javax.jdo
Class JDOImplHelper

java.lang.Object
  |
  +--javax.jdo.JDOImplHelper

public class JDOImplHelper

extends java.lang.Object

This class is a helper class for JDO implementations. It contains methods to register metadata for persistence-capable classes and to perform common operations needed by implementations, not by end users.

JDOImplHelper allows construction of instances of persistence-capable classes without using reflection.

Persistence-capable classes register themselves via a static method at class load time. There is no security restriction on this access. JDO implementations get access to the functions provided by this class only if they are authorized by the security manager. To avoid having every call go through the security manager, only the call to get an instance is checked. Once an implementation has an instance, any of the methods can be invoked without security checks.

Version:

0.9

Author:

clr

Nested Class Summary

(package private) static class

JDOImplHelper.Meta This is a helper class to manage metadata per persistence-capable class.

Method Summary

void	copyKeyFieldsToObjectId(java.lang.Class pcClass, PersistenceCapable.ObjectIdFieldManager fm, java.lang.Object oid) Copy fields from an outside source to the key fields in the ObjectId.
void	copyKeyFieldsToObjectId(PersistenceCapable pc, java.lang.Object oid) Copy fields from the PersistenceCapable instance to the Object Id instance.
byte[]	getFieldFlags(java.lang.Class pcClass) Get the field flags for a PersistenceCapable class.
java.lang.String[]	getFieldNames(java.lang.Class pcClass) Get the field names for a PersistenceCapable class.
java.lang.Class[]	getFieldTypes(java.lang.Class pcClass) Get the field types for a PersistenceCapable class.
static JDOImplHelper	getInstance() Get an instance of JDOImplHelper.
java.lang.Class	getPersistenceCapableSuperclass(java.lang.Class pcClass) Get the persistence-capable superclass for a PersistenceCapable class.
PersistenceCapable	newInstance(java.lang.Class pcClass, StateManager sm) Create a new instance of the class and assign its jdoStateManager.
PersistenceCapable	newInstance(java.lang.Class pcClass, StateManager sm, java.lang.Object oid) Create a new instance of the class and assign its jdoStateManager and key values from the ObjectId.
java.lang.Object	newObjectIdInstance(java.lang.Class pcClass) Create a new instance of the ObjectId class of this PersistenceCapable class.
static void	registerClass(java.lang.Class pcClass, java.lang.String[] fieldNames, java.lang.Class[] fieldTypes, byte[] fieldFlags, java.lang.Class persistenceCapableSuperclass, PersistenceCapable pc) Register metadata by class.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static JDOImplHelper getInstance()
                                 throws java.lang.IllegalAccessException

Get an instance of JDOImplHelper. This method checks that the caller is authorized for JDOPermission("getMetadata"), and if not, throws IllegalAccessException.

Returns:

an instance of JDOImplHelper.

Throws:

java.lang.IllegalAccessException

getFieldNames

public java.lang.String[] getFieldNames(java.lang.Class pcClass)

Get the field names for a PersistenceCapable class. The order of fields is the natural ordering of the String class (without considering localization).

Parameters:

pcClass - the PersistenceCapable class.

Returns:

the field names for the class.

getFieldTypes

public java.lang.Class[] getFieldTypes(java.lang.Class pcClass)

Get the field types for a PersistenceCapable class. The order of fields is the same as for field names.

Parameters:

pcClass - the PersistenceCapable class.

Returns:

the field types for the class.

getFieldFlags

public byte[] getFieldFlags(java.lang.Class pcClass)

Get the field flags for a PersistenceCapable class. The order of fields is the same as for field names.

Parameters:

pcClass - the PersistenceCapable class.

Returns:

the field types for the class.

getPersistenceCapableSuperclass

public java.lang.Class getPersistenceCapableSuperclass(java.lang.Class pcClass)

Get the persistence-capable superclass for a PersistenceCapable class.

Parameters:

pcClass - the PersistenceCapable class.

Returns:

the field types for the class.

newInstance

public PersistenceCapable newInstance(java.lang.Class pcClass,
                                      StateManager sm)

Create a new instance of the class and assign its jdoStateManager. The new instance has its jdoFlags set to LOAD_REQUIRED.

Parameters:

pcClass - the PersistenceCapable class.

sm - the StateManager which will own the new instance.

Returns:

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

See Also:

PersistenceCapable.jdoNewInstance(StateManager sm)

newInstance

public PersistenceCapable newInstance(java.lang.Class pcClass,
                                      StateManager sm,
                                      java.lang.Object oid)

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

Parameters:

pcClass - the PersistenceCapable 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:

PersistenceCapable.jdoNewInstance(StateManager sm, Object oid)

newObjectIdInstance

public java.lang.Object newObjectIdInstance(java.lang.Class pcClass)

Create a new instance of the ObjectId class of this PersistenceCapable class.

Parameters:

pcClass - the PersistenceCapable class.

Returns:

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

copyKeyFieldsToObjectId

public void copyKeyFieldsToObjectId(java.lang.Class pcClass,
                                    PersistenceCapable.ObjectIdFieldManager fm,
                                    java.lang.Object oid)

Copy fields from an outside source to the key fields in the ObjectId. This method is generated in the PersistenceCapable class to generate a call to the field manager for each key field in the ObjectId.

For example, an ObjectId class that has three key fields (int id, String name, and Float salary) would have the method generated:

void copyKeyFieldsToObjectId (Object oid, ObjectIdFieldManager fm) {

oid.id = fm.fetchIntField (0);

oid.name = fm.fetchStringField (1);

oid.salary = fm.fetchObjectField (2);

}

The implementation is responsible for implementing the ObjectIdFieldManager to produce the values for the key fields.

Parameters:

pcClass - the PersistenceCapable Class.

oid - the ObjectId target of the copy.

fm - the field manager that supplies the field values.

copyKeyFieldsToObjectId

public void copyKeyFieldsToObjectId(PersistenceCapable pc,
                                    java.lang.Object oid)

Copy fields from the PersistenceCapable instance to the Object Id instance.

Parameters:

pc - the PersistenceCapable source of the key fields

oid - the ObjectId target of the key fields

registerClass

public static void registerClass(java.lang.Class pcClass,
                                 java.lang.String[] fieldNames,
                                 java.lang.Class[] fieldTypes,
                                 byte[] fieldFlags,
                                 java.lang.Class persistenceCapableSuperclass,
                                 PersistenceCapable pc)

Register metadata by class. The registration will be done in the class named JDOImplHelper loaded by the same class loader as the PersistenceCapable class performing the registration.

Parameters:

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

fieldNames - an array of String field names.

fieldTypes - an array of Class field types

pc - the PersistenceCapable class.