Class AbstractCache<K,V>

java.lang.Object
com.google.common.cache.AbstractCache<K,V>
All Implemented Interfaces:
Cache<K,V>
Direct Known Subclasses:
AbstractLoadingCache
@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<? extends java.lang.Object>) 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.

Since:
10.0
Author:
Charles Fry

  • Constructor Details

    • AbstractCache

      protected AbstractCache()
      Constructor for use by subclasses.

  • Method Details

    • 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 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.

      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<? extends Object> keys)
      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.

      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.

      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<? extends Object> 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, 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 the CacheBuilder.recordStats() method was called. If statistics are not being recorded, a CacheStats instance with zero for all values is returned.

      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.

      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.

      Specified by:
      asMap in interface Cache<K,V>