| A stream for serializing objects with format id tags.
An ObjectOutput (henceforth 'out') preceeds objects it writes with
a format id. The companion FormatIdInputStream (henceforth 'in')
uses these format ids in parsing the stored data. The stream
can be thought of as containing a sequence of (formatId,object) pairs
interspersed with other data. The assumption is that out.writeObject()
produces these pairs and in.readObject() uses the format ids to
construct objects from the pairs that out.writeObject produced.
The description below describes each supported pair and how in.readObject()
processes it.
- (NULL_FORMAT_ID, nothing) in.readObject() returns null.
- (SRING_FORMAT_ID, UTF8 encoded string)in.readObject reads and
returns this string.
- (SERIALIZABLE_FORMAT_ID,serialized object) in.readObject() reads
the object using java serialization and returns it.
- (A format id for a Storable, isNull flag and object if isNull == false)
(see note 1) in.readObject() reads the boolean isNull flag. If is null
is true, in.readObject() returns a Storable object of the correct
class which is null. If ifNull is false, in.readObject() restores
the object using its readExternal() method.
- (A format id for a Formatable which is not Storable, the stored object)
(see note 1) in.readObject restores the object using its
readExternal() method.
Note 1: The FormatIdInputStream uses
Monitor.newInstanceFromIdentifier(format id) to get the class.
Note 2: An object may support more than one of the following
interfaces Storable, Formatable, Serializable. In this case out.writeObject
use the first of these interfaces which the object supports (based on the order
listed here) to determine how to write the object.
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