lazyj.cache

Class ExpirationCache<K,V>

java.lang.Object

lazyj.cache.ExpirationCache<K,V>

Type Parameters:

K - key type

V - value type

All Implemented Interfaces:

CacheElement<K,V>

Direct Known Subclasses:

PageCache

public class ExpirationCache<K,V>
extends java.lang.Object
implements CacheElement<K,V>

This class implements a caching with a maximum lifetime after which the elements are removed. Optionally the cache can also have a limited size, in which case the least recently used entry will be removed when adding a new entry with the size at the specified limit. For expiration a single thread is used, so try to be fast in processing the callbacks.

Since:

Nov 20, 2007 (1.0.3)

Author:

costing

Constructor Summary

Constructors

Constructor and Description
ExpirationCache() Build an expiration cache of unlimited size.
ExpirationCache(int size) Build an expiration cache with a fixed size.

Method Summary

Methods

Modifier and Type	Method and Description
protected void	callbackOnExpiry(K key, V value) Callback function, to be able to react when something is removed.
V	get(K key) The cached entry is most probably a hash of some sort.
java.util.Set<K>	getKeys() Get the keys currently in the cache
int	getRefreshTime() The desired refresh time, in seconds.
java.util.List<V>	getValues() Get the values in the cache
void	overwrite(K key, V value, long lLifetime) Add a new value in the cache for the given key, overwriting if necessary the previous entry.
void	put(K key, V value, long lLifetime) Put a value in the cache with a maximum lifetime.
void	refresh() Update the contents of the cache entry.
V	remove(K key) Remove an entry from the expiration queue
int	size() Get the cache size

Methods inherited from class java.lang.Object

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

Constructor Detail

ExpirationCache

public ExpirationCache()

Build an expiration cache of unlimited size.

ExpirationCache

public ExpirationCache(int size)

Build an expiration cache with a fixed size.

Parameters:

size - max number of entries in the cache.

Method Detail

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.

remove

public V remove(K key)

Remove an entry from the expiration queue

Parameters:

key -

Returns:

old value, if any

put

public void put(K key,
       V value,
       long lLifetime)

Put a value in the cache with a maximum lifetime. This method will not override an existing cached value!

Parameters:

key -

value -

lLifetime - in milliseconds

See Also:

overwrite(Object, Object, long)

overwrite

public void overwrite(K key,
             V value,
             long lLifetime)

Add a new value in the cache for the given key, overwriting if necessary the previous entry. This will prevent the old entry from expiring, so callbackOnExpiry(Object, Object) will never be called for the entry that is forcefully removed.

Parameters:

key -

value -

lLifetime -

See Also:

put(Object, Object, long)

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()

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>

size

public int size()

Get the cache size

Returns:

the number of entries currently in the cache

getKeys

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

Get the keys currently in the cache

Returns:

the key set

getValues

public java.util.List<V> getValues()

Get the values in the cache

Returns:

list of values in the cache

callbackOnExpiry

protected void callbackOnExpiry(K key,
                    V value)

Callback function, to be able to react when something is removed. Override it to your liking.

Parameters:

key - key that is removed

value - value for the key that is removed