com.fasterxml.jackson.databind.util

Class LRUMap<K,V>

java.lang.Object

com.fasterxml.jackson.databind.util.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 Summary

Fields

Modifier and Type	Field and Description
protected 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.
protected ConcurrentHashMap<K,V>	_map
protected int	_maxEntries

Constructor Summary

Constructors

Constructor and Description
LRUMap(int initialEntries, int maxEntries)

Method Summary

Modifier and Type	Method and Description
void	clear() Method for removing all contents this cache has.
V	get(Object key) NOTE: key is of type Object only to retain binary backwards-compatibility
V	put(K key, V value)
V	putIfAbsent(K key, V value)
protected Object	readResolve()
int	size()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

_maxEntries

protected final transient int _maxEntries

_map

protected final transient ConcurrentHashMap<K,V> _map

_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

put

public V put(K key,
             V value)

Specified by:

put in interface LookupCache<K,V>

putIfAbsent

public V putIfAbsent(K key,
                     V value)

Specified by:

putIfAbsent in interface LookupCache<K,V>

Since:

2.5

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()