Using rpc.XserializeFinalFields

[Gerard Keiser]

I noticed there were many warnings about adding the experimental rpc.XserializeFinalFields flag (https://github.com/gwtproject/gwt/issues/1062). Is there anything I should be looking out for if I try this?

(Yes, I would prefer to just use Jackson, but that is a much larger migration effort.)

[Tim Macpherson]

I recently migrated from rpc to Domino Jackson. 

If your DTO classes are well formed it's not difficult - so far,  not completely tested 

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On Thu, Jul 10, 2025 at 2:54 PM, 'Gerard Keiser' via GWT Users

<google-we...@googlegroups.com> wrote:

I noticed there were many warnings about adding the experimental it's not rpc.XserializeFinalFields flag (https://github.com/gwtproject/gwt/issues/1062). Is there anything I should be looking out for if I try this?

(Yes, I would prefer to just use Jackson, but that is a much larger migration effort.)

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[Colin Alworth]

If your DTO classes care about specific collection implementations, or want maps with complex keys, or want to serialize non-tree graphs (so the same object can appear more than once when it gets to the client), JSON might add extra hurdles.

The final field serialization feature was added a long time ago, and I don't think I've seen any issues come up since it was first added.  Brian's comment near the end of that ticket still applies - it probably isn't safe to assume for general purpose libraries, but if you own the application as well, it should be safe to use.

[Tim Macpherson]

My DTOs had some circular references which were permissable for rpc but not for Jackson.

So far no other problems.

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.

[Gerard Keiser]

Thanks for the responses. The biggest thing, I suppose, is JPMS, especially since Java 17, which I have not yet had a need to learn much about. Am I setting myself up for reflection exceptions in unpredictable places, as suggested at https://docs.oracle.com/en/java/javase/17/migrate/migrating-jdk-8-later-jdk-releases.html#GUID-7BB28E4D-99B3-4078-BDC4-FC24180CE82B and https://github.com/gwtproject/gwt/issues/9793? If so, is there a good workaround? And after digging further, I found a proposal at https://openjdk.org/jeps/8349536 to disallow the final field modification used by the deserializer (https://github.com/gwtproject/gwt/blob/498c127d78e24e0768f50f16afdb0040e4317ea3/user/src/com/google/gwt/user/server/rpc/impl/ServerSerializationStreamReader.java#L851). So maybe this is a bad idea in the long-term unless the deserializer is able to be switched to using ReflectionFactory.

And unfortunately, the DTOs really are quite messy to use with Jackson.