
.- Since:
- 11.0
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invalidateAll
void invalidateAll()
Discards all entries in the cache.
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size
long size()
Returns the approximate number of entries in this cache.
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stats
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. 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
java.util.concurrent.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.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.
Warning to users of Java 8+: do not call any of the new default methods that have been newly added to
ConcurrentMap
! These are marked with "Since: 1.8" in theConcurrentMap
documentation. They will not function correctly and it is impossible for Guava to fix them until Guava is ready to require Java 8 for all users.
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cleanUp
void cleanUp()
Performs any pending maintenance operations needed by the cache. Exactly which activities are performed -- if any -- is implementation-dependent.
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