org.datanucleus.enhancer

Class EnhancementHelper

java.lang.Object

org.datanucleus.enhancer.EnhancementHelper

public class EnhancementHelper
extends Object

Helper class for the DN bytecode enhancement contract. It contains methods to register metadata for persistable classes and to perform common operations needed by implementations, not by end users.

It allows construction of instances of persistable classes without using reflection.

Persistable classes register themselves via a static method at class load time. There is no security restriction on this access. TODO Provide a mechanism to automatically deregister classes when their class loader exits? or register against the NucleusContext?

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	EnhancementHelper.RegisterClassListener

Method Summary

Modifier and Type	Method and Description
void	addRegisterClassListener(EnhancementHelper.RegisterClassListener crl) Add the specified RegisterClassListener to the listener list.
static EnhancementHelper	getInstance()
Collection<Class>	getRegisteredClasses() Returns a collection of class objects of the registered persistable classes.
Persistable	newInstance(Class pcClass, StateManager sm) Create a new instance of the class and assign its StateManager.
Persistable	newInstance(Class pcClass, StateManager sm, Object oid) Create a new instance of the class and assign its StateManager and key values from the ObjectId.
Object	newObjectIdInstance(Class pcClass) Create a new instance of the ObjectId class of this Persistable class.
Object	newObjectIdInstance(Class pcClass, Object obj) Create a new instance of the class used by the parameter Class for JDO identity, using the key constructor of the object id class.
static void	registerClass(Class pcClass, Persistable pc) Register metadata by class.
void	removeRegisterClassListener(EnhancementHelper.RegisterClassListener crl) Remove the specified RegisterClassListener from the listener list.
void	unregisterClasses(ClassLoader cl) Unregister all classes for the specified class loader.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static EnhancementHelper getInstance()

newInstance

public Persistable newInstance(Class pcClass,
                               StateManager sm)

Create a new instance of the class and assign its StateManager.

Parameters:

pcClass - the Persistable class.

sm - the StateManager which will own the new instance.

Returns:

the new instance, or null if the class is not registered.

See Also:

Persistable.dnNewInstance(StateManager sm)

newInstance

public Persistable newInstance(Class pcClass,
                               StateManager sm,
                               Object oid)

Create a new instance of the class and assign its StateManager and key values from the ObjectId. If the oid parameter is null, no key values are copied. The new instance has its dnFlags set to LOAD_REQUIRED.

Parameters:

pcClass - the Persistable class.

sm - the StateManager which will own the new instance.

oid - the ObjectId instance from which to copy key field values.

Returns:

the new instance, or null if the class is not registered.

See Also:

Persistable.dnNewInstance(StateManager sm, Object oid)

newObjectIdInstance

public Object newObjectIdInstance(Class pcClass)

Create a new instance of the ObjectId class of this Persistable class. It is intended only for application identity. This method should not be called for classes that use single field identity; newObjectIdInstance(Class, Object) should be used instead. If the class has been enhanced for datastore identity, or if the class is abstract, null is returned.

Parameters:

pcClass - the Persistable class.

Returns:

the new ObjectId instance, or null if the class is not registered.

newObjectIdInstance

public Object newObjectIdInstance(Class pcClass,
                                  Object obj)

Create a new instance of the class used by the parameter Class for JDO identity, using the key constructor of the object id class. It is intended for single field identity. The identity instance returned has no relationship with the values of the primary key fields of the persistence-capable instance on which the method is called. If the key is the wrong class for the object id class, null is returned.

For classes that use single field identity, if the parameter is of one of the following types, the behavior must be as specified:

• Number or Character: the parameter must be the single field type or the wrapper class of the primitive field type; the parameter is passed to the single field identity constructor
• ObjectIdFieldSupplier: the field value is fetched from the ObjectIdFieldSupplier and passed to the single field identity constructor
• String: the String is passed to the single field identity constructor

Parameters:

obj - the Object form of the object id

pcClass - the Persistable class.

Returns:

the new ObjectId instance, or null if the class is not registered.

registerClass

public static void registerClass(Class pcClass,
                                 Persistable pc)

Register metadata by class. This is called by the enhanced constructor of the Persistable class.

Parameters:

pcClass - the Persistable class used as the key for lookup.

pc - an instance of the Persistable class. TODO We can just do pcClass.newInstance() to get one!

unregisterClasses

public void unregisterClasses(ClassLoader cl)

Unregister all classes for the specified class loader.

Parameters:

cl - ClassLoader

addRegisterClassListener

public void addRegisterClassListener(EnhancementHelper.RegisterClassListener crl)

Add the specified RegisterClassListener to the listener list.

Parameters:

crl - the listener to be added

removeRegisterClassListener

public void removeRegisterClassListener(EnhancementHelper.RegisterClassListener crl)

Remove the specified RegisterClassListener from the listener list.

Parameters:

crl - the listener to be removed

getRegisteredClasses

public Collection<Class> getRegisteredClasses()

Returns a collection of class objects of the registered persistable classes.

Returns:

registered persistable classes