Since the topic of serialization has come up recently, I'll take it as
an excuse to bring up a problem that I've run into a couple of times
with the serialization specification, which has resulted in user problems.
If you read section 2.3 [1] of the specification, it says:
"The class's writeObject method, if implemented, is responsible for
saving the state of the class. Either ObjectOutputStream's
defaultWriteObject or writeFields method must be called once (and only
once) before writing any optional data that will be needed by the
corresponding readObject method to restore the state of the object; even
if no optional data is written, defaultWriteObject or writeFields must
still be invoked once. If defaultWriteObject or writeFields is not
invoked once prior to the writing of optional data (if any), then the
behavior of instance deserialization is undefined in cases where the
ObjectInputStream cannot resolve the class which defined the writeObject
method in question."
If you go to section 3.4 [2] of the specification, it reads:
"The readObject method of the class, if implemented, is responsible for
restoring the state of the class. The values of every field of the
object whether transient or not, static or not are set to the default
value for the fields type. Either ObjectInputStream's defaultReadObject
or readFields method must be called once (and only once) before reading
any optional data written by the corresponding writeObject method; even
if no optional data is read, defaultReadObject or readFields must still
be invoked once."
Now the problem: there are many classes in the wild which nevertheless
do not write/read fields. We cause an exception in such cases rather
than make up some undefined behavior. What I'm wondering is, is there
some sensible behavior that could be specified for this case? The
Oracle JDK seems to simply leave fields uninitialized in this case,
maybe that can be a specified behavior?
[1]
http://docs.oracle.com/javase/7/docs/platform/serialization/spec/output.html#861
[2]
http://docs.oracle.com/javase/7/docs/platform/serialization/spec/input.html#2971
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- DML
