[java][client] Fix regression in Java XML serialization

[bkabrda]

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• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
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CC @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04)

Description of the PR

Fixes regression reported in #4014.

@RockyMM since the current test cases don't cover this, could you try to grab this patch and verify that it fixes the regresssion? Thanks!

[RockyMM]

I have two points:

1. this change needs to be propagated to all pojo.mustache in other Java-based generators :( (I was expecting some inheritance, but seems it needs to be copied manually to JAX-RS, Spring and the likes)

2. this segment

   {{#jackson}}
   public static final String JSON_PROPERTY_{{nameInSnakeCase}} = "{{baseName}}";
   {{/jackson}}

also needs to be moved up.

[bkabrda]

So I moved the jackson's JSON_PROPERTY_* declaration as well, which should solve the second point. I honestly have no idea why this is a problem in all the other pojo templates, as I didn't touch them in my original PR that seemed to have caused this. Perhaps the issues with these were caused by different PRs?

[bkabrda]

I think the commit 1ab7b9c might have broken the other POJOs. I can try to fix that, but I'd prefer not mixing it with this PR, as the offending commits are different and this PR is for java clients.

[RockyMM]

Hm, in commit 1ab7b9c I checked the sample of Animal.java in "withXml" resttemplate example and it looked fine. So it might be that this is all the fix that we need.

It's interesting that when you've moved the jacksons JSON_PROPERTY_* that the generated samples also changed. I'm just getting a hold in this project so everything is new to me 😄

This means it is possible to write some automated tests for this so this won't appear again. Like check what is marshalled, and what is unmarsahlled and compare. I could help with this next week, but I think it is not really a show-stopper for the time being.

Update: I just saw #689 - I think it's very good idea. 👍

[wing328]

This means it is possible to write some automated tests for this so this won't appear again. Like check what is marshalled, and what is unmarsahlled and compare. I could help with this next week, but I think it is not really a show-stopper for the time being.

Yes, we welcome additional unit tests to ensure this issue won't happen again.

[wing328]

@RockyMM thanks for reviewing the fix.