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6.2 Stream Elements

A basic structure is needed to represent objects in a stream. Each attribute of the object needs to be represented: its classes, its fields, and data written and later read by class-specific methods. The representation of objects in the stream can be described with a grammar. There are special representations for null objects, new objects, classes, arrays, strings, and back references to any object already in the stream. Each object written to the stream is assigned a handle that is used to refer back to the object. Handles are assigned sequentially starting from 0x7E0000. The handles restart at 0x7E0000 when the stream is reset.

A class object is represented by the following:

An ObjectStreamClass object for a Class that is not a dynamic proxy class is represented by the following:

An ObjectStreamClass object for a dynamic proxy class is represented by the following:

The representation of String objects depends on the length of the UTF encoded string. If the UTF encoding of the given String is less than 65536 bytes in length, the String is written in the standard Java UTF-8 format. Starting with the JavaTM 2 SDK, Standard Edition, v1.3, strings for which the UTF encoding length is greater than or equal to 65536 bytes are written in a variant "long" UTF format. The "long" UTF format is identical to the standard Java UTF-8 format, except that it uses 8 bytes to write the length of the UTF string, instead of 2 bytes. The typecode preceding the String in the serialization stream indicates which format was used to write the String.

Arrays are represented by the following:

New objects in the stream are represented by the following:

All primitive data written by classes is buffered and wrapped in block-data records, regardless if the data is written to the stream within a writeObject method or written directly to the stream from outside a writeObject method. This data can only be read by the corresponding readObject methods or be read directly from the stream. Objects written by the writeObject method terminate any previous block-data record and are written either as regular objects or null or back references, as appropriate. The block-data records allow error recovery to discard any optional data. When called from within a class, the stream can discard any data or objects until the endBlockData.



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