org.jivesoftware.util.cache

Interface Cache<K extends Serializable,V extends Serializable>

All Superinterfaces:

Map<K,V>

All Known Implementing Classes:

CacheWrapper, CaffeineCache, ComponentCacheWrapper, DefaultCache

public interface Cache<K extends Serializable,V extends Serializable>
extends Map<K,V>

General purpose cache. It stores objects associated with unique keys in memory for fast access. All keys and values added to the cache must implement the Serializable interface. Values may implement the Cacheable interface, which allows the cache to determine object size much more quickly. These restrictions allow a cache to never grow larger than a specified number of bytes and to optionally be distributed over a cluster of servers.

If the cache does grow too large, objects will be removed such that those that are accessed least frequently are removed first. Because expiration happens automatically, the cache makes no guarantee as to how long an object will remain in cache after it is put in.

Optionally, a maximum lifetime for all objects can be specified. In that case, objects will be deleted from cache after that amount of time, even if they are frequently accessed. This feature is useful if objects put in cache represent data that should be periodically refreshed; for example, information from a database.

All cache operations are thread safe.

Note that neither keys or values can be null; A NullPointerException will be thrown attempting to place or retrieve null values in to the cache.

See Also:

Cacheable

Nested Class Summary

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

Map.Entry<K,V>

Method Summary

Modifier and Type	Method and Description
Set<Map.Entry<K,V>>	entrySet() IMPORTANT: Unlike the standard Map.entrySet() implementation, the set returned from this method cannot be modified.
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.
default Lock	getLock(K key) Returns an existing Lock on the specified key or creates a new one if none was found.
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 the cache.
Set<K>	keySet() IMPORTANT: Unlike the standard Map.keySet() implementation, the set returned from this method cannot be modified.
void	setMaxCacheSize(int maxSize) Sets the maximum size of the cache in bytes.
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 the cache
Collection<V>	values() IMPORTANT: Unlike the standard Map.values() implementation, the collection returned from this method cannot be modified.

Methods inherited from interface java.util.Map

clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, equals, forEach, get, getOrDefault, hashCode, isEmpty, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size

Method Detail

getName

String getName()

Returns the name of the cache.

Returns:

the name of the cache.

setName

void setName(String name)

Sets the name of the cache

Parameters:

name - the name of the cache

getMaxCacheSize

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.

Returns:

the maximum size of the cache in bytes.

setMaxCacheSize

void setMaxCacheSize(int maxSize)

Sets 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.

Note: If using the Hazelcast clustering plugin, this will not take effect until the next time the cache is created

Parameters:

maxSize - the maximum size of the cache in bytes.

getMaxLifetime

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.

Returns:

the maximum number of milliseconds before objects are expired.

setMaxLifetime

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.

Note: If using the Hazelcast clustering plugin, this will not take effect until the next time the cache is created

Parameters:

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

getCacheSize

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.

Returns:

the size of the cache contents in bytes.

getCacheHits

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.

Returns:

the number of cache hits.

getCacheMisses

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.

Returns:

the number of cache hits.

values

Collection<V> values()

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>

Returns:

an unmodifiable collection view of the values contained in this map

entrySet

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

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>

Returns:

an unmodifiable set view of the mappings contained in this map

keySet

Set<K> keySet()

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>

Returns:

an unmodifiable set view of the keys contained in this map

getLock

default Lock getLock(K key)

Returns an existing Lock on the specified key or creates a new one if none was found. This operation is thread safe. Successive calls with the same key may or may not return the same Lock. However, different threads asking for the same Lock at the same time will get the same Lock object.

The supplied cache may or may not be used depending whether the server is running on cluster mode or not. When not running as part of a cluster then the lock will be unrelated to the cache and will only be visible in this JVM.

Parameters:

key - the object that defines the visibility or scope of the lock.

Returns:

an existing lock on the specified key or creates a new one if none was found.