org.apache.jcs.utils.struct

Class LRUMap

java.lang.Object

org.apache.jcs.utils.struct.LRUMap

All Implemented Interfaces:

java.util.Map

Direct Known Subclasses:

LRUMapJCS

public class LRUMap
extends java.lang.Object
implements java.util.Map

This is a simple LRUMap. It implements most of the map methods. It is not recommended that you use any but put, get, remove, and clear.

Children can implement the processRemovedLRU method if they want to handle the removal of the lest recently used item.

This class was abstracted out of the LRU Memory cache. Put, remove, and get should be thread safe. It uses a hashtable and our own double linked list.

Locking is done on the instance.

Author:

aaron smuts

Nested Class Summary

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

java.util.Map.Entry<K,V>

Field Summary

Fields

Modifier and Type	Field and Description
protected java.util.Map	map Map where items are stored by key.

Constructor Summary

Constructors

Constructor and Description
LRUMap() This creates an unbounded version.
LRUMap(int maxObjects) This sets the size limit.

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() This removes all the items.
boolean	containsKey(java.lang.Object key) Returns true if the map contains an element for the supplied key.
boolean	containsValue(java.lang.Object value) This is an expensive operation that determines if the object supplied is mapped to any key.
void	dumpCacheEntries() Dump the cache entries from first to list for debugging.
void	dumpMap() Dump the cache map for debugging.
java.util.Set	entrySet() This returns a set of entries.
java.lang.Object	get(java.lang.Object key)
int	getChunkSize()
java.lang.Object	getQuiet(java.lang.Object key) This gets an element out of the map without adjusting it's posisiton in the LRU.
IStats	getStatistics()
boolean	isEmpty() Returns true if the map is empty.
java.util.Set	keySet()
protected void	processRemovedLRU(java.lang.Object key, java.lang.Object value) This is called when an item is removed from the LRU.
java.lang.Object	put(java.lang.Object key, java.lang.Object value)
void	putAll(java.util.Map source)
java.lang.Object	remove(java.lang.Object key)
void	setChunkSize(int chunkSize) The chunk size is the number of items to remove when the max is reached.
int	size() This simply returned the number of elements in the map.
java.util.Collection	values()
protected void	verifyCache() Checks to see if all the items that should be in the cache are.
protected void	verifyCache(java.lang.Object key) Logs an error is an element that should be in the cache is not.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Field Detail

map

protected java.util.Map map

Map where items are stored by key.

Constructor Detail

LRUMap

public LRUMap()

This creates an unbounded version. Setting the max objects will result in spooling on subsequent puts.

LRUMap

public LRUMap(int maxObjects)

This sets the size limit.

Parameters:

maxObjects -

Method Detail

size

public int size()

This simply returned the number of elements in the map.

Specified by:

size in interface java.util.Map

See Also:

Map.size()

clear

public void clear()

This removes all the items. It clears the map and the double linked list.

Specified by:

clear in interface java.util.Map

See Also:

Map.clear()

isEmpty

public boolean isEmpty()

Returns true if the map is empty.

Specified by:

isEmpty in interface java.util.Map

See Also:

Map.isEmpty()

containsKey

public boolean containsKey(java.lang.Object key)

Returns true if the map contains an element for the supplied key.

Specified by:

containsKey in interface java.util.Map

See Also:

Map.containsKey(java.lang.Object)

containsValue

public boolean containsValue(java.lang.Object value)

This is an expensive operation that determines if the object supplied is mapped to any key.

Specified by:

containsValue in interface java.util.Map

See Also:

Map.containsValue(java.lang.Object)

values

public java.util.Collection values()

Specified by:

values in interface java.util.Map

Returns:

map.values();

putAll

public void putAll(java.util.Map source)

Specified by:

putAll in interface java.util.Map

Parameters:

source -

get

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

Specified by:

get in interface java.util.Map

Parameters:

key -

Returns:

Object

getQuiet

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

This gets an element out of the map without adjusting it's posisiton in the LRU. In other words, this does not count as being used. If the element is the last item in the list, it will still be the last itme in the list.

Parameters:

key -

Returns:

Object

remove

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

Specified by:

remove in interface java.util.Map

Parameters:

key -

Returns:

Object removed

put

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

Specified by:

put in interface java.util.Map

Parameters:

key -

value -

Returns:

Object

dumpCacheEntries

public void dumpCacheEntries()

Dump the cache entries from first to list for debugging.

dumpMap

public void dumpMap()

Dump the cache map for debugging.

verifyCache

protected void verifyCache()

Checks to see if all the items that should be in the cache are. Checks consistency between List and map.

verifyCache

protected void verifyCache(java.lang.Object key)

Logs an error is an element that should be in the cache is not.

Parameters:

key -

processRemovedLRU

protected void processRemovedLRU(java.lang.Object key,
                     java.lang.Object value)

This is called when an item is removed from the LRU. We just log some information.

Children can implement this method for special behavior.

Parameters:

key -

value -

setChunkSize

public void setChunkSize(int chunkSize)

The chunk size is the number of items to remove when the max is reached. By default it is 1.

Parameters:

chunkSize - The chunkSize to set.

getChunkSize

public int getChunkSize()

Returns:

Returns the chunkSize.

getStatistics

public IStats getStatistics()

Returns:

IStats

entrySet

public java.util.Set entrySet()

This returns a set of entries. Our LRUMapEntry is used since the value stored in the underlying map is a node in the double linked list. We wouldn't want to return this to the client, so we construct a new entry with the payload of the node.

TODO we should return out own set wrapper, so we can avoid the extra object creation if it isn't necessary.

Specified by:

entrySet in interface java.util.Map

See Also:

Map.entrySet()

keySet

public java.util.Set keySet()

Specified by:

keySet in interface java.util.Map

Returns:

map.keySet();