org.mmbase.cache
Class Cache<K,V>

java.lang.Object
  org.mmbase.cache.Cache<K,V>

All Implemented Interfaces:

Map<K,V>, CacheMBean, SizeMeasurable

Direct Known Subclasses:

AbstractImages.CKeyCache, AttributeCache, BlobCache, Caches.OperationsCache, FactoryCache, NodeCache, QueryResultCache, RelationsCache, ResultCache, TemplateCache, URLCache

public abstract class Cache<K,V>
extends Object
implements SizeMeasurable, Map<K,V>, CacheMBean

A base class for all Caches. Extend this class for other caches.

Version:

$Id: Cache.java 41989 2010-04-20 16:45:39Z michiel $

Author:

Michiel Meeuwissen

Nested Class Summary

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

Map.Entry<K,V>

Field Summary

protected Object	lock
protected int	maxEntrySize

Constructor Summary

Cache(int size)

Method Summary

protected boolean	checkCachePolicy(Object key) Checks whether the key object should be cached.
void	clear()
boolean	contains(Object key)
boolean	containsKey(Object key)
boolean	containsValue(Object value)
Set<Map.Entry<K,V>>	entrySet()
boolean	equals(Object o)
V	get(Object key) Like 'get' of Maps but considers if the cache is active or not, and the cache policy of the key.
double	getAvarageValueLength() Returns the average 'length' of the values in the cache.
int	getByteSize() Determines the byte-size of this object
int	getByteSize(SizeOf sizeof) Determines the byte-size of this object using the given SizeOf instance.
int	getCheapByteSize() Returns the sum of bytesizes of every key and value.
int	getCount(K key)
protected int	getDefaultMaxEntrySize() This has to be overridden by Caches which support max entry size.
String	getDescription() Gives a description for this cache type.
long	getHits() Returns the number of times an element was succesfully retrieved from the table.
Class<?>	getImplementation()
Object	getLock() If you want to structurally modify this cache, synchronize on this object.
int	getMaxEntrySize() Return the maximum entry size for the cache in bytes.
int	getMaxSize()
long	getMisses() Returns the number of times an element cpould not be retrieved from the table.
String	getName() Returns a name for this cache type.
long	getPuts() Returns the number of times an element was committed to the table.
double	getRatio() Returns the ratio of hits and misses.
int	getSize()
String	getStats() Returns statistics on this table.
int	hashCode()
boolean	isActive() Wether this cache is active or not.
boolean	isEmpty()
Set<K>	keySet()
int	maxSize()
V	put(K key, V value) Like 'put' of LRUHashtable but considers if the cache is active or not.
void	putAll(Map<? extends K,? extends V> t)
Cache<K,V>	putCache() Puts this cache in the caches repository.
V	remove(Object key)
void	reset() Reset 'puts', 'misses' and 'puts' to 0.
void	setActive(boolean a) Sets this cache to active or passive.
(package private) void	setImplementation(String clazz, Map<String,String> configValues)
void	setMaxEntrySize(int i)
void	setMaxSize(int size)
int	size()
String	toString()
Collection<V>	values()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

maxEntrySize

protected int maxEntrySize

lock

protected volatile Object lock

Constructor Detail

Cache

public Cache(int size)

Method Detail

setImplementation

void setImplementation(String clazz,
                       Map<String,String> configValues)

getLock

public final Object getLock()

If you want to structurally modify this cache, synchronize on this object.

Since:

MMBase-1.8.6

getName

public String getName()

Returns a name for this cache type. Default it is the class name, but this normally will be overriden.

Specified by:

getName in interface CacheMBean

getDescription

public String getDescription()

Gives a description for this cache type. This can be used in cache overviews.

Specified by:

getDescription in interface CacheMBean

getMaxEntrySize

public int getMaxEntrySize()

Return the maximum entry size for the cache in bytes. If the cache-type supports it (default no), then no values bigger then this will be stored in the cache.

Specified by:

getMaxEntrySize in interface CacheMBean

See Also:

getMaxEntrySize()

setMaxEntrySize

public void setMaxEntrySize(int i)

Specified by:

setMaxEntrySize in interface CacheMBean

Since:

MMBase-1.9.2

See Also:

setMaxEntrySize(int)

getAvarageValueLength

public double getAvarageValueLength()

Returns the average 'length' of the values in the cache. Whatever that may mean. For a QueryResultCache the length obviously is the length of the cached lists. May return NaN if unknown or undetermined.

Specified by:

getAvarageValueLength in interface CacheMBean

Since:

MMBase-1.9.2

getDefaultMaxEntrySize

protected int getDefaultMaxEntrySize()

This has to be overridden by Caches which support max entry size.

entrySet

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

Specified by:

entrySet in interface Map<K,V>

getImplementation

public Class<?> getImplementation()

Since:

MMBase-1.8.6

checkCachePolicy

protected boolean checkCachePolicy(Object key)

Checks whether the key object should be cached. This method returns false if either the current cache is inactive, or the object to cache has a cache policy associated that prohibits caching of the object.

Parameters:

key - the object to be cached

Returns:

true if the object can be cached

Since:

MMBase-1.8

get

public V get(Object key)

Like 'get' of Maps but considers if the cache is active or not, and the cache policy of the key.

Specified by:

get in interface Map<K,V>

put

public V put(K key,
             V value)

Like 'put' of LRUHashtable but considers if the cache is active or not.

Specified by:

put in interface Map<K,V>

getHits

public long getHits()

Returns the number of times an element was succesfully retrieved from the table.

Specified by:

getHits in interface CacheMBean

See Also:

getHits()

getMisses

public long getMisses()

Returns the number of times an element cpould not be retrieved from the table.

Specified by:

getMisses in interface CacheMBean

See Also:

getMisses()

getPuts

public long getPuts()

Returns the number of times an element was committed to the table.

Specified by:

getPuts in interface CacheMBean

See Also:

getPuts()

reset

public void reset()

Reset 'puts', 'misses' and 'puts' to 0.

Specified by:

reset in interface CacheMBean

Since:

MMBase-1.9.2

See Also:

reset()

setMaxSize

public void setMaxSize(int size)

Specified by:

setMaxSize in interface CacheMBean

maxSize

public int maxSize()

getMaxSize

public int getMaxSize()

Specified by:

getMaxSize in interface CacheMBean

See Also:

getMaxSize()

size

public int size()

Specified by:

size in interface Map<K,V>

See Also:

Map.size()

getSize

public int getSize()

Specified by:

getSize in interface CacheMBean

See Also:

getSize()

contains

public boolean contains(Object key)

getCount

public int getCount(K key)

getRatio

public double getRatio()

Returns the ratio of hits and misses. The higher the ratio, the more succesfull the table retrieval is. A value of 1 means every attempt to retrieve data is succesfull, while a value nearing 0 means most times the object requested it is not available. Generally a high ratio means the table can be shrunk, while a low ratio means its size needs to be increased.

Specified by:

getRatio in interface CacheMBean

Returns:

A double between 0 and 1 or NaN.

See Also:

getRatio()

getStats

public String getStats()

Returns statistics on this table. The information shown includes number of accesses, ratio of misses and hits, current size, and number of puts.

setActive

public void setActive(boolean a)

Sets this cache to active or passive. TODO: Writing back to caches.xml if necessary (if this call was nog caused by change of caches.xml itself)

Specified by:

setActive in interface CacheMBean

See Also:

isActive()

toString

public String toString()

Overrides:

toString in class Object

isActive

public final boolean isActive()

Wether this cache is active or not.

Specified by:

isActive in interface CacheMBean

getByteSize

public int getByteSize()

Description copied from interface: SizeMeasurable

Determines the byte-size of this object

Specified by:

getByteSize in interface CacheMBean

Specified by:

getByteSize in interface SizeMeasurable

getByteSize

public int getByteSize(SizeOf sizeof)

Description copied from interface: SizeMeasurable

Determines the byte-size of this object using the given SizeOf instance. A SizeOf instance stores a Set already counted objects. So this method is typically called by SizeOf itself (recursion).

Specified by:

getByteSize in interface SizeMeasurable

getCheapByteSize

public int getCheapByteSize()

Returns the sum of bytesizes of every key and value. This may count too much, because objects (like Nodes) may occur in more then one value, but this is considerably cheaper then getByteSize(), which has to keep a Collection of every counted object.

Since:

MMBase-1.8

clear

public void clear()

Specified by:

clear in interface Map<K,V>

Specified by:

clear in interface CacheMBean

See Also:

Map.clear()

containsKey

public boolean containsKey(Object key)

Specified by:

containsKey in interface Map<K,V>

See Also:

Map.containsKey(java.lang.Object)

containsValue

public boolean containsValue(Object value)

Specified by:

containsValue in interface Map<K,V>

See Also:

Map.containsValue(java.lang.Object)

equals

public boolean equals(Object o)

Specified by:

equals in interface Map<K,V>

Overrides:

equals in class Object

See Also:

Map.equals(java.lang.Object)

hashCode

public int hashCode()

Specified by:

hashCode in interface Map<K,V>

Overrides:

hashCode in class Object

See Also:

Map.hashCode()

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Map<K,V>

See Also:

Map.isEmpty()

keySet

public Set<K> keySet()

Specified by:

keySet in interface Map<K,V>

See Also:

Map.keySet()

putAll

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

Specified by:

putAll in interface Map<K,V>

See Also:

Map.putAll(java.util.Map)

remove

public V remove(Object key)

Specified by:

remove in interface Map<K,V>

See Also:

Map.remove(java.lang.Object)

values

public Collection<V> values()

Specified by:

values in interface Map<K,V>

See Also:

Map.values()

putCache

public Cache<K,V> putCache()

Puts this cache in the caches repository.

See Also:

CacheManager.putCache(Cache)