oracle.toplink.essentials.internal.identitymaps

Class HardCacheWeakIdentityMap

java.lang.Object

oracle.toplink.essentials.internal.identitymaps.IdentityMap

oracle.toplink.essentials.internal.identitymaps.FullIdentityMap

oracle.toplink.essentials.internal.identitymaps.WeakIdentityMap

oracle.toplink.essentials.internal.identitymaps.HardCacheWeakIdentityMap

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable

Direct Known Subclasses:

SoftCacheWeakIdentityMap

public class HardCacheWeakIdentityMap
extends WeakIdentityMap

Purpose: A weak cache is identical to the weak identity map, however the weak can be a performance problem for some types of apps because it can cause too much garbage collection of objects read causing them to be re-read and re-built (this defeats the purpose of the cache). The weak cache solves this through also holding a fixed number of objects is memory to improve caching. This makes used of an exposed node linked list to maintain the objects by storing the link nodes in the cache key.

Responsibilities:

• Guarantees identity
• Allows garbage collection
• Increases performance through maintaining a fixed size cache of MRU objects when memory is available
• The default size of the reference cache is half the max size

Since:

TOPLink/Java 1.2

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	HardCacheWeakIdentityMap.ReferenceCacheKey Inner class to define the specialized weak cache key.

Field Summary

Fields

Modifier and Type	Field and Description
protected ExposedNodeLinkedList	referenceCache

Fields inherited from class oracle.toplink.essentials.internal.identitymaps.WeakIdentityMap

cleanupCount, cleanupSize

Fields inherited from class oracle.toplink.essentials.internal.identitymaps.FullIdentityMap

cacheKeys

Fields inherited from class oracle.toplink.essentials.internal.identitymaps.IdentityMap

maxSize, searchKey

Constructor Summary

Constructors

Constructor and Description
HardCacheWeakIdentityMap(int size)

Method Summary

Modifier and Type	Method and Description
java.lang.Object	buildReference(java.lang.Object object) Creates a Soft reference if Required
CacheKey	createCacheKey(java.util.Vector primaryKey, java.lang.Object object, java.lang.Object writeLockValue, long readTime) Use a ReferenceCacheKey that also stores the linked list node to manage the LRU sub-cache of references.
ExposedNodeLinkedList	getReferenceCache() Return the linked reference cache.
boolean	hasReference(java.lang.Object reference) Checks if the object is null, or reference's object is null.
protected void	put(CacheKey cacheKey) Store the object in the cache with the cache key.
java.lang.Object	remove(CacheKey cacheKey) Remove the cache key from the map and the sub-cache list.
void	updateMaxSize(int maxSize) This method will be used to update the max cache size.

Methods inherited from class oracle.toplink.essentials.internal.identitymaps.WeakIdentityMap

cleanupDeadCacheKeys, getCleanupCount, getCleanupSize, setCleanupCount, setCleanupSize

Methods inherited from class oracle.toplink.essentials.internal.identitymaps.FullIdentityMap

clone, collectLocks, elements, getCacheKey, getCacheKeys, getSize, getSize, keys, put, resetCacheKey, resetCacheKey, setCacheKeys

Methods inherited from class oracle.toplink.essentials.internal.identitymaps.IdentityMap

acquireDeferredLock, acquireLock, acquireLockNoWait, acquireReadLockOnCacheKey, acquireReadLockOnCacheKeyNoWait, containsKey, createCacheKey, get, getCacheKey, getCacheKeyWithReadLock, getDefaultIdentityMapClass, getMaxSize, getSearchKey, getWrapper, getWriteLockValue, initialize, remove, setMaxSize, setSearchKey, setWrapper, setWriteLockValue, toString, updateCacheKey

Methods inherited from class java.lang.Object

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

Field Detail

referenceCache

protected ExposedNodeLinkedList referenceCache

Constructor Detail

HardCacheWeakIdentityMap

public HardCacheWeakIdentityMap(int size)

Method Detail

createCacheKey

public CacheKey createCacheKey(java.util.Vector primaryKey,
                               java.lang.Object object,
                               java.lang.Object writeLockValue,
                               long readTime)

Use a ReferenceCacheKey that also stores the linked list node to manage the LRU sub-cache of references.

Overrides:

createCacheKey in class WeakIdentityMap

getReferenceCache

public ExposedNodeLinkedList getReferenceCache()

Return the linked reference cache.

buildReference

public java.lang.Object buildReference(java.lang.Object object)

Creates a Soft reference if Required

Parameters:

object - is the domain object to cache.

hasReference

public boolean hasReference(java.lang.Object reference)

Checks if the object is null, or reference's object is null.

Parameters:

the - object for hard or the reference for soft.

put

protected void put(CacheKey cacheKey)

Store the object in the cache with the cache key. Also store the linked list node in the cache key.

Overrides:

put in class WeakIdentityMap

remove

public java.lang.Object remove(CacheKey cacheKey)

Remove the cache key from the map and the sub-cache list.

Overrides:

remove in class FullIdentityMap

Returns:

The object held within the CacheKey or null if no object cached for given primaryKey

updateMaxSize

public void updateMaxSize(int maxSize)

This method will be used to update the max cache size.

Overrides:

updateMaxSize in class IdentityMap