org.jasig.portal.concurrency.caching
Class LRUCache

java.lang.Object
  java.util.AbstractMap
      java.util.HashMap
          org.jasig.portal.concurrency.caching.LRUCache

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.util.Map

public class LRUCache
extends java.util.HashMap

A rewrite of SmartCache that uses a moderate LRU algorithm: entries are purged from the cache via periodic sweeps rather than in response to specific cache additions. Note that sweeps have to be kicked off externally, e.g.,

int MAX_CACHE_SIZE = 1000;
int MAX_UNUSED_TIME_MILLIS = 30*60*1000;
LRUCache cache = new LRUCache(MAX_CACHE_SIZE, MAX_UNUSED_TIME_MILLIS);
// ... put stuff in ...
cache.sweepCache()
// ... put more stuff in ...


At the end of the sweep, the cache will have no more (and possibly less) than maxSize entries, though the sweep may have to reduce maxUnusedTimeMillis in order to get there.

Version:

$Revision: 1.7 $

Author:

Ken Weiner, Dan Ellentuck

See Also:

SmartCache, Serialized Form

Nested Class Summary

private class

LRUCache.ValueWrapper

Field Summary

protected static int	DEFAULT_MAX_SIZE
protected static int	DEFAULT_MAX_UNUSED_TIME_MILLIS
protected int	maxSize
protected int	maxUnusedTimeMillis

Constructor Summary

LRUCache()

LRUCache(int size)

LRUCache(int size, int maxUnusedAge)

Method Summary

void	clear() Synchronizes removal of ALL entries from the cache.
java.lang.Object	get(java.lang.Object key) Get the object from the cache and reset the timestamp.
private java.lang.Object[]	getKeySetArray()
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Add a new value to the cache.
java.lang.Object	remove(java.lang.Object key) Synchronizes removal of an entry from the cache.
void	sweepCache() Sweep the cache until it gets back under maxSize.

Methods inherited from class java.util.HashMap

clone, containsKey, containsValue, entrySet, isEmpty, keySet, putAll, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Field Detail

DEFAULT_MAX_SIZE

protected static int DEFAULT_MAX_SIZE

maxSize

protected int maxSize

DEFAULT_MAX_UNUSED_TIME_MILLIS

protected static int DEFAULT_MAX_UNUSED_TIME_MILLIS

maxUnusedTimeMillis

protected int maxUnusedTimeMillis

Constructor Detail

LRUCache

public LRUCache()

LRUCache

public LRUCache(int size)

LRUCache

public LRUCache(int size,
                int maxUnusedAge)

Parameters:

size - int

maxUnusedAge - int

Method Detail

clear

public void clear()

Synchronizes removal of ALL entries from the cache.

Specified by:

clear in interface java.util.Map

Overrides:

clear in class java.util.HashMap

get

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

Get the object from the cache and reset the timestamp.

Specified by:

get in interface java.util.Map

Overrides:

get in class java.util.HashMap

Parameters:

key - the key, typically a String

Returns:

the value to which the key is mapped in this cache; null if the key is not mapped to any value in this cache.

put

public java.lang.Object put(java.lang.Object key,
                            java.lang.Object value)

Add a new value to the cache.

Specified by:

put in interface java.util.Map

Overrides:

put in class java.util.HashMap

Parameters:

key - the key, typically a String

value - the value

Returns:

the previous value of the specified key in this hashtable, or null if it did not have one.

remove

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

Synchronizes removal of an entry from the cache.

Specified by:

remove in interface java.util.Map

Overrides:

remove in class java.util.HashMap

Parameters:

key - the key, typically a String

Returns:

the previous value of the specified key in this hashtable, or null if it did not have one.

sweepCache

public void sweepCache()

Sweep the cache until it gets back under maxSize.

getKeySetArray

private java.lang.Object[] getKeySetArray()