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ojb.broker.accesslayer
Class ObjectCache  

java.lang.Object
  ojb.broker.accesslayer.ObjectCache

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public class ObjectCache

extends java.lang.Object

The ObjectCache stores all Objects loaded by the PersistenceBroker from a DB. When the PersistenceBroker tries to get an Object by its Primary key values it first lookups the cache if the object has been already loaded and cached. Using an ObjectCache has several advantages: - it increases performance as it reduces DB lookups. - it allows to perform circular lookups (as by crossreferenced objects) that would result in non-terminating loops without such a cache. - it maintains the uniqueness of objects as any Db row will be mapped to exactly one object. The cache uses soft-references which allows objects (softly) referenced by the cache to be reclaimed by the Java Garbage Collector when they are not longer referenced elsewhere.

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Field Summary
private static boolean	_debug           debugging flag, false by default = no debugging
private static ObjectCache	_instance           singleton instance
private static java.lang.String	DIDNT_USE
private  java.util.Hashtable	objectTable           the hashtable holding all cached object
private static boolean	USE_CACHE           en/disables cache
private static java.lang.String	USED

 

Constructor Summary
private	ObjectCache()           Constructor declaration

 

Method Summary
void	cache(ojb.broker.Identity oid, java.lang.Object obj)           makes object persistent to the Objectcache.
void	cache(java.lang.Object obj)           Make object obj persistent to Objectcache.
void	clear()           clear ObjectCache.
static ObjectCache	getInstance()           return the singleton instance
static boolean	isCacheUsed()           Insert the method's description here.
java.lang.Object	lookup(ojb.broker.Identity oid)           Lookup object with Identity oid in objectTable.
void	remove(ojb.broker.Identity oid)           removes an Object from the cache.
static void	setCacheUsed(boolean newUSE_CACHE)           sets the flag USE_CACHE to the specified value.
static void	setDebug(boolean b)           set the debugging flag to true to enable debugging

 

Methods inherited from class java.lang.Object

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

 

Field Detail

_debug

private static boolean _debug

debugging flag, false by default = no debugging

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_instance

private static ObjectCache _instance

singleton instance

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DIDNT_USE

private static java.lang.String DIDNT_USE

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objectTable

private java.util.Hashtable objectTable

the hashtable holding all cached object

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USE_CACHE

private static boolean USE_CACHE

en/disables cache

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USED

private static java.lang.String USED

Constructor Detail

ObjectCache

private ObjectCache()

Constructor declaration

Method Detail

setDebug

public static void setDebug(boolean b)

set the debugging flag to true to enable debugging

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getInstance

public static ObjectCache getInstance()

return the singleton instance

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cache

public void cache(java.lang.Object obj)
           throws ojb.broker.ClassNotPersistenceCapableException

Make object obj persistent to Objectcache. compute objects identity and use it as key for the hashmap

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clear

public void clear()

clear ObjectCache. I.e. remove all entries for classes and objects.

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cache

public void cache(ojb.broker.Identity oid,
                  java.lang.Object obj)

makes object persistent to the Objectcache. I'm using soft-references to allow gc reclaim unused objects even if they are still cached.

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isCacheUsed

public static boolean isCacheUsed()

Insert the method's description here. Creation date: (20.11.2000 11:12:42)

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lookup

public java.lang.Object lookup(ojb.broker.Identity oid)

Lookup object with Identity oid in objectTable. returns null if no matching id is found

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remove

public void remove(ojb.broker.Identity oid)

removes an Object from the cache.

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setCacheUsed

public static void setCacheUsed(boolean newUSE_CACHE)

sets the flag USE_CACHE to the specified value. if USE_CACHE is true caching is enabled, if false caching is disabled

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