@GwtCompatible public abstract class AbstractCache<K,V> extends Object implements Cache<K,V>
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<? extends K, ? extends V>) 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.
| Modifier and Type | Class and Description |
|---|---|
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(). |
| Modifier | Constructor and Description |
|---|---|
protected |
AbstractCache()
Constructor for use by subclasses.
|
| Modifier and Type | Method and 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.
|
V |
get(K key,
Callable<? extends V> valueLoader)
Returns the value associated with
key in this cache, obtaining that value from loader if necessary. |
ImmutableMap<K,V> |
getAllPresent(Iterable<?> keys)
Returns a map of the values associated with
keys in this cache. |
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, or a set of default values if
the cache is not recording statistics.
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitgetIfPresentprotected AbstractCache()
public V get(K key, Callable<? extends V> valueLoader) throws ExecutionException
Cachekey in this cache, obtaining that value from loader if necessary. The method improves upon the conventional "if cached, return; otherwise
create, cache and return" pattern. For further improvements, use LoadingCache and its
get(K) method instead of this one.
Among the improvements that this method and LoadingCache.get(K) both provide are:
Among the further improvements that LoadingCache can provide but this method cannot:
Warning: For any given key, every loader used with it should compute the same
value. Otherwise, a call that passes one loader may 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 CacheLoader.load(K), loader must 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.
get in interface Cache<K,V>ExecutionException - if a checked exception was thrown while loading the valuepublic ImmutableMap<K,V> getAllPresent(Iterable<?> keys)
keys in this cache. The returned map will
only contain entries which are already present in the cache.
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.
getAllPresent in interface Cache<K,V>public void put(K key, V value)
Cachevalue 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.
public void putAll(Map<? extends K,? extends V> m)
Cacheput(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.public void cleanUp()
Cachepublic long size()
Cachepublic void invalidate(Object key)
Cachekey.invalidate in interface Cache<K,V>public void invalidateAll(Iterable<?> keys)
Cachekeys.invalidateAll in interface Cache<K,V>public void invalidateAll()
CacheinvalidateAll in interface Cache<K,V>public CacheStats stats()
CacheWarning: this cache may not be recording statistical data. For example, a cache
created using CacheBuilder only does so if the CacheBuilder.recordStats() method
was called. If statistics are not being recorded, a CacheStats instance with zero for
all values is returned.
public ConcurrentMap<K,V> asMap()
CacheIterators 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 the
ConcurrentMap 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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