Interface Cache<K,V>

Type Parameters:
K - the type of keys maintained by this cache
V - the type of mapped values
All Known Subinterfaces:
LoadingCache<K,V>, LocalLoadingCache<C,K,V>, LocalManualCache<C,K,V>
All Known Implementing Classes:
BoundedLocalCache.BoundedLocalLoadingCache, BoundedLocalCache.BoundedLocalManualCache, LocalAsyncLoadingCache.LoadingCacheView, UnboundedLocalCache.UnboundedLocalLoadingCache, UnboundedLocalCache.UnboundedLocalManualCache

@ThreadSafe public interface Cache<K,V>
A semi-persistent mapping from keys to values. Cache entries are manually added using get(Object, Function) or put(Object, Object), and are stored in the cache until either evicted or manually invalidated.

Implementations of this interface are expected to be thread-safe, and can be safely accessed by multiple concurrent threads.

  • Method Summary

    Modifier and Type
    Method
    Description
    Returns a view of the entries stored in this cache as a thread-safe map.
    void
    Performs any pending maintenance operations needed by the cache.
    long
    Returns the approximate number of entries in this cache.
    get(K key, Function<? super K,? extends V> mappingFunction)
    Returns the value associated with the key in this cache, obtaining that value from the mappingFunction if necessary.
    Returns a map of the values associated with the keys in this cache.
    Returns the value associated with the key in this cache, or null if there is no cached value for the key.
    void
    Discards any cached value for the key.
    void
    Discards all entries in the cache.
    void
    Discards any cached values for the keys.
    Returns access to inspect and perform low-level operations on this cache based on its runtime characteristics.
    void
    put(K key, V value)
    Associates the value with the key in this cache.
    void
    putAll(Map<? extends K,? extends V> map)
    Copies all of the mappings from the specified map to the cache.
    Returns a current snapshot of this cache's cumulative statistics.
  • Method Details

    • getIfPresent

      @CheckForNull V getIfPresent(@Nonnull Object key)
      Returns the value associated with the key in this cache, or null if there is no cached value for the key.
      Parameters:
      key - the key whose associated value is to be returned
      Returns:
      the value to which the specified key is mapped, or null if this map contains no mapping for the key
      Throws:
      NullPointerException - if the specified key is null
    • get

      @CheckForNull V get(@Nonnull K key, @Nonnull Function<? super K,? extends V> mappingFunction)
      Returns the value associated with the key in this cache, obtaining that value from the mappingFunction if necessary. This method provides a simple substitute for the conventional "if cached, return; otherwise create, cache and return" pattern.

      If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this cache unless null. The entire method invocation is performed atomically, so the function is applied at most once per key. Some attempted update operations on this cache by other threads may be blocked while the computation is in progress, so the computation should be short and simple, and must not attempt to update any other mappings of this cache.

      Warning: as with CacheLoader.load(K), mappingFunction must not attempt to update any other mappings of this cache.

      Parameters:
      key - the key with which the specified value is to be associated
      mappingFunction - the function to compute a value
      Returns:
      the current (existing or computed) value associated with the specified key, or null if the computed value is null
      Throws:
      NullPointerException - if the specified key or mappingFunction is null
      IllegalStateException - if the computation detectably attempts a recursive update to this cache that would otherwise never complete
      RuntimeException - or Error if the mappingFunction does so, in which case the mapping is left unestablished
    • getAllPresent

      @Nonnull Map<K,V> getAllPresent(@Nonnull Iterable<?> keys)
      Returns a map of the values associated with the keys in this cache. The returned map will only contain entries which are already present in the cache.
      Parameters:
      keys - the keys whose associated values are to be returned
      Returns:
      the unmodifiable mapping of keys to values for the specified keys found in this cache
      Throws:
      NullPointerException - if the specified collection is null or contains a null element
    • put

      void put(@Nonnull K key, @Nonnull V value)
      Associates the value with the key in this cache. If the cache previously contained a value associated with the key, the old value is replaced by the new value.

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

      Parameters:
      key - the key with which the specified value is to be associated
      value - value to be associated with the specified key
      Throws:
      NullPointerException - if the specified key or value is null
    • putAll

      void putAll(@Nonnull Map<? extends K,? extends V> map)
      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.
      Parameters:
      map - the mappings to be stored in this cache
      Throws:
      NullPointerException - if the specified map is null or the specified map contains null keys or values
    • invalidate

      void invalidate(@Nonnull Object key)
      Discards any cached value for the key. The behavior of this operation is undefined for an entry that is being loaded and is otherwise not present.
      Parameters:
      key - the key whose mapping is to be removed from the cache
      Throws:
      NullPointerException - if the specified key is null
    • invalidateAll

      void invalidateAll(@Nonnull Iterable<?> keys)
      Discards any cached values for the keys. The behavior of this operation is undefined for an entry that is being loaded and is otherwise not present.
      Parameters:
      keys - the keys whose associated values are to be removed
      Throws:
      NullPointerException - if the specified collection is null or contains a null element
    • invalidateAll

      void invalidateAll()
      Discards all entries in the cache. The behavior of this operation is undefined for an entry that is being loaded and is otherwise not present.
    • estimatedSize

      @Nonnegative long estimatedSize()
      Returns the approximate number of entries in this cache. The value returned is an estimate; the actual count may differ if there are concurrent insertions or removals, or if some entries are pending removal due to expiration or weak/soft reference collection. In the case of stale entries this inaccuracy can be mitigated by performing a cleanUp() first.
      Returns:
      the estimated number of mappings
    • stats

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

      Due to the performance penalty of maintaining statistics, some implementations may not record the usage history immediately or at all.

      Returns:
      the current snapshot of the statistics of this cache
    • asMap

      @Nonnull 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.

      Returns:
      a thread-safe view of this cache supporting all of the optional Map operations
    • cleanUp

      void cleanUp()
      Performs any pending maintenance operations needed by the cache. Exactly which activities are performed -- if any -- is implementation-dependent.
    • policy

      @Nonnull Policy<K,V> policy()
      Returns access to inspect and perform low-level operations on this cache based on its runtime characteristics. These operations are optional and dependent on how the cache was constructed and what abilities the implementation exposes.
      Returns:
      access to inspect and perform advanced operations based on the cache's characteristics