org.zkoss.util

Class CacheMap<K,V>

java.lang.Object

org.zkoss.util.CacheMap<K,V>

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>, Cache<K,V>

Direct Known Subclasses:

ResourceCache

public class CacheMap<K,V>
extends Object
implements Map<K,V>, Cache<K,V>, Serializable, Cloneable

The cache map. The key-to-value mappings hold in this map is temporary. They are removed when GC demanding memory and a criteria is met. The criteria is whether the mapping is old enough (called lifetime), or the upper bound is hit (called max-size).

The criteria can be changed by overriding canExpunge(int, org.zkoss.util.CacheMap.Value<V>). When to check the criteria can be changed by overriding shallExpunge().

If the criteria is totally independent of GC, you could override shallExpunge() to always return true (rather than when GC is activated).

It is different from WeakHashMap:

• The mapping might be removed even if the key is hold somewhere (i.e., strong reachable).
• The mapping might not be removed when GC demanding memory if the criteria doesn't meet.
• It is not serializable.

Like other maps, it is not thread-safe. To get one, use java.util.Collections.synchronizedMap.

Implementation Note: there is another version of CacheMap that uses WeakReference for each value (refer to obsolete). The drawback is that all mapping will be queued and need to be examined, because GC tends to release all reference at once.

We don't use PhantomReference because it is still required to re-create the reference after enqueued.

Author:

tomyeh

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	CacheMap.Value<V> The class to hold key/value.

Field Summary

Fields

Modifier and Type	Field and Description
protected static int	EXPUNGE_CONTINUE Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote the searching of the next mapping shall continue.
protected static int	EXPUNGE_NO Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote it shall not be expunged.
protected static int	EXPUNGE_STOP Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote the searching of the next mapping shall stop.
protected static int	EXPUNGE_YES Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote it shall be expunged.

Fields inherited from interface org.zkoss.util.Cache

DEFAULT_LIFETIME, DEFAULT_MAX_SIZE

Constructor Summary

Constructors

Constructor and Description
CacheMap() Constructs a cache map.
CacheMap(boolean accessOrder) Constructs a cache map.
CacheMap(int cap) Constructs a cache map.
CacheMap(int cap, float load) Constructs a cache map.
CacheMap(int cap, float load, boolean accessOrder) Constructs a cache map.
CacheMap(int maxSize, int lifetime) Constructs a cache map with the specified max size and lifetime.
CacheMap(int maxSize, int lifetime, boolean accessOrder) Constructs a cache map with the specified max size and lifetime.

Method Summary

Modifier and Type	Method and Description
protected int	canExpunge(int size, CacheMap.Value<V> v) Tests whether certain value is OK to expunge.
void	clear() Clears all objects being cached.
Object	clone()
boolean	containsKey(Object key) Returns whether the specified key is stored.
boolean	containsKeyWithoutExpunge(Object key) Tests if the given key exists without trying to expunge for more memory.
boolean	containsValue(Object value)
Set<Map.Entry<K,V>>	entrySet()
boolean	equals(Object o)
int	expunge() Enforces to expunge items that exceeds the maximal allowed number or lifetime.
V	get(Object key) Returns the object of the specified key, or null if not found.
int	getLifetime() Gets the minimal lifetime, unit=milliseconds.
int	getMaxSize() Gets the maximal allowed size.
V	getWithoutExpunge(Object key) Returns the value without trying to expunge for more memory.
int	hashCode()
boolean	isEmpty()
boolean	isEmptyWithoutExpunge() Returns whether it is empty without trying to expunge first.
Set<K>	keySet()
protected void	onExpunge(CacheMap.Value<V> v) Called when a pair of key and value having been expunged.
V	put(K key, V value) Stores an object to the cache.
void	putAll(Map<? extends K,? extends V> map)
V	remove(Object key) Removes an object from the cache.
void	setLifetime(int lifetime) Sets the minimal lifetime.
void	setMaxSize(int maxsize) Sets the maximal allowed size.
protected boolean	shallExpunge() Returns whether it is time to expunge.
int	size()
int	sizeWithoutExpunge() Returns the size without trying to expunge first.
String	toString()
Collection<V>	values()

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

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

Field Detail

EXPUNGE_NO

protected static final int EXPUNGE_NO

Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote it shall not be expunged.

See Also:

Constant Field Values

EXPUNGE_YES

protected static final int EXPUNGE_YES

Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote it shall be expunged.

See Also:

Constant Field Values

EXPUNGE_CONTINUE

protected static final int EXPUNGE_CONTINUE

Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote the searching of the next mapping shall continue.

See Also:

Constant Field Values

EXPUNGE_STOP

protected static final int EXPUNGE_STOP

Returns by canExpunge(int, org.zkoss.util.CacheMap.Value<V>) to denote the searching of the next mapping shall stop.

See Also:

Constant Field Values

Constructor Detail

CacheMap

public CacheMap(int maxSize,
                int lifetime)

Constructs a cache map with the specified max size and lifetime. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().

Since:

3.0.0

CacheMap

public CacheMap()

Constructs a cache map. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().

CacheMap

public CacheMap(int cap)

Constructs a cache map. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().

CacheMap

public CacheMap(int cap,
                float load)

Constructs a cache map. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().

CacheMap

public CacheMap(boolean accessOrder)

Constructs a cache map.

Parameters:

accessOrder - whether to use the access order. Specify false for the insertion order.

Since:

6.0.0

CacheMap

public CacheMap(int maxSize,
                int lifetime,
                boolean accessOrder)

Constructs a cache map with the specified max size and lifetime.

Parameters:

accessOrder - whether to use the access order. Specify false for the insertion order.

Since:

6.0.0

CacheMap

public CacheMap(int cap,
                float load,
                boolean accessOrder)

Constructs a cache map.

Parameters:

accessOrder - whether to use the access order. Specify false for the insertion order.

Since:

6.0.0

Method Detail

onExpunge

protected void onExpunge(CacheMap.Value<V> v)

Called when a pair of key and value having been expunged. This method is called after it is removed, so you could add it back.

Default: does nothing

shallExpunge

protected boolean shallExpunge()

Returns whether it is time to expunge. Once shallExpunge returns true, values are examined one-by-one thru canExpunge(int, org.zkoss.util.CacheMap.Value<V>), and expunged if EXPUNGE_YES.

This implementation returns true only if GC was activated. You might override it to return true, such that expunge is enforced no matter GC was activated.

See Also:

canExpunge(int, org.zkoss.util.CacheMap.Value<V>)

canExpunge

protected int canExpunge(int size,
                         CacheMap.Value<V> v)

Tests whether certain value is OK to expunge.

Note: values are tested thru canExpunge(int, org.zkoss.util.CacheMap.Value<V>) only if shallExpunge() returns true.

Deriving classes might override this method to return different value for different criteria.

The return value could be a combination of EXPUNGE_xxx. One of EXPUNGE_YES and EXPUNGE_NO is returned to denote whether to expunge the mapping. One of EXPUNGE_CONTINUE and EXPUNGE_STOP is returned to denote whether to continue the searching of the next mapping for expunging.

Normally, you return either (EXPUNGE_YES|EXPUNGE_CONTINUE) or (EXPUNG_NO|EXPUNGE_STOP). Notice that the mapping is queried in the last-access order. Thus, you rarely needs to return (EXPUNGE_NO|EXPUNGE_CONTINUE) unless the appropriate one might be out of this order.

This implementation compares the access time and size. It returns (EXPUNGE_YES|EXPUNGE_CONTINUE) if OK, and (EXPUNGE_NO|EXPUNGE_STOP) if not.

Parameters:

size - the current size. It is used instead of size(), since the entry might not be removed yet (such as FastReadCache).

Returns:

a combination of EXPUNGE_xxx

See Also:

shallExpunge()

expunge

public int expunge()

Enforces to expunge items that exceeds the maximal allowed number or lifetime.

By default, this method is called only GC takes places.

Returns:

number of items left (size()) after expunged

Since:

3.6.1

getLifetime

public int getLifetime()

Gets the minimal lifetime, unit=milliseconds. An mapping won't be removed by GC unless the minimal lifetime or the maximal allowed size exceeds.

Specified by:

getLifetime in interface Cache<K,V>

See Also:

getMaxSize()

setLifetime

public void setLifetime(int lifetime)

Sets the minimal lifetime. Default: Cache.DEFAULT_LIFETIME.

Specified by:

setLifetime in interface Cache<K,V>

Parameters:

lifetime - the lifetime, unit=milliseconds; if non-positive, they will be removed immediately.

See Also:

getLifetime()

getMaxSize

public int getMaxSize()

Gets the maximal allowed size. Default: Cache.DEFAULT_MAX_SIZE. An mapping won't be removed by GC unless the minimal lifetime or the maximal allowed size exceeds.

Notice: getMaxSize() is only a soft limit. It takes effect only if GC takes place.

Specified by:

getMaxSize in interface Cache<K,V>

See Also:

getLifetime()

setMaxSize

public void setMaxSize(int maxsize)

Sets the maximal allowed size.

Specified by:

setMaxSize in interface Cache<K,V>

See Also:

getMaxSize()

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Map<K,V>

isEmptyWithoutExpunge

public boolean isEmptyWithoutExpunge()

Returns whether it is empty without trying to expunge first.

Since:

3.0.1

size

public int size()

Specified by:

size in interface Map<K,V>

sizeWithoutExpunge

public int sizeWithoutExpunge()

Returns the size without trying to expunge first.

Since:

3.0.1

clear

public void clear()

Description copied from interface: Cache

Clears all objects being cached.

Specified by:

clear in interface Map<K,V>

Specified by:

clear in interface Cache<K,V>

remove

public V remove(Object key)

Description copied from interface: Cache

Removes an object from the cache.

Specified by:

remove in interface Map<K,V>

Specified by:

remove in interface Cache<K,V>

Returns:

the object if found.

get

public V get(Object key)

Description copied from interface: Cache

Returns the object of the specified key, or null if not found.

Specified by:

get in interface Map<K,V>

Specified by:

get in interface Cache<K,V>

getWithoutExpunge

public V getWithoutExpunge(Object key)

Returns the value without trying to expunge for more memory. It is useful if you want to preserve all entries.

containsKey

public boolean containsKey(Object key)

Description copied from interface: Cache

Returns whether the specified key is stored.

Specified by:

containsKey in interface Map<K,V>

Specified by:

containsKey in interface Cache<K,V>

containsKeyWithoutExpunge

public boolean containsKeyWithoutExpunge(Object key)

Tests if the given key exists without trying to expunge for more memory.

containsValue

public boolean containsValue(Object value)

Specified by:

containsValue in interface Map<K,V>

put

public V put(K key,
             V value)

Description copied from interface: Cache

Stores an object to the cache.

Specified by:

put in interface Map<K,V>

Specified by:

put in interface Cache<K,V>

Returns:

the previous value of the same, or null if no such value

putAll

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

Specified by:

putAll in interface Map<K,V>

entrySet

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

Specified by:

entrySet in interface Map<K,V>

keySet

public Set<K> keySet()

Specified by:

keySet in interface Map<K,V>

values

public Collection<V> values()

Specified by:

values in interface Map<K,V>

hashCode

public int hashCode()

Specified by:

hashCode in interface Map<K,V>

Overrides:

hashCode in class Object

equals

public boolean equals(Object o)

Specified by:

equals in interface Map<K,V>

Overrides:

equals in class Object

toString

public String toString()

Overrides:

toString in class Object

clone

public Object clone()

Overrides:

clone in class Object