com.opencms.flex.util
Class CmsFlexLruCache

java.lang.Object
  |
  +--com.opencms.flex.util.CmsFlexLruCache

public class CmsFlexLruCache

extends Object

Implements an LRU (last recently used) cache.

The idea of this cache to separate the caching policy from the data structure where the cached objects are stored. The advantage of doing so is, that the CmsFlexLruCache can identify the last-recently-used object in O(1), whereas you would need at least O(n) to traverse the data structure that stores the cached objects. Second, you can easily use the CmsFlexLruCache to get an LRU cache, no matter what data structure is used to store your objects.

The cache policy is affected by the "costs" of the objects being cached. Valuable cache costs might be the byte size of the cached objects for example.

To add/remove cached objects from the data structure that stores them, the objects have to implement the methods defined in the interface I_CmsFlexLruCacheObject to be notified when they are added/removed from the CmsFlexLruCache.

Version:

$Revision: 1.13 $

Author:

Thomas Weckert (t.weckert@alkacon.com)

See Also:

I_CmsFlexLruCacheObject

Constructor Summary

CmsFlexLruCache(int theMaxCacheCosts, int theAvgCacheCosts)
Constructor for a LRU cache with forced garbage collection/finalization, the max. allowed costs of cacheable objects is 1/4 of the max. costs of all cached objects.

CmsFlexLruCache(int theMaxCacheCosts, int theAvgCacheCosts, boolean forceFinalization)
Constructor for a LRU cache where the max. allowed costs of cacheable objects is 1/4 of the max. costs of all cached objects.

CmsFlexLruCache(int theMaxCacheCosts, int theAvgCacheCosts, int theMaxObjectCosts)
Constructor for a LRU cache with forced garbage collection/finalization.

CmsFlexLruCache(int theMaxCacheCosts, int theAvgCacheCosts, int theMaxObjectCosts, boolean forceFinalization)
The constructor with all options.

Method Summary

boolean	add(I_CmsFlexLruCacheObject theCacheObject) Adds a new object to this cache.
void	clear() Removes all cached objects in this cache.
protected void	finalize() Clears this cache for finalization.
int	getAvgCacheCosts() Returns the average costs of all cached objects.
int	getMaxCacheCosts() Returns the max costs of all cached objects.
int	getMaxObjectCosts() Returns the max allowed costs per cached object.
int	getObjectCosts() Returns the current costs of all cached objects.
I_CmsFlexLruCacheObject	remove(I_CmsFlexLruCacheObject theCacheObject) Removes an object from the list of all cached objects in this cache, no matter what position it has inside the list.
int	size() Returns the count of all cached objects.
String	toString() Returns a string representing the current state of the cache.
boolean	touch(I_CmsFlexLruCacheObject theCacheObject) Touch an existing object in this cache, in the sense that it's "last-recently-used" state is updated.

Methods inherited from class java.lang.Object

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

Constructor Detail

CmsFlexLruCache

public CmsFlexLruCache(int theMaxCacheCosts,
                       int theAvgCacheCosts,
                       int theMaxObjectCosts,
                       boolean forceFinalization)

The constructor with all options.

Parameters:

theMaxCacheCosts - the max. cache costs of all cached objects

theAvgCacheCosts - the avg. cache costs of all cached objects

theMaxObjectCosts - the max. allowed cache costs per object. Set theMaxObjectCosts to -1 if you don't want to limit the max. allowed cache costs per object

forceFinalization - should be true if a system wide garbage collection/finalization is forced after objects were removed from the cache

CmsFlexLruCache

public CmsFlexLruCache(int theMaxCacheCosts,
                       int theAvgCacheCosts,
                       int theMaxObjectCosts)

Constructor for a LRU cache with forced garbage collection/finalization.

Parameters:

theMaxCacheCosts - the max. cache costs of all cached objects

theAvgCacheCosts - the avg. cache costs of all cached objects

theMaxObjectCosts - the max. allowed cache costs per object. Set theMaxObjectCosts to -1 if you don't want to limit the max. allowed cache costs per object

CmsFlexLruCache

public CmsFlexLruCache(int theMaxCacheCosts,
                       int theAvgCacheCosts)

Constructor for a LRU cache with forced garbage collection/finalization, the max. allowed costs of cacheable objects is 1/4 of the max. costs of all cached objects.

Parameters:

theMaxCacheCosts - the max. cache costs of all cached objects

theAvgCacheCosts - the avg. cache costs of all cached objects

CmsFlexLruCache

public CmsFlexLruCache(int theMaxCacheCosts,
                       int theAvgCacheCosts,
                       boolean forceFinalization)

Constructor for a LRU cache where the max. allowed costs of cacheable objects is 1/4 of the max. costs of all cached objects.

Parameters:

theMaxCacheCosts - the max. cache costs of all cached objects

theAvgCacheCosts - the avg. cache costs of all cached objects

forceFinalization - should be true if a system wide garbage collection/finalization is forced after objects were removed from the cache

Method Detail

toString

public String toString()

Returns a string representing the current state of the cache.

Overrides:

toString in class Object

add

public boolean add(I_CmsFlexLruCacheObject theCacheObject)

Adds a new object to this cache.

If add the same object more than once, the object is touched instead.

Parameters:

theCacheObject - the object being added to the cache

Returns:

true if the object was added to the cache, false if the object was denied because its cache costs were higher than the allowed max. cache costs per object

touch

public boolean touch(I_CmsFlexLruCacheObject theCacheObject)

Touch an existing object in this cache, in the sense that it's "last-recently-used" state is updated.

Parameters:

theCacheObject - the object being touched

remove

public I_CmsFlexLruCacheObject remove(I_CmsFlexLruCacheObject theCacheObject)

Removes an object from the list of all cached objects in this cache, no matter what position it has inside the list.

Parameters:

theCacheObject - the object being removed from the list of all cached objects

Returns:

a reference to the object that was removed

size

public int size()

Returns the count of all cached objects.

Returns:

the count of all cached objects

finalize

protected void finalize()
                 throws Throwable

Clears this cache for finalization.

Overrides:

finalize in class Object

Throwable

clear

public void clear()

Removes all cached objects in this cache.

getAvgCacheCosts

public int getAvgCacheCosts()

Returns the average costs of all cached objects.

Returns:

the average costs of all cached objects

getMaxCacheCosts

public int getMaxCacheCosts()

Returns the max costs of all cached objects.

Returns:

the max costs of all cached objects

getMaxObjectCosts

public int getMaxObjectCosts()

Returns the max allowed costs per cached object.

Returns:

the max allowed costs per cached object

getObjectCosts

public int getObjectCosts()

Returns the current costs of all cached objects.

Returns:

the current costs of all cached objects