1.1 Overview

The ability to store and retrieve Java^TM objects is essential to building all but the most transient applications. The key to storing and retrieving objects in a serialized form is representing the state of objects sufficient to reconstruct the object(s). Objects to be saved in the stream may support either the Serializable or the Externalizable interface. For Java^TM objects, the serialized form must be able to identify and verify the Java^TM class from which the contents of the object were saved and to restore the contents to a new instance. For serializable objects, the stream includes sufficient information to restore the fields in the stream to a compatible version of the class. For Externalizable objects, the class is solely responsible for the external format of its contents.

Objects to be stored and retrieved frequently refer to other objects. Those other objects must be stored and retrieved at the same time to maintain the relationships between the objects. When an object is stored, all of the objects that are reachable from that object are stored as well.

The goals for serializing Java^TM objects are to:

• Have a simple yet extensible mechanism.
• Maintain the Java^TM object type and safety properties in the serialized form.
• Be extensible to support marshaling and unmarshaling as needed for remote objects.
• Be extensible to support simple persistence of Java^TM objects.
• Require per class implementation only for customization.
• Allow the object to define its external format.