com.google.common.cache
Class AbstractCache<K,V>

java.lang.Object
  com.google.common.cache.AbstractCache<K,V>

All Implemented Interfaces:

Cache<K,V>

Direct Known Subclasses:

AbstractLoadingCache

@Beta
@GwtCompatible
public abstract class AbstractCache<K,V>
extends Object
implements Cache<K,V>

This class provides a skeletal implementation of the Cache interface to minimize the effort required to implement this interface.

To implement a cache, the programmer needs only to extend this class and provide an implementation for the put(K, V) and Cache.getIfPresent(java.lang.Object) methods. getAllPresent(java.lang.Iterable) is implemented in terms of Cache.getIfPresent(java.lang.Object); putAll(java.util.Map) is implemented in terms of put(K, V), invalidateAll(Iterable) is implemented in terms of invalidate(java.lang.Object). The method cleanUp() is a no-op. All other methods throw an UnsupportedOperationException.

Since:

10.0

Author:

Charles Fry

Nested Class Summary

static class	AbstractCache.SimpleStatsCounter A thread-safe AbstractCache.StatsCounter implementation for use by Cache implementors.
static interface	AbstractCache.StatsCounter Accumulates statistics during the operation of a Cache for presentation by Cache.stats().

Constructor Summary

protected

AbstractCache() Constructor for use by subclasses.

Method Summary

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, Callable<? extends V> valueLoader) Returns the value associated with key in this cache, obtaining that value from valueLoader if necessary.
ImmutableMap<K,V>	getAllPresent(Iterable<?> keys) This implementation of getAllPresent lacks any insight into the internal cache data structure, and is thus forced to return the query keys instead of the cached keys.
void	invalidate(Object key) Discards any cached value for key key.
void	invalidateAll() Discards all entries in the cache.
void	invalidateAll(Iterable<?> keys) Discards any cached values for keys keys.
void	put(K key, V value) Associates value with key 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.

Methods inherited from class java.lang.Object

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

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

getIfPresent

Constructor Detail

AbstractCache

protected AbstractCache()

Constructor for use by subclasses.

Method Detail

get

public V get(K key,
             Callable<? extends V> valueLoader)
      throws ExecutionException

Description copied from interface: Cache

Returns the value associated with key in this cache, obtaining that value from valueLoader if necessary. No observable state associated with this cache is modified until loading completes. This method provides a simple substitute for the conventional "if cached, return; otherwise create, cache and return" pattern.

Warning: as with CacheLoader.load(K), valueLoader must not return null; it may either return a non-null value or throw an exception.

Specified by:

get in interface Cache<K,V>

Throws:

ExecutionException - if a checked exception was thrown while loading the value

Since:

11.0

getAllPresent

public ImmutableMap<K,V> getAllPresent(Iterable<?> keys)

This implementation of getAllPresent lacks any insight into the internal cache data structure, and is thus forced to return the query keys instead of the cached keys. This is only possible with an unsafe cast which requires keys to actually be of type K. Returns a map of the values associated with keys in this cache. The returned map will only contain entries which are already present in the cache.

Specified by:

getAllPresent in interface Cache<K,V>

Since:

11.0

put

public void put(K key,
                V value)

Description copied from interface: Cache

Associates value with key in this cache. If the cache previously contained a value associated with key, the old value is replaced by value.

Prefer Cache.get(Object, Callable) when using the conventional "if cached, return; otherwise create, cache and return" pattern.

Specified by:

put in interface Cache<K,V>

Since:

11.0

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 calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress.

Specified by:

putAll in interface Cache<K,V>

Since:

12.0

cleanUp

public void cleanUp()

Description copied from interface: Cache

Performs any pending maintenance operations needed by the cache. Exactly which activities are performed -- if any -- is implementation-dependent.

Specified by:

cleanUp in interface Cache<K,V>

size

public long size()

Description copied from interface: Cache

Returns the approximate number of entries in this cache.

Specified by:

size in interface Cache<K,V>

invalidate

public void invalidate(Object key)

Description copied from interface: Cache

Discards any cached value for key key.

Specified by:

invalidate in interface Cache<K,V>

invalidateAll

public void invalidateAll(Iterable<?> keys)

Description copied from interface: Cache

Discards any cached values for keys keys.

Specified by:

invalidateAll in interface Cache<K,V>

Since:

11.0

invalidateAll

public void invalidateAll()

Description copied from interface: Cache

Discards all entries in the cache.

Specified by:

invalidateAll in interface Cache<K,V>

stats

public CacheStats stats()

Description copied from interface: Cache

Returns a current snapshot of this cache's cumulative statistics. All stats are initialized to zero, and are monotonically increasing over the lifetime of the cache.

Specified by:

stats in interface Cache<K,V>

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.

Specified by:

asMap in interface Cache<K,V>