com.fasterxml.jackson.databind.util

Class LRUMap<K,V>

  • All Implemented Interfaces:
    LookupCache<K,V>, Serializable

    public class LRUMap<K,V>
extends Object
implements LookupCache<K,V>, Serializable
    Helper for simple bounded maps used for reusing lookup values.

    Note that serialization behavior is such that contents are NOT serialized, on assumption that all use cases are for caching where persistence does not make sense. The only thing serialized is the cache size of Map.

    NOTE: since version 2.4.2, this is NOT an LRU-based at all; reason being that it is not possible to use JDK components that do LRU _AND_ perform well wrt synchronization on multi-core systems. So we choose efficient synchronization over potentially more efficient handling of entries.

    And yes, there are efficient LRU implementations such as concurrentlinkedhashmap; but at this point we really try to keep external deps to minimum. Plan from Jackson 2.12 is to focus more on pluggability as LookupCache and let users, frameworks, provide their own cache implementations.

    See Also:
    Serialized Form

    • Field Detail

      • _maxEntries

        protected final transient int _maxEntries

      • _jdkSerializeMaxEntries

        protected transient int _jdkSerializeMaxEntries
        Ugly hack, to work through the requirement that _value is indeed final, and that JDK serialization won't call ctor(s) if Serializable is implemented.
        Since:
        2.1

    • Constructor Detail

      • LRUMap

        public LRUMap(int initialEntries,
              int maxEntries)

    • Method Detail

      • get

        public V get(Object key)
        Description copied from interface: LookupCache
        NOTE: key is of type Object only to retain binary backwards-compatibility
        Specified by:
        get in interface LookupCache<K,V>
        Returns:
        value associated with key (can return null)

      • clear

        public void clear()
        Description copied from interface: LookupCache
        Method for removing all contents this cache has.
        Specified by:
        clear in interface LookupCache<K,V>

      • size

        public int size()
        Specified by:
        size in interface LookupCache<K,V>
        Returns:
        Number of entries currently in cache: may be approximate, only to be used for diagnostics, metrics reporting

      • readResolve

        protected Object readResolve()

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