final transient fields serialization
David Holmes - Sun Microsystems
David.Holmes at Sun.COM
Mon Nov 9 15:54:50 PST 2009
Pawel Veselov said the following on 11/10/09 07:30:
> it again caught my attention, and I though that may be there is
> something that can be done about this.
> The issue is obvious -- having 'final transient' instance fields makes
> little sense if the object is ever serialized.
> Logically, there may be perfect reasoning behind making an instance
> field final, as well as transient, in which case there is then no
> mechanism to reinitialize this field on object deserialization.
Not quite true. This problem - that final fields can only be set during
true construction and not during the pseudo-construction that occurs
during deserialization - has been realized for a long time. As part of
the Java 5 update we (I think it was done JSR-133) put in place the
mechanism whereby you can use reflection to set a final field provided
that setAccessible(true) has been invoked for that field. This is of
course a limited solution as you must have the security capability to
JSR-133 also addresses the Java Memory Model issues concerning
deserialization of objects with final fields - see Section 17.5.3 of the
Java Language Specification. (The notion of a "freeze action" on a final
field was in part motivated by the deserialization issue).
> It seems that it would be nice if either the final fields were
> initialized in a separate block that would be executed on
> deserialization, or if readObject() could set them. After all you can
> have a code block that sets the final fields. Not sure how feasible that
> is, but IMHO, that is a short coming.
> With best of best regards
> Pawel S. Veselov
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