org.jivesoftware.util.cache

Class DefaultCache<K extends Serializable,V extends Serializable>

java.lang.Object

org.jivesoftware.util.cache.DefaultCache<K,V>

All Implemented Interfaces:

Map<K,V>, Cache<K,V>

public class DefaultCache<K extends Serializable,V extends Serializable>
extends Object
implements Cache<K,V>

Default, non-distributed implementation of the Cache interface. The algorithm for cache is as follows: a HashMap is maintained for fast object lookup. Two linked lists are maintained: one keeps objects in the order they are accessed from cache, the other keeps objects in the order they were originally added to cache. When objects are added to cache, they are first wrapped by a CacheObject which maintains the following pieces of information:

• The size of the object (in bytes).
• A pointer to the node in the linked list that maintains accessed order for the object. Keeping a reference to the node lets us avoid linear scans of the linked list.
• A pointer to the node in the linked list that maintains the age of the object in cache. Keeping a reference to the node lets us avoid linear scans of the linked list.

To get an object from cache, a hash lookup is performed to get a reference to the CacheObject that wraps the real object we are looking for. The object is subsequently moved to the front of the accessed linked list and any necessary cache cleanups are performed. Cache deletion and expiration is performed as needed.

Author:

Matt Tucker

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Field Summary

Fields

Modifier and Type	Field and Description
protected Map<K,org.jivesoftware.util.cache.DefaultCache.CacheObject<V>>	map The map the keys and values are stored in.

Method Summary

Modifier and Type	Method and Description
void	clear()
boolean	containsKey(Object key)
boolean	containsValue(Object value)
Set<Map.Entry<K,V>>	entrySet() IMPORTANT: Unlike the standard Map.entrySet() implementation, the set returned from this method cannot be modified.
V	get(Object key)
long	getCacheCulls(Duration duration)
long	getCacheHits() Returns the number of cache hits.
long	getCacheMisses() Returns the number of cache misses.
int	getCacheSize() Returns the size of the cache contents in bytes.
long	getMaxCacheSize() Returns the maximum size of the cache (in bytes).
long	getMaxLifetime() Returns the maximum number of milliseconds that any object can live in cache.
String	getName() Returns the name of this cache.
boolean	isEmpty()
Set<K>	keySet() IMPORTANT: Unlike the standard Map.keySet() implementation, the set returned from this method cannot be modified.
V	put(K key, V value)
void	putAll(Map<? extends K,? extends V> map)
V	remove(Object key)
void	setMaxCacheSize(int maxCacheSize) Sets the maximum size of the cache.
void	setMaxLifetime(long maxLifetime) Sets the maximum number of milliseconds that any object can live in cache.
void	setName(String name) Sets the name of this cache.
int	size()
Collection<V>	values() IMPORTANT: Unlike the standard Map.values() implementation, the collection returned from this method cannot be modified.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.jivesoftware.util.cache.Cache

getLock

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, equals, forEach, getOrDefault, hashCode, merge, putIfAbsent, remove, replace, replace, replaceAll

Field Detail

map

protected Map<K extends Serializable,org.jivesoftware.util.cache.DefaultCache.CacheObject<V extends Serializable>> map

The map the keys and values are stored in.

Method Detail

put

public V put(K key,
             V value)

Specified by:

put in interface Map<K extends Serializable,V extends Serializable>

get

public V get(Object key)

Specified by:

get in interface Map<K extends Serializable,V extends Serializable>

remove

public V remove(Object key)

Specified by:

remove in interface Map<K extends Serializable,V extends Serializable>

clear

public void clear()

Specified by:

clear in interface Map<K extends Serializable,V extends Serializable>

size

public int size()

Specified by:

size in interface Map<K extends Serializable,V extends Serializable>

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Map<K extends Serializable,V extends Serializable>

values

public Collection<V> values()

Description copied from interface: Cache

IMPORTANT: Unlike the standard Map.values() implementation, the collection returned from this method cannot be modified.

Specified by:

values in interface Map<K extends Serializable,V extends Serializable>

Specified by:

values in interface Cache<K extends Serializable,V extends Serializable>

Returns:

an unmodifiable collection view of the values contained in this map

containsKey

public boolean containsKey(Object key)

Specified by:

containsKey in interface Map<K extends Serializable,V extends Serializable>

putAll

public void putAll(Map<? extends K,? extends V> map)

Specified by:

putAll in interface Map<K extends Serializable,V extends Serializable>

containsValue

public boolean containsValue(Object value)

Specified by:

containsValue in interface Map<K extends Serializable,V extends Serializable>

entrySet

public Set<Map.Entry<K,V>> entrySet()

Description copied from interface: Cache

IMPORTANT: Unlike the standard Map.entrySet() implementation, the set returned from this method cannot be modified.

Specified by:

entrySet in interface Map<K extends Serializable,V extends Serializable>

Specified by:

entrySet in interface Cache<K extends Serializable,V extends Serializable>

Returns:

an unmodifiable set view of the mappings contained in this map

keySet

public Set<K> keySet()

Description copied from interface: Cache

IMPORTANT: Unlike the standard Map.keySet() implementation, the set returned from this method cannot be modified.

Specified by:

keySet in interface Map<K extends Serializable,V extends Serializable>

Specified by:

keySet in interface Cache<K extends Serializable,V extends Serializable>

Returns:

an unmodifiable set view of the keys contained in this map

getName

public String getName()

Returns the name of this cache. The name is completely arbitrary and used only for display to administrators.

Specified by:

getName in interface Cache<K extends Serializable,V extends Serializable>

Returns:

the name of this cache.

setName

public void setName(String name)

Sets the name of this cache.

Specified by:

setName in interface Cache<K extends Serializable,V extends Serializable>

Parameters:

name - the name of this cache.

getCacheHits

public long getCacheHits()

Returns the number of cache hits. A cache hit occurs every time the get method is called and the cache contains the requested object.

Keeping track of cache hits and misses lets one measure how efficient the cache is; the higher the percentage of hits, the more efficient.

Specified by:

getCacheHits in interface Cache<K extends Serializable,V extends Serializable>

Returns:

the number of cache hits.

getCacheMisses

public long getCacheMisses()

Returns the number of cache misses. A cache miss occurs every time the get method is called and the cache does not contain the requested object.

Keeping track of cache hits and misses lets one measure how efficient the cache is; the higher the percentage of hits, the more efficient.

Specified by:

getCacheMisses in interface Cache<K extends Serializable,V extends Serializable>

Returns:

the number of cache hits.

getCacheSize

public int getCacheSize()

Returns the size of the cache contents in bytes. This value is only a rough approximation, so cache users should expect that actual VM memory used by the cache could be significantly higher than the value reported by this method.

Specified by:

getCacheSize in interface Cache<K extends Serializable,V extends Serializable>

Returns:

the size of the cache contents in bytes.

getMaxCacheSize

public long getMaxCacheSize()

Returns the maximum size of the cache (in bytes). If the cache grows larger than the max size, the least frequently used items will be removed. If the max cache size is set to -1, there is no size limit.

Specified by:

getMaxCacheSize in interface Cache<K extends Serializable,V extends Serializable>

Returns:

the maximum size of the cache (-1 indicates unlimited max size).

setMaxCacheSize

public void setMaxCacheSize(int maxCacheSize)

Sets the maximum size of the cache. If the cache grows larger than the max size, the least frequently used items will be removed. If the max cache size is set to -1, there is no size limit.

Specified by:

setMaxCacheSize in interface Cache<K extends Serializable,V extends Serializable>

Parameters:

maxCacheSize - the maximum size of this cache (-1 indicates unlimited max size).

getMaxLifetime

public long getMaxLifetime()

Returns the maximum number of milliseconds that any object can live in cache. Once the specified number of milliseconds passes, the object will be automatically expired from cache. If the max lifetime is set to -1, then objects never expire.

Specified by:

getMaxLifetime in interface Cache<K extends Serializable,V extends Serializable>

Returns:

the maximum number of milliseconds before objects are expired.

setMaxLifetime

public void setMaxLifetime(long maxLifetime)

Sets the maximum number of milliseconds that any object can live in cache. Once the specified number of milliseconds passes, the object will be automatically expired from cache. If the max lifetime is set to -1, then objects never expire.

Specified by:

setMaxLifetime in interface Cache<K extends Serializable,V extends Serializable>

Parameters:

maxLifetime - the maximum number of milliseconds before objects are expired.

getCacheCulls

public long getCacheCulls(Duration duration)