fix(#1156): illegal reflective access on java 9

[loicmathieu]

Hi,

This pull request allow to workaround the java 9 illegal access warning generated by mybatis.

When mybatis search for existing methods on objects, it goes to the object hierarchy including the top java.lang.Object class.

As there is no point to go to the java.lang.Object class as it didn't contains any getter/setter, a trivial workaround is to skip this class.
I tested this approach and with this patch there is no more illegall access warning on Java 9.

Regards,

Loïc

#1156

[harawata]

Thank you, @loicmathieu !

But, this is not the right fix.
Even after applied the patch, I see similar warnings when running BaseTest.

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.apache.ibatis.reflection.Reflector (file:/..../mybatis-3/target/classes/) to method java.lang.Class.checkPackageAccess(java.lang.SecurityManager,java.lang.ClassLoader,boolean)
WARNING: Please consider reporting this to the maintainers of org.apache.ibatis.reflection.Reflector
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

The real cause is the call to setAccessible() method, but simply removing the calls will break backward compatibility.
We haven't discussed this yet, but netty, for example, added a new option as a workaround.

[loicmathieu]

Hello,

Yes, my patch is not a correction of the issue but a workaround that works on my use case, when you only use mybatis on your own object with not private method (why is a setter or a getter private anyway), there is no issue as the setAccessible Method is not used.

I don't use mapper annotation, and apparently the illegall access warnings on BaseTest are due to the mapper annotation processing, I didn't have time to check this now. But if you launch the test with --illegal-access=warn with and without the patch you should see that the fixe corrected some warnings.

The netty way is to don't do setAccessible (this method should not have been used on the first place) on java 9 and allow to force it via a system property. This solution will break existing applications on Java 9 and they will be able to optin via a system property to works again.
Alternative is to use VarHandles but this is a hard path and will need to compile against java 9.

I agree that a more complete solution should be implemented, anyway, my fix will improve the situation as it will fix the issue in some cases (maybe a majority of cases) and it will also improve starting performance a little as it will avoid some reflection calls.

Regards,

Loïc

[harawata]

Well, the change itself is good as an optimization, but I'm not comfortable with treating this as a workaround for the warnings.
Would you consider removing the comment line?
Then I have no problem with merging this.

[loicmathieu]

Hello,
I remove the comment.
Regards,
Loïc

[harawata]

Thank you, @loicmathieu !