org.eclipse.persistence.sdo

Class SDOResolvable

java.lang.Object

org.eclipse.persistence.sdo.SDOResolvable

All Implemented Interfaces:

ExternalizableDelegator.Resolvable, java.io.Externalizable, java.io.Serializable

public class SDOResolvable
extends java.lang.Object
implements ExternalizableDelegator.Resolvable

INTERNAL:

Purpose:

This class performs serialization/deserialization of an SDODataObject.

Responsibilities:

• Provide/override default Java serializable access to a DataObject

Serialization Process

Serialization and de-serialization of objects occurs during DAS transactions, Web Service transactions in the SOAP envelope, EJB container passivation, web container session saving or directly in an application using the function ObjectOutputStream.writeObject(Object). The Serializable and Externalizable framework handles automatic or user defined reading/writing of streams depending on which interface functions are realized in the implementing classes.

The Serializable interface has no operations - therefore a class that implements it needs to add no additional functionality. Why do this? - For security. The security manager in the JVM will only serialize objects at runtime if they are flagged as Serializable (or Externalizable) so that by default java classes do not expose themselves to serialization. (See p49 of Java Security 2nd edition).

There are 3 levels of serialization control.

• 1) Default Serialization
  
Here we make the class implement Serializable, mark non-serializable fields as transient and implement no new functions.
• 2) Partial custom Serialization
  
Here we make the class implement Serializable and implement the optional functions writeObject and readObject to handle custom serialization of the current class while using the default serialization for super and subtypes.
• 3) Fully customized Serialization - current implementation.

Here we make the class implement Externalizable and implement the functions readResolve, writeReplace, readExternal, writeExternal. Supertypes and subtypes must also implement these functions.

The SDO 2.01 specification details the high level structure of the serialization format on page 64, section 6 - Java Serialization of DataObjects. The process will involve gzip serialization of the xml data with UTF representation of the Xpath address of the current DataObject inside the entire tree along with its identification as root/no-root in binary 1/0 format as follows.

• Security:

The following public functions expose a data replacement vulnerability where an outside client can gain access and modify their constants. We may need to wrap the GZIP streams in some sort of encryption when we are not using HTTPS or SSL/TLS on the wire. public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException public void writeExternal(ObjectOutput out) throws IOException
• Concurrency:

Avoid synchronized classes that will queue threaded clients such as Enumeration, Vector etc. We need to discuss how this API will be used by containers like an EJB container that can invoke multithreaded clients.
• Scalability:


• XML Serialization Size is 4GB:

There is a limitation set by the SDO Specification on the size of the DataObject serialization. According to the spec we must use an integer to define the size of the GZIP buffer that is serialized. This size is limited to +/- 2GB. This limitation is actually set by the JVM itself because a call to buffer.length returns a signed 32 bit integer.
• Performance:

Using custom serialization via the Externalizable interface is 30% faster than the default java serialization because the JVM does not need to discover the class definition.

See Also:

Serialized Form

Since:

Oracle TopLink 11.1.1.0.0

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	DEFAULT_ROOT_ELEMENT_NAME Root element name for all DataObjects undergoing serialization = sdo:dataObject
static int	SDO_HELPER_CONTEXT_ID_IDENTIFIER root object with helper context id identifier
static int	SDO_INTERNAL_OBJECT_IDENTIFIER internal object serialization type identifier = 0
static int	SDO_ROOT_OBJECT_IDENTIFIER root object serialization type identifier = 1

Constructor Summary

Constructors

Constructor and Description
SDOResolvable()
SDOResolvable(HelperContext aContext) Default constructor for deserialization
SDOResolvable(java.lang.Object target, HelperContext aContext) Constructor for serialization

Method Summary

Methods

Modifier and Type	Method and Description
HelperContext	getHelperContext()
void	readExternal(java.io.ObjectInput objectInput) Purpose: Deserialize from an ObjectInputStream into an SDODataObject This function is mandated by the Externalizable interface.
java.lang.Object	readResolve() Purpose: This function is called after readExternal to return the recently deserialized object retrieved from the ObjectInputStream.
void	setHelperContext(HelperContext helperContext)
void	writeExternal(java.io.ObjectOutput objectOutput) Purpose: Serialize an SDODataObject to an ObjectOutputStream This function is mandated by the Externalizable interface.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_ROOT_ELEMENT_NAME

public static final java.lang.String DEFAULT_ROOT_ELEMENT_NAME

Root element name for all DataObjects undergoing serialization = sdo:dataObject

See Also:

Constant Field Values

SDO_HELPER_CONTEXT_ID_IDENTIFIER

public static final int SDO_HELPER_CONTEXT_ID_IDENTIFIER

root object with helper context id identifier

See Also:

Constant Field Values

SDO_ROOT_OBJECT_IDENTIFIER

public static final int SDO_ROOT_OBJECT_IDENTIFIER

root object serialization type identifier = 1

See Also:

Constant Field Values

SDO_INTERNAL_OBJECT_IDENTIFIER

public static final int SDO_INTERNAL_OBJECT_IDENTIFIER

internal object serialization type identifier = 0

See Also:

Constant Field Values

Constructor Detail

SDOResolvable

public SDOResolvable()

SDOResolvable

public SDOResolvable(HelperContext aContext)

Default constructor for deserialization

SDOResolvable

public SDOResolvable(java.lang.Object target,
             HelperContext aContext)

Constructor for serialization

Method Detail

readResolve

public java.lang.Object readResolve()
                             throws java.io.ObjectStreamException

Purpose: This function is called after readExternal to return the recently deserialized object retrieved from the ObjectInputStream. Here there is an opportunity to replace the object with a Singleton version

Specified by:

readResolve in interface ExternalizableDelegator.Resolvable

Throws:

java.io.ObjectStreamException

writeExternal

public void writeExternal(java.io.ObjectOutput objectOutput)
                   throws java.io.IOException

Purpose: Serialize an SDODataObject to an ObjectOutputStream This function is mandated by the Externalizable interface. It writes binary data in the same order as was will be read back in readExternal(). Prerequisites: An object has already been constructed and associated with the theSDODataObject member

Specified by:

writeExternal in interface java.io.Externalizable

Throws:

java.io.IOException

readExternal

public void readExternal(java.io.ObjectInput objectInput)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException

Purpose: Deserialize from an ObjectInputStream into an SDODataObject This function is mandated by the Externalizable interface. It reads back binary data in the same order as was written in writeExternal(). An object has already been constructed with the no-arg constructor before this function fills in the member fields. The deserialized object will be returned later in a call from the ObjectInputStream to readResolve()

Specified by:

readExternal in interface java.io.Externalizable

Throws:

java.io.IOException

java.lang.ClassNotFoundException

getHelperContext

public HelperContext getHelperContext()

Returns:

setHelperContext

public void setHelperContext(HelperContext helperContext)

Parameters:

helperContext -