Re: java serialization alternative

On 2008.03.29., at 23:45, Bob Lee wrote:
> Making compatible changes isn't hard. Identifying incompatible
> changes, for example if a programmer makes a change to a class but
> forgets to consider serialization, is very tricky.

Oh yes, I completely agree with that.

> You simply can't
> verify compatibility statically with serialization.

Yep, one could actually append "... by definition" here, right? :-)

> The only way to
> verify that two classes are compatible is to run them and test them.
> You can either keep serialized data around in a file or something, or
> you can use a trick like this:
> http://crazybob.org/2006/01/unit-testing-serialization-evolution_13.html
> .
> Either approach is a pain in the butt.

Right - the real pain (which your blog entry doesn't show) is when
both classes are actually two versions of the same class, so you must
ensure you have both .class files available somewhere, have them
loaded through different class loaders, and then persuade the
ObjectInputStream to deserialize to the right class (as it's
notoriously ignorant of thread context class loader...). PITA indeed.

Although, alternatively, you could try reading ObjectStreamClass and
its ObjectStreamField objects from the stream and comparing them
against the in-memory class... oh well, actually you can't as if the
object has a custom writeObject/readObject, or is Externalizable, this
approach'd fail. (Just thinking out loud.)

>
>
> If you use a tool like Thrift, you can check two definitions for
> compatibility statically, so for example, you could add a submit check
> to your source control system or test suite to detect incompatible
> changes.

Nice - thanks for the pointer. I wonder how easy is it to extract this
functionality from Thrift, as otherwise it seems to be geared toward
RPC, and I'm more on the async messaging side of architecture...

Attila.

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