[Java] Correct usage of fory-extensions

[ClaudioConsolmagno]

I can't find it documented anywhere but when do we want to use fory-extensions?

Since upgrading to version 0.10.3 (and have confirmed it's also happening in 0.11.0). I'm getting tons of log messages for protobuf coming from ProtobufDispatcher.java#L66

ProtobufSerializer not loaded, please add fury-extensions dependency.

Everything has been working fine so I'm not sure I'm constantly getting this log line. By adding the fory-extensions dependency or disabling logging for that class (e.g. logging.level.org.apache.fury.serializer.shim=ERROR) this warning goes away. But it feels that maybe this log line shouldn't be there in the first place?

[chaokunyang]

Yes, you are right, it should only be logged when we use fory to serializing protobuf classes. Would you like to create a PR to remove this ? But I think what needs being removed is

fory/java/fory-core/src/main/java/org/apache/fory/serializer/shim/ProtobufDispatcher.java

Line 56 in 5ebe5d2

LOG.warn("ProtobufSerializer not loaded, please add fory-extensions dependency.");

[ClaudioConsolmagno]

I think the log at line 56 is fine right? If it detects that protobuf.Message is in scope but ProtobufSerializer isn't, then this prints to log only once (since it's a static block). What needs to be removed is line 66.

Happy to make the PR.

[chaokunyang]

If users don't serialize any protobuf classe, fory shouldn't print such warning log. How about using a static variable to indicate whether we've already printed the warning logs, and print it only once when the first line 66 is executed.

[ClaudioConsolmagno]

Gotcha, I'll take a look. Any other places off the top of your head that you do something similar in the codebase I could use as example?

[chaokunyang]

Seems this is the first time we do such things, just take case to ensure thread safety for this static variable, other stuff should be OK

[ClaudioConsolmagno]

Have created this: #2353