org.apache.ojb.broker.cache
Class TwoLevelCache

java.lang.Object
  org.apache.ojb.broker.cache.TwoLevelCache

All Implemented Interfaces:

ObjectCache, PBListener, PBStateListener

public class TwoLevelCache

extends java.lang.Object

implements ObjectCache, PBStateListener

A cache that delegates to another cache in case of misses, and maintains that second-level cache with clones. Work in progress! Known problems:

• If there is a non-proxied collection field in the cached object, then inserting the object causes an extra query to fill that field. :-(
• All references of the cached object are substituted with proxies during caching, even if they are declared non-proxied.
• The code for instantiating proxy references has been copied from other OJB source.
• the second-level cache does not cache collections. Conseqently, iterating thru a collection still requires a database query.
• If an object's class does not have a clone method or does not implement the Cloneable tag interface, then an attempt to use the cache will result in an exception. Alternatively, we might choose to silently ignore that situation.
• the class uses a static map, i.e., one per VM. This map can be cleared only by the static method clearSecondLevel(), thus the usage of this class will infiltrate the (test) code even in case this cache is not used at all.

Version:

$Id: TwoLevelCache.java,v 1.2 2003/11/28 14:40:00 arminw Exp $

Author:

oliverm

See Also:

ObjectCachePerBrokerImpl

Nested Class Summary

(package private) static class

TwoLevelCache.NoCloneMethod

Field Summary

protected Logger	logger
protected java.util.Map	objectTable the hashtable holding all cached objects

Constructor Summary

TwoLevelCache(PersistenceBroker broker, java.util.Properties props)
OJB calls this constructor by reflection.

Method Summary

void	afterBegin(PBStateEvent event) Called after a PersistenceBroker transaction was started.
void	afterCommit(PBStateEvent event) Called after a PersistenceBroker commit was called.
void	afterOpen(PBStateEvent event) Called after the PersistenceBroker instance was obtained from pool.
void	afterRollback(PBStateEvent event) Called after a PersistenceBroker rollback was called.
void	beforeBegin(PBStateEvent event) Called before a PersistenceBroker transaction was started.
void	beforeClose(PBStateEvent event) We clear the cache
void	beforeCommit(PBStateEvent event) Called before a PersistenceBroker commit was called.
void	beforeRollback(PBStateEvent event) Called before a PersistenceBroker rollback was called.
void	cache(Identity oid, java.lang.Object obj) If this method is being called while retrieving the object from database, then the references and collections of obj are filled.
void	clear() Clear ObjectCache.
static void	clearSecondLevel() clear the second level cache, which is shared by all instances in the same VM.
protected java.lang.Object	clone(java.lang.Object in) this method is invoked when an object in inserted or retrieved from the second level.
protected DescriptorRepository	getDescriptorRepository()
protected java.lang.Object	getProxy(java.lang.Class referencedClass, java.lang.Class referencedProxy, java.lang.Object[] pkVals)
protected void	initCacheCollectionField(CollectionDescriptor colDesc, java.lang.Object cacheObj, java.lang.Object origObject) Sets the value of one collection field when an object is inserted into the cache.
protected void	initLookedUpCollections(java.lang.Object obj, java.lang.Object cacheObj) Initializes the the non-embedded collection fields after the object has been retrieved from the cache.
java.lang.Object	lookup(Identity oid) Does an extra lookup in the secondLevelCache if the first lookup fails.
void	remove(Identity oid) Removes an Object from the cache.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

objectTable

protected java.util.Map objectTable

the hashtable holding all cached objects

logger

protected final Logger logger

Constructor Detail

TwoLevelCache

public TwoLevelCache(PersistenceBroker broker,
                     java.util.Properties props)

OJB calls this constructor by reflection.

Parameters:

props - ignored

Method Detail

getDescriptorRepository

protected final DescriptorRepository getDescriptorRepository()

Returns:

the content of the repository.xml or the like.

clear

public void clear()

Clear ObjectCache. I.e. remove all entries for classes and objects. Do not clear the second-level cache

Specified by:

clear in interface ObjectCache

clearSecondLevel

public static void clearSecondLevel()

clear the second level cache, which is shared by all instances in the same VM.

cache

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

If this method is being called while retrieving the object from database, then the references and collections of obj are filled. Problem: if this method is called during insert inside a transaction that is later rolledback, then there are objects entered into the second-level cache that should not be there.

Specified by:

cache in interface ObjectCache

getProxy

protected final java.lang.Object getProxy(java.lang.Class referencedClass,
                                          java.lang.Class referencedProxy,
                                          java.lang.Object[] pkVals)

clone

protected java.lang.Object clone(java.lang.Object in)
                          throws java.lang.CloneNotSupportedException

this method is invoked when an object in inserted or retrieved from the second level. Maybe overridden to do model-specific cloning or the like.

Parameters:

in - some object

Returns:

clone of that object.

Throws:

java.lang.CloneNotSupportedException

initLookedUpCollections

protected void initLookedUpCollections(java.lang.Object obj,
                                       java.lang.Object cacheObj)

Initializes the the non-embedded collection fields after the object has been retrieved from the cache.

Parameters:

obj - the freshly retrieved object

cacheObj - its copy in the cache

initCacheCollectionField

protected void initCacheCollectionField(CollectionDescriptor colDesc,
                                        java.lang.Object cacheObj,
                                        java.lang.Object origObject)

Sets the value of one collection field when an object is inserted into the cache.

Parameters:

colDesc -

cacheObj - the copy of the object in the cache

origObject - the copy of the object in the scope of some PersistenceBroker

lookup

public java.lang.Object lookup(Identity oid)

Does an extra lookup in the secondLevelCache if the first lookup fails.

Specified by:

lookup in interface ObjectCache

See Also:

ObjectCachePerBrokerImpl.lookup(org.apache.ojb.broker.Identity)

toString

public java.lang.String toString()

remove

public void remove(Identity oid)

Removes an Object from the cache.

Specified by:

remove in interface ObjectCache

Parameters:

oid - Identity of the object to be removed.

beforeClose

public void beforeClose(PBStateEvent event)

We clear the cache

Specified by:

beforeClose in interface PBStateListener

afterOpen

public void afterOpen(PBStateEvent event)

Description copied from interface: PBStateListener

Called after the PersistenceBroker instance was obtained from pool.

Specified by:

afterOpen in interface PBStateListener

beforeBegin

public void beforeBegin(PBStateEvent event)

Description copied from interface: PBStateListener

Called before a PersistenceBroker transaction was started.

Specified by:

beforeBegin in interface PBStateListener

afterBegin

public void afterBegin(PBStateEvent event)

Description copied from interface: PBStateListener

Called after a PersistenceBroker transaction was started.

Specified by:

afterBegin in interface PBStateListener

beforeCommit

public void beforeCommit(PBStateEvent event)

Description copied from interface: PBStateListener

Called before a PersistenceBroker commit was called.

Specified by:

beforeCommit in interface PBStateListener

afterCommit

public void afterCommit(PBStateEvent event)

Description copied from interface: PBStateListener

Called after a PersistenceBroker commit was called.

Specified by:

afterCommit in interface PBStateListener

beforeRollback

public void beforeRollback(PBStateEvent event)

Description copied from interface: PBStateListener

Called before a PersistenceBroker rollback was called.

Specified by:

beforeRollback in interface PBStateListener

afterRollback

public void afterRollback(PBStateEvent event)

Description copied from interface: PBStateListener

Called after a PersistenceBroker rollback was called.

Specified by:

afterRollback in interface PBStateListener