lazyj.cache

Class GenericLastValuesCache<K,V>

java.lang.Object

lazyj.cache.GenericLastValuesCache<K,V>

Type Parameters:

K - key type

V - value type

All Implemented Interfaces:

java.io.Serializable, CacheElement<K,V>

public abstract class GenericLastValuesCache<K,V>
extends java.lang.Object
implements CacheElement<K,V>, java.io.Serializable

Keep a cache of the last used values. The user has to implement a way to resolve missing keys.

Since:

2007-03-08

Author:

costing

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GenericLastValuesCache()

Method Summary

Methods

Modifier and Type	Method and Description
protected boolean	cacheNulls() By default null values returned by resolve(Object) will be cached, meaning that the function won't be called again for keys for which it was determined that there is no value associated.
V	get(K key) The cached entry is most probably a hash of some sort.
protected int	getMaximumSize() This function gives the maximum number of entries that are allowed in the cache.
int	getRefreshTime() The desired refresh time, in seconds.
void	refresh() Update the contents of the cache entry.
V	refresh(K key) Force a refresh of this key.
void	remove(K key) Remove the entry for this key, so that the next request will force a refresh, of this key only.
protected abstract V	resolve(K key) You should implement here a way of finding out the value for a given key.

Methods inherited from class java.lang.Object

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

Constructor Detail

GenericLastValuesCache

public GenericLastValuesCache()

Method Detail

getMaximumSize

protected int getMaximumSize()

This function gives the maximum number of entries that are allowed in the cache.

Returns:

1000 in the default implementation, override for a custom cache size

cacheNulls

protected boolean cacheNulls()

By default null values returned by resolve(Object) will be cached, meaning that the function won't be called again for keys for which it was determined that there is no value associated. You can override this function to return false if you don't want to cache null return values but keep asking for the missing value until there is a positive answer.

Returns:

true to enable null caching, false to disable it.

get

public V get(K key)

Description copied from interface: CacheElement

The cached entry is most probably a hash of some sort. This is why the get() method is specified in this interface, to provide an easy and uniform way of retrieving the data between all the implementations.

Specified by:

get in interface CacheElement<K,V>

Parameters:

key - some unique key

Returns:

the value associated with that key, if any, or null.

resolve

protected abstract V resolve(K key)

You should implement here a way of finding out the value for a given key. Can return null if there is no value for the given key.

Parameters:

key -

Returns:

the value for the given key.

remove

public void remove(K key)

Remove the entry for this key, so that the next request will force a refresh, of this key only.

Parameters:

key - key to remove

refresh

public V refresh(K key)

Force a refresh of this key. To be used for example with null-enabled caches when a key that didn't have a value until now has been defined and the cache for this entry must be refreshed. Or when the value has changed of course.

Parameters:

key -

Returns:

new value for this key

refresh

public void refresh()

Description copied from interface: CacheElement

Update the contents of the cache entry. The implementation is application-dependent. Typically it involves filling an internal hash with some values from the database. But it can do whatever operation here, even something that doesn't involve actually caching anything, but just to execute a periodic task (cron style).

Specified by:

refresh in interface CacheElement<K,V>

getRefreshTime

public int getRefreshTime()

Description copied from interface: CacheElement

The desired refresh time, in seconds. After this much time from the previous update, the CacheElement.refresh() method is called.

Specified by:

getRefreshTime in interface CacheElement<K,V>

Returns:

the number of seconds between the calls to CacheElement.refresh()