org.jboss.util
Class TimedCachePolicy

java.lang.Object
  |
  +--java.util.TimerTask
        |
        +--org.jboss.util.TimedCachePolicy

All Implemented Interfaces:

CachePolicy, java.lang.Runnable, Service

public class TimedCachePolicy

extends java.util.TimerTask

implements CachePolicy

An implementation of a timed cache. This is a cache whose entries have a limited lifetime with the ability to refresh their lifetime. The entries managed by the cache implement the TimedCachePolicy.TimedEntry interface. If an object inserted into the cache does not implement this interface, it will be wrapped in a DefaultTimedEntry and will expire without the possibility of refresh after getDefaultLifetime() seconds. This is a lazy cache policy in that objects are not checked for expiration until they are accessed.

Version:

$Revision: 1.1 $

Author:

Scott_Stark@displayscape.com

Inner Class Summary

static interface

TimedCachePolicy.TimedEntry The interface that cache entries support.

Field Summary

protected int	defaultLifetime The lifetime in seconds to use for objects inserted that do not implement the TimedEntry interface.
protected java.util.Map	entryMap The map of cached TimedEntry objects.
protected long	now The caches notion of the current time
protected int	resolution The resolution in seconds of the cach current time
protected static java.util.Timer	resolutionTimer
protected boolean	threadSafe A flag indicating if entryMap should be synchronized

Constructor Summary

TimedCachePolicy()
Creates a new TimedCachePolicy with a default entry lifetime of 30 mins that does not synchronized access to its policy store and uses a 60 second resolution.

TimedCachePolicy(int defaultLifetime)
Creates a new TimedCachePolicy with the given default entry lifetime that does not synchronized access to its policy store and uses a 60 second resolution.

TimedCachePolicy(int defaultLifetime, boolean threadSafe, int resolution)
Creates a new TimedCachePolicy with the given default entry lifetime that does/does not synchronized access to its policy store depending on the value of threadSafe.

Method Summary

long	currentTimeMillis() Get the cache time.
void	destroy() Clears the cache of all entries.
void	flush() Remove all entries from the cache.
java.lang.Object	get(java.lang.Object key) Get the cache value for key if it has not expired.
void	init() Initializes the cache for use.
void	insert(java.lang.Object key, java.lang.Object value) Insert a value into the cache.
java.lang.Object	peek(java.lang.Object key) Get the cache value for key.
TimedCachePolicy.TimedEntry	peekEntry(java.lang.Object key) Get the raw TimedEntry for key without performing any expiration check.
void	remove(java.lang.Object key) Remove the entry associated with key.
void	run() The TimerTask run method.
void	start() Schedules this with the class resolutionTimer Timer object for execution every resolution seconds.
void	stop() Stop cancels the resolution timer and flush()es the cache.

Methods inherited from class java.util.TimerTask

cancel, scheduledExecutionTime

Methods inherited from class java.lang.Object

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

Field Detail

resolutionTimer

protected static java.util.Timer resolutionTimer

entryMap

protected java.util.Map entryMap

The map of cached TimedEntry objects.

defaultLifetime

protected int defaultLifetime

The lifetime in seconds to use for objects inserted that do not implement the TimedEntry interface.

threadSafe

protected boolean threadSafe

A flag indicating if entryMap should be synchronized

now

protected long now

The caches notion of the current time

resolution

protected int resolution

The resolution in seconds of the cach current time

Constructor Detail

TimedCachePolicy

public TimedCachePolicy()

Creates a new TimedCachePolicy with a default entry lifetime of 30 mins that does not synchronized access to its policy store and uses a 60 second resolution.

TimedCachePolicy

public TimedCachePolicy(int defaultLifetime)

Creates a new TimedCachePolicy with the given default entry lifetime that does not synchronized access to its policy store and uses a 60 second resolution.

TimedCachePolicy

public TimedCachePolicy(int defaultLifetime,
                        boolean threadSafe,
                        int resolution)

Creates a new TimedCachePolicy with the given default entry lifetime that does/does not synchronized access to its policy store depending on the value of threadSafe.

Parameters:

defaultLifetime, - the lifetime in seconds to use for objects inserted that do not implement the TimedEntry interface.

threadSafe, - a flag indicating if the cach store should be synchronized to allow correct operation under multi-threaded access. If true, the cache store is synchronized. If false the cache store is unsynchronized and the cache is not thread safe.

resolution, - the resolution in seconds of the cache timer. A cache does not query the system time on every get() invocation. Rather the cache updates its notion of the current time every 'resolution' seconds.

Method Detail

init

public void init()

Initializes the cache for use. Prior to this the cache has no store.

Specified by:

init in interface Service

start

public void start()

Schedules this with the class resolutionTimer Timer object for execution every resolution seconds.

Specified by:

start in interface Service

stop

public void stop()

Stop cancels the resolution timer and flush()es the cache.

Specified by:

stop in interface Service

destroy

public void destroy()

Clears the cache of all entries.

Specified by:

destroy in interface Service

get

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

Get the cache value for key if it has not expired.

Specified by:

get in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

See Also:

CachePolicy.peek(java.lang.Object)

peek

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

Get the cache value for key. This method does not check to see if the entry has expired.

Specified by:

peek in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

See Also:

CachePolicy.get(java.lang.Object)

insert

public void insert(java.lang.Object key,
                   java.lang.Object value)

Insert a value into the cache. In order to have the cache entry reshresh itself value would have to implement TimedEntry and implement the required refresh() method logic.

Specified by:

insert in interface CachePolicy

Parameters:

key, - the key for the cache entry

value, - Either an instance of TimedEntry that will be inserted without change, or an abitrary value that will be wrapped in a non-refreshing TimedEntry.

remove

public void remove(java.lang.Object key)

Remove the entry associated with key.

Specified by:

remove in interface CachePolicy

Following copied from interface: org.jboss.util.CachePolicy

Parameters:

key - the key paired with the object

See Also:

CachePolicy.insert(java.lang.Object, java.lang.Object)

flush

public void flush()

Remove all entries from the cache.

Specified by:

flush in interface CachePolicy

run

public void run()

The TimerTask run method. It updates the cache time to the current system time.

Overrides:

run in class java.util.TimerTask

currentTimeMillis

public long currentTimeMillis()

Get the cache time.

Returns:

the cache time last obtained from System.currentTimeMillis()

peekEntry

public TimedCachePolicy.TimedEntry peekEntry(java.lang.Object key)

Get the raw TimedEntry for key without performing any expiration check.

Returns:

the TimedEntry value associated with key if one exists, null otherwise.