org.ceryle.util
Class Cache

java.lang.Object
  java.util.Dictionary<K,V>
      java.util.Hashtable
          org.ceryle.util.Cache

All Implemented Interfaces:

Serializable, Cloneable, Map

public class Cache
extends Hashtable

Extends Hashtable as an Object cache.

To Do

Provide a cache size limit using total storage size and delete cache objects past that threshold. Currently this is done on count only.

Version:

$Id: Cache.java,v 3.1 2007-06-15 12:09:55 altheim Exp $

Author:

Murray Altheim

See Also:

Serialized Form

Field Summary

static int	DEFAULT_SIZE The value of the default cache size.
static int	hysteresis The value of size-trimming hysteresis (the amount over the limit permitted prior to trimming, used to reduce the cost of trimming).

Constructor Summary

Cache()
Constructor for an Cache using the default cache size (of 50) and automatically checking the limit.

Cache(int limit, boolean autocheck)
Constructor for an Cache with a cache size limit and the boolean controlling whether the limit check is automatic or manual.

Method Summary

protected void	addToCache(String key, Object o) Adds the Object o to the cache using the String key as the key.
Object	checkCacheFor(String key) Checks the cache for an Object corresponding to key, returning null if it is not in the cache, or if caching is inactive.
void	checkLimit() Checks the current cache size against the limit and removes objects as necessary to reach the limit.
void	clear() Clears the document cache.
Object	get(Object key) Throws an exception.
Iterator	getAll() Returns an Iterator over the Objects in the cache.
Object	put(Object key, Object value) Throws an exception.
void	putAll(Map map) Throws an exception.
Object	remove(Object key) Throws an exception.
boolean	removeFromCache(Object o) Removes the Object o from the document cache, returning true if it was removed.
boolean	removeFromCache(String key) Removes the document specified by the String key from the cache, returning true if it was removed.
Collection	values() Throws an exception.

Methods inherited from class java.util.Hashtable

clone, contains, containsKey, containsValue, elements, entrySet, equals, hashCode, isEmpty, keys, keySet, rehash, size, toString

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_SIZE

public static final int DEFAULT_SIZE

The value of the default cache size. Value is 50.

See Also:

Constant Field Values

hysteresis

public static int hysteresis

The value of size-trimming hysteresis (the amount over the limit permitted prior to trimming, used to reduce the cost of trimming). Default value is 10.

Constructor Detail

Cache

public Cache()

Constructor for an Cache using the default cache size (of 50) and automatically checking the limit.

Cache

public Cache(int limit,
             boolean autocheck)

Constructor for an Cache with a cache size limit and the boolean controlling whether the limit check is automatic or manual. The minimum acceptable value for limit is 10.

Method Detail

addToCache

protected void addToCache(String key,
                          Object o)

Adds the Object o to the cache using the String key as the key. Note: If the key is already in use, this replaces the existing cache entry with the new Object. If caching is inactive or either parameter is null this method does nothing (rather than throw an exception).

checkCacheFor

public Object checkCacheFor(String key)

Checks the cache for an Object corresponding to key, returning null if it is not in the cache, or if caching is inactive.

removeFromCache

public boolean removeFromCache(String key)

Removes the document specified by the String key from the cache, returning true if it was removed.

removeFromCache

public boolean removeFromCache(Object o)

Removes the Object o from the document cache, returning true if it was removed. This is somewhat expensive as we need to iterate through the entire Map.Entry set to locate the key so it can be removed from the keyset and queue.

getAll

public Iterator getAll()

Returns an Iterator over the Objects in the cache.

clear

public void clear()

Clears the document cache.

Specified by:

clear in interface Map

Overrides:

clear in class Hashtable

checkLimit

public void checkLimit()

Checks the current cache size against the limit and removes objects as necessary to reach the limit. To provide some hysteresis, the size is permitted to exceed the limit by the value of hysteresis prior to trimming.

values

public final Collection values()

Throws an exception. Use getAll() instead.

Specified by:

values in interface Map

Overrides:

values in class Hashtable

remove

public final Object remove(Object key)

Throws an exception. Use removeFromCache(String) instead.

Specified by:

remove in interface Map

Overrides:

remove in class Hashtable

get

public final Object get(Object key)

Throws an exception. Use checkCacheFor(String) instead.

Specified by:

get in interface Map

Overrides:

get in class Hashtable

put

public final Object put(Object key,
                        Object value)

Throws an exception. Use addToCache(String,Object) instead.

Specified by:

put in interface Map

Overrides:

put in class Hashtable

putAll

public final void putAll(Map map)

Throws an exception. Use addToCache(String,Object) instead.

Specified by:

putAll in interface Map

Overrides:

putAll in class Hashtable