org.rakeshv.utils
Class DynamicCache<K,V>

java.lang.Object
  org.rakeshv.utils.DynamicCache<K,V>

All Implemented Interfaces:

java.util.Map<K,V>

 class DynamicCache<K,V>
extends java.lang.Object
implements Map<K,V>

A Map used to implement a dynamic cache that grows only up to the heap space available to the process. The map values are stored as SoftReferences thus ensuring that the least recently used values will be garbage collected when heap space runs short.

This class uses a ConcurrentHashMap internally to manage the cache.

Mappings for garbage collected values from the Map will be removed when invoking the following methods:

1. put(K, V)
2. remove(java.lang.Object)
3. clear()

In addition to the above, the DynamicCache.Cleaner task will run at the interval specified for the org.rakeshv.utils.DynamicCache.cleanInterval system property (in seconds), or at 600 second intervals if no property is specified. This will ensure that memory is not wasted on holding mappings for garbage collected values, or for maintaing the values in the ReferenceQueue.

Copyright 2004-2006 Rakesh Vidyadharan

Version:

$Id: DynamicCache.java,v 1.9 2006/03/14 20:08:21 rakesh Exp $

Author:

Rakesh Vidyadharan 2004 October 1

Nested Class Summary

private static class	DynamicCache.Cleaner A TimerTask that is used to schedule clearing of mappings for garbage collected DynamicCache.Value objects.
class	DynamicCache.Entry<K,V> An implementation of the Map.Entry interface.
private class	DynamicCache.Value<V> A sub-class of SoftReference used to represent the value stored in the map.

Nested classes/interfaces inherited from interface org.rakeshv.utils.Map

Map.Statistics

Field Summary

(package private) static java.lang.String	CLEAN_INTERVAL_PROPERTY The name of the system property that defines the interval at which the DynamicCache.Cleaner will run.
private static java.lang.String	CLEAN_INTERVAL_VALUE The default value for the CLEAN_INTERVAL_PROPERTY in seconds.
private static DynamicCache.Cleaner	cleaner The DynamicCache.Cleaner that is used to remove garbage collected DynamicCache.Value instances from each instance of the cache.
(package private) static int	CONCURRENCY Default concurrency level for the map.
private static java.util.logging.Logger	logger The logger used to write information about cache activities.
private java.util.concurrent.ConcurrentHashMap<K,DynamicCache.Value<V>>	map The instance of ConcurrentHashMap that is used to hold the key-value entries.
private java.lang.ref.ReferenceQueue<V>	queue The reference que for the garbage collected values.
private LinkedHashMap.Statistics	statistics An instance of LinkedHashMap.Statistics that is used to track usage of the cache.

Constructor Summary

DynamicCache()
Default constructor.

DynamicCache(int capacity)
Constructs a new instance with the specified initial capacity.

DynamicCache(int capacity, float loadFactor)
Constructs a new instance with the specified initial capacity and load factor.

DynamicCache(int capacity, float loadFactor, int concurrency)
Constructs an empty DynamicCache instance with the specified initial capacity, load factor and ordering mode.

DynamicCache(java.util.Map<K,V> map)
Constructs an ordered DynamicCache instance with the same mappings as the specified map.

Method Summary

private int	clean() Clean out entries from the map whose value has been garbage collected.
void	clear() Removes all mappings from this map (optional operation).
boolean	containsKey(java.lang.Object key) Returns true if this map contains a mapping for the specified key.
boolean	containsValue(java.lang.Object value) Returns true if this map maps one or more keys to the specified value.
java.util.Set<java.util.Map.Entry<K,V>>	entrySet() Returns a set view of the mappings contained in this map.
boolean	equals(java.lang.Object o) Compares the specified object with this map for equality.
V	get(java.lang.Object key) Returns the value to which this map maps the specified key.
int	getMaxEntries() Returns the total number of entries in the cache.
Map.Statistics	getStatistics() Returns statistics.
int	hashCode() Returns the hash code value for this map.
boolean	isEmpty() Returns true if this map contains no key-value mappings.
java.util.Set<K>	keySet() Returns a set view of the keys contained in this map.
V	put(K key, V value) Associates the specified value with the specified key in this map.
void	putAll(java.util.Map<? extends K,? extends V> t) Copies all of the mappings from the specified map to this map The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map.
V	remove(java.lang.Object key) Removes the mapping for this key from this map if it is present.
void	setMaxEntries(int maxEntries) Set the maximum number of items that can be stored in the map.
int	size() Returns the number of key-value mappings in this map.
java.util.Collection<V>	values() Returns a collection view of the values contained in this map.

Methods inherited from class java.lang.Object

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

Field Detail

CONCURRENCY

static final int CONCURRENCY

Default concurrency level for the map.

See Also:

Constant Field Values

CLEAN_INTERVAL_PROPERTY

static final java.lang.String CLEAN_INTERVAL_PROPERTY

The name of the system property that defines the interval at which the DynamicCache.Cleaner will run.

See Also:

Constant Field Values

CLEAN_INTERVAL_VALUE

private static final java.lang.String CLEAN_INTERVAL_VALUE

The default value for the CLEAN_INTERVAL_PROPERTY in seconds. "600"

See Also:

Constant Field Values

logger

private static final java.util.logging.Logger logger

The logger used to write information about cache activities.

cleaner

private static final DynamicCache.Cleaner cleaner

The DynamicCache.Cleaner that is used to remove garbage collected DynamicCache.Value instances from each instance of the cache.

map

private final java.util.concurrent.ConcurrentHashMap<K,DynamicCache.Value<V>> map

The instance of ConcurrentHashMap that is used to hold the key-value entries.

queue

private final java.lang.ref.ReferenceQueue<V> queue

The reference que for the garbage collected values.

statistics

private LinkedHashMap.Statistics statistics

An instance of LinkedHashMap.Statistics that is used to track usage of the cache.

Constructor Detail

DynamicCache

DynamicCache()

Default constructor. Creates a new Map with using the super class constructor.

DynamicCache

DynamicCache(int capacity)

Constructs a new instance with the specified initial capacity.

Parameters:

capacity - The maximum size for this map.

DynamicCache

DynamicCache(int capacity,
             float loadFactor)

Constructs a new instance with the specified initial capacity and load factor.

Parameters:

capacity - The maximum size for this map.

loadFactor - The load-factor to use.

DynamicCache

DynamicCache(int capacity,
             float loadFactor,
             int concurrency)

Constructs an empty DynamicCache instance with the specified initial capacity, load factor and ordering mode.

Parameters:

capacity - The maximum size for this map.

loadFactor - The load-factor to use.

concurrency - The estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.

DynamicCache

DynamicCache(java.util.Map<K,V> map)

Constructs an ordered DynamicCache instance with the same mappings as the specified map. The maximum size of this map is set to the size of the specified map.

Parameters:

map - The map to use to create the new instance.

Throws:

java.lang.NullPointerException - If the specified map is null.

See Also:

putAll(java.util.Map)

Method Detail

getMaxEntries

public final int getMaxEntries()

Returns the total number of entries in the cache. Since this cache is not size limited, it does not keep track of any user specified maximum value.

Returns:

int The total capacity of the cache.

setMaxEntries

public final void setMaxEntries(int maxEntries)

Set the maximum number of items that can be stored in the map. This method does nothing since a dynamic cache does not support setting hard size limits.

Parameters:

maxEntries - The value to set.

getStatistics

public final Map.Statistics getStatistics()

Returns statistics. This may be used by client applications to monitor cache usage.

Returns:

Statistics The value/reference of/to statistics.

size

public final int size()

Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:

size in interface java.util.Map<K,V>

Returns:

the number of key-value mappings in this map.

isEmpty

public final boolean isEmpty()

Returns true if this map contains no key-value mappings.

Specified by:

isEmpty in interface java.util.Map<K,V>

Returns:

true if this map contains no key-value mappings.

containsKey

public final boolean containsKey(java.lang.Object key)

Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Specified by:

containsKey in interface java.util.Map<K,V>

Parameters:

key - Key whose presence in this map is to be tested.

Returns:

true If this map contains a mapping for the specified key.

Throws:

java.lang.ClassCastException - If the key is of an inappropriate type for this map (optional).

java.lang.NullPointerException - If the key is null and this map does not permit null keys (optional).

containsValue

public final boolean containsValue(java.lang.Object value)

Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.

Specified by:

containsValue in interface java.util.Map<K,V>

Parameters:

value - Value whose presence in this map is to be tested.

Returns:

true If this map maps one or more keys to the specified value.

Throws:

java.lang.ClassCastException - If the value is of an inappropriate type for this map (optional).

java.lang.NullPointerException - If the value is null and this map does not permit null values (optional).

java.lang.UnsupportedOperationException - This operation is not supported by this map implementation.

get

public final V get(java.lang.Object key)

Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

Specified by:

get in interface java.util.Map<K,V>

Parameters:

key - Key whose associated value is to be returned.

Returns:

The value to which this map maps the specified key, or null if the map contains no mapping for this key.

Throws:

java.lang.ClassCastException - If the key is of an inappropriate type for this map (optional).

java.lang.NullPointerException - If the key is null and this map does not permit null keys (optional).

See Also:

containsKey( Object )

put

public final V put(K key,
                   V value)

Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.))

Specified by:

put in interface java.util.Map<K,V>

Parameters:

key - Key with which the specified value is to be associated.

value - Value to be associated with the specified key.

Returns:

Previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.

Throws:

java.lang.UnsupportedOperationException - If the put operation is not supported by this map.

java.lang.ClassCastException - If the class of the specified key or value prevents it from being stored in this map.

java.lang.IllegalArgumentException - If some aspect of this key or value prevents it from being stored in this map.

java.lang.NullPointerException - If this map does not permit null keys or values, and the specified key or value is null.

See Also:

clean()

remove

public final V remove(java.lang.Object key)

Removes the mapping for this key from this map if it is present. More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

Specified by:

remove in interface java.util.Map<K,V>

Parameters:

key - Key whose mapping is to be removed from the map.

Returns:

Previous value associated with specified key, or null if there was no mapping for key.

Throws:

java.lang.ClassCastException - If the key is of an inappropriate type for this map (optional).

java.lang.NullPointerException - If the key is null and this map does not permit null keys (optional).

java.lang.UnsupportedOperationException - if the remove method is not supported by this map.

See Also:

clean()

putAll

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

Copies all of the mappings from the specified map to this map The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is unspecified if the specified map is modified while the operation is in progress.

Specified by:

putAll in interface java.util.Map<K,V>

Parameters:

t - Mappings to be stored in this map.

Throws:

java.lang.UnsupportedOperationException - If the putAll method is not supported by this map.

java.lang.ClassCastException - If the class of a key or value in the specified map prevents it from being stored in this map.

java.lang.IllegalArgumentException - Some aspect of a key or value in the specified map prevents it from being stored in this map.

java.lang.NullPointerException - If the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values.

See Also:

put(K, V)

clear

public void clear()

Removes all mappings from this map (optional operation).

Specified by:

clear in interface java.util.Map<K,V>

Throws:

java.lang.UnsupportedOperationException - Clear is not supported by this map.

keySet

public java.util.Set<K> keySet()

Returns a set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

Specified by:

keySet in interface java.util.Map<K,V>

Returns:

A set view of the keys contained in this map.

values

public java.util.Collection<V> values()

Returns a collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

values in interface java.util.Map<K,V>

Returns:

A collection view of the values contained in this map.

entrySet

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

Returns a set view of the mappings contained in this map. Each element in the returned set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

entrySet in interface java.util.Map<K,V>

Returns:

A set view of the mappings contained in this map.

equals

public boolean equals(java.lang.Object o)

Compares the specified object with this map for equality. Returns true if the given object is also a map and the two Maps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.entrySet().equals(t2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.

Specified by:

equals in interface java.util.Map<K,V>

Overrides:

equals in class java.lang.Object

Parameters:

o - Object to be compared for equality with this map.

Returns:

true If the specified object is equal to this map.

hashCode

public int hashCode()

Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hashCodes of each entry in the map's entrySet view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.

Specified by:

hashCode in interface java.util.Map<K,V>

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code value for this map.

See Also:

equals(java.lang.Object)

clean

private int clean()

Clean out entries from the map whose value has been garbage collected. The garbage collected values are available in the queue reference queue.

Returns:

int The number of entries that were removed from the map.