- All Implemented Interfaces:
- Direct Known Subclasses:
@GwtCompatible public abstract class AbstractCache<K,V> extends Object implements Cache<K,V>This class provides a skeletal implementation of the
Cacheinterface 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
getAllPresent(java.lang.Iterable<?>)is implemented in terms of
putAll(java.util.Map<? extends K, ? extends V>)is implemented in terms of
invalidateAll(Iterable)is implemented in terms of
invalidate(java.lang.Object). The method
cleanUp()is a no-op. All other methods throw an
- Charles Fry
Constructors Modifier Constructor Description
AbstractCache()Constructor for use by subclasses.
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
asMap()Returns a view of the entries stored in this cache as a thread-safe map.
cleanUp()Performs any pending maintenance operations needed by the cache.
get(K key, Callable<? extends V> valueLoader)Returns the value associated with
keyin this cache, obtaining that value from
getAllPresent(Iterable<?> keys)Returns a map of the values associated with
keysin this cache.
invalidate(Object key)Discards any cached value for key
invalidateAll()Discards all entries in the cache.
invalidateAll(Iterable<?> keys)Discards any cached values for keys
put(K key, V value)Associates
keyin this cache.
putAll(Map<? extends K,? extends V> m)Copies all of the mappings from the specified map to the cache.
size()Returns the approximate number of entries in this cache.
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 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
protected AbstractCache()Constructor for use by subclasses.
getReturns the value associated with
keyin this cache, obtaining that value from
loaderif necessary. The method improves upon the conventional "if cached, return; otherwise create, cache and return" pattern. For further improvements, use
get(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
LoadingCachecan 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
loaderused with it should compute the same value. Otherwise, a call that passes one
loadermay return the result of another call with a differently behaving
loader. 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 use
LoadingCache.get(K), which lacks the ability to refer to state other than that in the key.
Warning: as with
loadermust not return
null; it may either return a non-null value or throw an exception.
No observable state associated with this cache is modified until loading completes.
public ImmutableMap<K,V> getAllPresent(Iterable<?> keys)Returns a map of the values associated with
keysin this cache. The returned map will only contain entries which are already present in the cache.
This implementation of
getAllPresentlacks 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
keysto actually be of type
keyin this cache. If the cache previously contained a value associated with
key, the old value is replaced by
Cache.get(Object, Callable)when using the conventional "if cached, return; otherwise create, cache and return" pattern.
putAllCopies 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
vin the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress.
public void cleanUp()Performs any pending maintenance operations needed by the cache. Exactly which activities are performed -- if any -- is implementation-dependent.
public long size()Returns the approximate number of entries in this cache.
public void invalidate(Object key)Discards any cached value for key
public void invalidateAll(Iterable<?> keys)Discards any cached values for keys
public void invalidateAll()Discards all entries in the cache.
public 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
CacheBuilderonly does so if the
CacheBuilder.recordStats()method was called. If statistics are not being recorded, a
CacheStatsinstance with zero for all values is returned.
public 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.