org.opencms.cache
Class CmsLruCache

java.lang.Object
  org.opencms.cache.CmsLruCache

public class CmsLruCache
extends java.lang.Object

Implements an LRU (last recently used) cache.

The idea of this cache is 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_CmsLruCacheObject to be notified when they are added/removed from the CmsFlexLruCache.

Since:

6.0.0

Version:

$Revision: 1.29 $

Author:

Thomas Weckert

See Also:

I_CmsLruCacheObject

Constructor Summary

CmsLruCache(long theMaxCacheCosts, long theAvgCacheCosts, int theMaxObjectCosts)
The constructor with all options.

Method Summary

boolean	add(I_CmsLruCacheObject theCacheObject) Adds a new object to this cache.
void	clear() Removes all cached objects in this cache.
long	getAvgCacheCosts() Returns the average costs of all cached objects.
long	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_CmsLruCacheObject	remove(I_CmsLruCacheObject 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.
java.lang.String	toString() Returns a string representing the current state of the cache.
boolean	touch(I_CmsLruCacheObject 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, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

CmsLruCache

public CmsLruCache(long theMaxCacheCosts,
                   long theAvgCacheCosts,
                   int theMaxObjectCosts)

The constructor with all options.

Parameters:

theMaxCacheCosts - the maximum cache costs of all cached objects

theAvgCacheCosts - the average cache costs of all cached objects

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

Method Detail

add

public boolean add(I_CmsLruCacheObject 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

clear

public void clear()

Removes all cached objects in this cache.

getAvgCacheCosts

public long getAvgCacheCosts()

Returns the average costs of all cached objects.

Returns:

the average costs of all cached objects

getMaxCacheCosts

public long 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

remove

public I_CmsLruCacheObject remove(I_CmsLruCacheObject 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

toString

public java.lang.String toString()

Returns a string representing the current state of the cache.

Overrides:

toString in class java.lang.Object

Returns:

a string representing the current state of the cache

touch

public boolean touch(I_CmsLruCacheObject 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

Returns:

true if an object was found and touched