Avoid unnecessary setAccessible() calls.

[harawata]

As a fix for #1156 .

I used retry-on-failure approach as isAccessible() is useless (always returns false on the first call).
It would be appreciated if someone can test this with named modules.

[dawwin]

I have tested your changes on JDK10 (without named modules) and looks like this change solves problem with "Illegal reflective access" warnings. I'll try to test it with named modules if I find time to do it :).

I have one question though. You have moved calls to setAccessible() to Invoker implementations. Isn't it now possible to concurrently call setAccessible() on the same Field object from different threads?

[harawata]

@dawwin ,

Thank you very much for testing!

Regarding setAccessible(), it is indeed possible that multiple threads call the method concurrently.
As those Invokers always pass true to setAccessible(), I think it's fine, but please let me know in case I am missing something.

[dawwin]

I did some tests with modules and it seems that this change works fine with JDK10. Here is the example app I used for testing: https://github.com/dawwin/mybatis.jdk10test .
Model classes have to be exported to mybatis if all classes/getters/setters are public. If there are some not public fields - for example setters, then opens has to be used, otherwise it will fail (See module-info.java in repository I mentioned). So it seems to be ok.

I found one unrelated issue with JDK10, but I will report it separately

[harawata]

Hi @dawwin ,
Thank you so much for the example app! I haven't had time to try it yet, but I sure will.
The behavior you described matches my expectation, so this seems to be the right approach. :)

[harawata]

I am going to merge this so that users can test it with snapshot.
I'll revert it if there is any unfixable issue.