javax.jdo
Class JDOHelper

java.lang.Object
  javax.jdo.JDOHelper

public class JDOHelper

extends java.lang.Object

This class can be used by a JDO-aware application to call the JDO behavior of PersistenceCapable instances without declaring them to be PersistenceCapable. It is also used to acquire a PersistenceManagerFactory via a standard Properties construction.

Every class whose instances can be managed by a JDO PersistenceManager must implement the PersistenceCapable interface.

This helper class defines static methods that allow a JDO-aware application to examine the runtime state of instances. For example, an application can discover whether the instance is persistent, transactional, dirty, new, or deleted; and to get its associated PersistenceManager if it has one.

Version:

1.0.2

Author:

Craig Russell

Constructor Summary

JDOHelper()

Method Summary

static java.lang.Object	getObjectId(java.lang.Object pc) Return a copy of the JDO identity associated with the parameter instance.
static PersistenceManager	getPersistenceManager(java.lang.Object pc) Return the associated PersistenceManager if there is one.
static PersistenceManagerFactory	getPersistenceManagerFactory(java.util.Properties props) Get a PersistenceManagerFactory based on a Properties instance, using the current thread's context class loader to locate the PersistenceManagerFactory class.
static PersistenceManagerFactory	getPersistenceManagerFactory(java.util.Properties props, java.lang.ClassLoader cl) Get a PersistenceManagerFactory based on a Properties instance and a class loader.
static java.lang.Object	getTransactionalObjectId(java.lang.Object pc) Return a copy of the JDO identity associated with the parameter instance.
static boolean	isDeleted(java.lang.Object pc) Tests whether the parameter instance has been deleted.
static boolean	isDirty(java.lang.Object pc) Tests whether the parameter instance is dirty.
static boolean	isNew(java.lang.Object pc) Tests whether the parameter instance has been newly made persistent.
static boolean	isPersistent(java.lang.Object pc) Tests whether the parameter instance is persistent.
static boolean	isTransactional(java.lang.Object pc) Tests whether the parameter instance is transactional.
static void	makeDirty(java.lang.Object pc, java.lang.String fieldName) Explicitly mark the parameter instance and field dirty.

Methods inherited from class java.lang.Object

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

Constructor Detail

JDOHelper

public JDOHelper()

Method Detail

getPersistenceManager

public static PersistenceManager getPersistenceManager(java.lang.Object pc)

Return the associated PersistenceManager if there is one. Transactional and persistent instances return the associated PersistenceManager.

Transient non-transactional instances and instances of classes that do not implement PersistenceCapable return null.

Parameters:

pc - the PersistenceCapable instance.

Returns:

the PersistenceManager associated with the parameter instance.

See Also:

PersistenceCapable.jdoGetPersistenceManager()

makeDirty

public static void makeDirty(java.lang.Object pc,
                             java.lang.String fieldName)

Explicitly mark the parameter instance and field dirty. Normally, PersistenceCapable classes are able to detect changes made to their fields. However, if a reference to an array is given to a method outside the class, and the array is modified, then the persistent instance is not aware of the change. This API allows the application to notify the instance that a change was made to a field.

Transient instances and instances of classes that do not implement PersistenceCapable ignore this method.

Parameters:

pc - the PersistenceCapable instance.

fieldName - the name of the field to be marked dirty.

See Also:

PersistenceCapable.jdoMakeDirty(String fieldName)

getObjectId

public static java.lang.Object getObjectId(java.lang.Object pc)

Return a copy of the JDO identity associated with the parameter instance.

Persistent instances of PersistenceCapable classes have a JDO identity managed by the PersistenceManager. This method returns a copy of the ObjectId that represents the JDO identity.

Transient instances and instances of classes that do not implement PersistenceCapable return null.

The ObjectId may be serialized and later restored, and used with a PersistenceManager from the same JDO implementation to locate a persistent instance with the same data store identity.

If the JDO identity is managed by the application, then the ObjectId may be used with a PersistenceManager from any JDO implementation that supports the PersistenceCapable class.

If the JDO identity is not managed by the application or the data store, then the ObjectId returned is only valid within the current transaction.

Parameters:

pc - the PersistenceCapable instance.

Returns:

a copy of the ObjectId of the parameter instance as of the beginning of the transaction.

See Also:

PersistenceManager.getObjectId(Object pc), PersistenceCapable.jdoGetObjectId(), PersistenceManager.getObjectById(Object oid, boolean validate)

getTransactionalObjectId

public static java.lang.Object getTransactionalObjectId(java.lang.Object pc)

Return a copy of the JDO identity associated with the parameter instance.

Parameters:

pc - the PersistenceCapable instance.

Returns:

a copy of the ObjectId of the parameter instance as modified in this transaction.

See Also:

PersistenceCapable.jdoGetTransactionalObjectId(), PersistenceManager.getObjectById(Object oid, boolean validate)

isDirty

public static boolean isDirty(java.lang.Object pc)

Tests whether the parameter instance is dirty. Instances that have been modified, deleted, or newly made persistent in the current transaction return true.

Transient instances and instances of classes that do not implement PersistenceCapable return false.

Parameters:

pc - the PersistenceCapable instance.

Returns:

true if the parameter instance has been modified in the current transaction.

See Also:

StateManager.makeDirty(PersistenceCapable pc, String fieldName), PersistenceCapable.jdoIsDirty()

isTransactional

public static boolean isTransactional(java.lang.Object pc)

Tests whether the parameter instance is transactional. Instances whose state is associated with the current transaction return true.

Transient instances and instances of classes that do not implement PersistenceCapable return false.

Parameters:

pc - the PersistenceCapable instance.

Returns:

true if the parameter instance is transactional.

See Also:

PersistenceCapable.jdoIsTransactional()

isPersistent

public static boolean isPersistent(java.lang.Object pc)

Tests whether the parameter instance is persistent. Instances that represent persistent objects in the data store return true.

Transient instances and instances of classes that do not implement PersistenceCapable return false.

Parameters:

pc - the PersistenceCapable instance.

Returns:

true if the parameter instance is persistent.

See Also:

PersistenceManager.makePersistent(Object pc), PersistenceCapable.jdoIsPersistent()

isNew

public static boolean isNew(java.lang.Object pc)

Tests whether the parameter instance has been newly made persistent. Instances that have been made persistent in the current transaction return true.

Transient instances and instances of classes that do not implement PersistenceCapable return false.

Parameters:

pc - the PersistenceCapable instance.

Returns:

true if the parameter instance was made persistent in the current transaction.

See Also:

PersistenceManager.makePersistent(Object pc), PersistenceCapable.jdoIsNew()

isDeleted

public static boolean isDeleted(java.lang.Object pc)

Tests whether the parameter instance has been deleted. Instances that have been deleted in the current transaction return true.

Transient instances and instances of classes that do not implement PersistenceCapable return false.

Parameters:

pc - the PersistenceCapable instance.

Returns:

true if the parameter instance was deleted in the current transaction.

See Also:

PersistenceManager.deletePersistent(Object pc), PersistenceCapable.jdoIsDeleted()

getPersistenceManagerFactory

public static PersistenceManagerFactory getPersistenceManagerFactory(java.util.Properties props)

Get a PersistenceManagerFactory based on a Properties instance, using the current thread's context class loader to locate the PersistenceManagerFactory class.

Parameters:

props - a Properties instance with properties of the PersistenceManagerFactory.

Returns:

the PersistenceManagerFactory.

See Also:

getPersistenceManagerFactory(Properties,ClassLoader)

getPersistenceManagerFactory

public static PersistenceManagerFactory getPersistenceManagerFactory(java.util.Properties props,
                                                                     java.lang.ClassLoader cl)

Get a PersistenceManagerFactory based on a Properties instance and a class loader. The following are standard key values:
"javax.jdo.PersistenceManagerFactoryClass"
"javax.jdo.option.Optimistic",
"javax.jdo.option.RetainValues",
"javax.jdo.option.RestoreValues",
"javax.jdo.option.IgnoreCache",
"javax.jdo.option.NontransactionalRead",
"javax.jdo.option.NontransactionalWrite",
"javax.jdo.option.Multithreaded",
"javax.jdo.option.ConnectionUserName",
"javax.jdo.option.ConnectionPassword",
"javax.jdo.option.ConnectionURL",
"javax.jdo.option.ConnectionFactoryName",
"javax.jdo.option.ConnectionFactory2Name".

JDO implementations are permitted to define key values of their own. Any key values not recognized by the implementation must be ignored. Key values that are recognized but not supported by an implementation must result in a JDOFatalUserException thrown by the method.

The returned PersistenceManagerFactory is not configurable (the setXXX methods will throw an exception).

JDO implementations might manage a map of instantiated PersistenceManagerFactory instances based on specified property key values, and return a previously instantiated PersistenceManagerFactory instance. In this case, the properties of the returned instance must exactly match the requested properties.

Parameters:

props - a Properties instance with properties of the PersistenceManagerFactory.

cl - a class loader to use to load the PersistenceManagerFactory class.

Returns:

the PersistenceManagerFactory.