org.osesb.utilities.cache
Class CacheEntry

java.lang.Object
  org.osesb.utilities.cache.CacheEntry

All Implemented Interfaces:

java.lang.Comparable

Direct Known Subclasses:

TextFileCacheEntry

public class CacheEntry
extends java.lang.Object
implements java.lang.Comparable

CacheEntry wraps a cached Object in a SimpleCache. Thread-safe access to CacheEntry properties is the responsibility of SimpleCache.

CachEntry implements Comparable so that cache entries can be sorted by SimpleCache.evict(). For example, if sorted by accessCount, SimpleCache.evict() will remove items in ascending order of accessCount until SimpleCache.size() = SimpleCache.maxCacheSize.

CacheEntry properties that can be used to implement eviction strategies include:

1. CacheEntry.lastAccessedTime: evict based on least recently accessed.

2. CacheEntry.accessCount: evict based on least frequently accessed.

Since:

Version .9

Field Summary

long	accessCount The number of times that this object was accessed.
static java.lang.String	ACCESSCOUNT_EVICTIONSTRATEGY
protected java.lang.Object	cachedObject The cached Object.
protected java.lang.String	cacheKey The cached Object's key.
protected java.lang.reflect.Field	compareField The Field for Comparable interface method compareTo().
long	lastAccessedTime The last time that this object was accessed.
static java.lang.String	LASTACCESSTIME_EVICTIONSTRATEGY
protected static org.apache.commons.logging.Log	log The logging implementation for this class.
protected java.lang.String	thisClassName The full name of this class.
protected java.text.SimpleDateFormat	toStringSDF
protected java.util.Date	toStringTime

Constructor Summary

CacheEntry(java.lang.String cacheKey, java.lang.Object cachedObject)
Constructs a CacheEntry object

Method Summary

int	compareTo(java.lang.Object other) Compares this cacheEntry to another (Comparable Interface).
long	getAccessCount() Return the cache entry's access count.
java.lang.Object	getCachedObject() Return the cached Object.
java.lang.String	getCacheKey() Return the cached Object's key.
java.lang.String	getCompareFieldName() Return the cache entry's compareTo() field name.
long	getLastAccessedTime() Return the cache entry's lastAccessedTime stamp.
void	incrementAccessCount() Increment the cache entry's access count.
void	setAccessCount(long accessCount) Set the cache entry's access count.
void	setCompareField(java.lang.String compareFieldName) Set the cache entry's compareTo() field name.
void	setLastAccessedTime(long lastAccessedTime) Set the cache entry's lastAccessedTime stamp.
java.lang.String	toString() Returns the String representation of this CacheEntry.

Methods inherited from class java.lang.Object

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

Field Detail

log

protected static org.apache.commons.logging.Log log

The logging implementation for this class.

cachedObject

protected java.lang.Object cachedObject

The cached Object.

cacheKey

protected java.lang.String cacheKey

The cached Object's key. We need the cache key because SimpleCache.evict() iterates through cache entries in ascending order of the 'evictionStrategyField'. The evict() method needs access to CacheEntry keys in order to remove 'stale' CacheEntry(s).

lastAccessedTime

public long lastAccessedTime

The last time that this object was accessed.

accessCount

public long accessCount

The number of times that this object was accessed.

compareField

protected java.lang.reflect.Field compareField

The Field for Comparable interface method compareTo(). SimpleCache.put() sets this field according to the 'evictionStrategyField' element of the SimpleCache configuration.

'lastAccessedTime' and 'accessCount' can be used as eviction strategy fields. Eviction strategy fields must be 'public'.

SimpleCache.evict() sorts cache entries based on this field, and evicts entries in ascending order until the cache size equals maxCacheSize.

LASTACCESSTIME_EVICTIONSTRATEGY

public static java.lang.String LASTACCESSTIME_EVICTIONSTRATEGY

ACCESSCOUNT_EVICTIONSTRATEGY

public static java.lang.String ACCESSCOUNT_EVICTIONSTRATEGY

thisClassName

protected java.lang.String thisClassName

The full name of this class.

toStringSDF

protected java.text.SimpleDateFormat toStringSDF

toStringTime

protected java.util.Date toStringTime

Constructor Detail

CacheEntry

public CacheEntry(java.lang.String cacheKey,
                  java.lang.Object cachedObject)
           throws java.lang.Exception

Constructs a CacheEntry object

Parameters:

cachedObject - The object to cache.

Throws:

java.lang.Exception - if cachedObject is null.

Method Detail

getCachedObject

public java.lang.Object getCachedObject()

Return the cached Object.

Returns:

the cached Object.

getCacheKey

public java.lang.String getCacheKey()

Return the cached Object's key.

Returns:

the cached Object's key.

setLastAccessedTime

public void setLastAccessedTime(long lastAccessedTime)

Set the cache entry's lastAccessedTime stamp.

Parameters:

lastAccessedTime - The cache entry's lastAccessedTime stamp.

getLastAccessedTime

public long getLastAccessedTime()

Return the cache entry's lastAccessedTime stamp.

Returns:

the cache entry's lastAccessedTime stamp.

setAccessCount

public void setAccessCount(long accessCount)

Set the cache entry's access count.

Parameters:

accessCount - The cache entry's access count.

getAccessCount

public long getAccessCount()

Return the cache entry's access count.

Returns:

the cache entry's access count.

incrementAccessCount

public void incrementAccessCount()

Increment the cache entry's access count.

setCompareField

public void setCompareField(java.lang.String compareFieldName)

Set the cache entry's compareTo() field name. Useful for eviction strategy.

Parameters:

compareFieldName - The name of cache entry's compareTo() field.

getCompareFieldName

public java.lang.String getCompareFieldName()

Return the cache entry's compareTo() field name.

Returns:

the cache entry's compareTo() field name.

compareTo

public int compareTo(java.lang.Object other)

Compares this cacheEntry to another (Comparable Interface). compareTo() is used by the default eviction strategies.

Specified by:

compareTo in interface java.lang.Comparable

Parameters:

other - The CacheEntry for the comparison.

Returns:

an int consistent with comparison rules.

toString

public java.lang.String toString()

Returns the String representation of this CacheEntry.

Overrides:

toString in class java.lang.Object

Returns:

the String representation of this CacheEntry.