Use Unsafe to set final static fields, support JDK12+

[eolivelli]

From JDK12+ is it no more possible to set a value to final static fields.
With this patch we are going to use Unsafe, that works on every JDK up to 13.
We are now also allowing to write to 'static final fields'

[thekingn0thing]

Test are falling

org.powermock.reflect.WhiteBoxTest > testSetInternalStateWithInvalidArgumentType FAILED
java.lang.Exception: Unexpected exception, expected<java.lang.IllegalArgumentException> but was<java.lang.RuntimeException>

    Caused by:
    java.lang.RuntimeException: java.lang.IllegalArgumentException: Can not set int field org.powermock.reflect.testclasses.ClassWithInternalState.internalState to java.lang.Object
        at org.powermock.reflect.internal.WhiteboxImpl.setFieldUsingUnsafe(WhiteboxImpl.java:2374)
        at org.powermock.reflect.internal.WhiteboxImpl.setField(WhiteboxImpl.java:2309)
        at org.powermock.reflect.internal.WhiteboxImpl.setInternalState(WhiteboxImpl.java:305)
        at org.powermock.reflect.Whitebox.setInternalState(Whitebox.java:174)
        at org.powermock.reflect.WhiteBoxTest.testSetInternalStateWithInvalidArgumentType(WhiteBoxTest.java:400)

        Caused by:
        java.lang.IllegalArgumentException: Can not set int field org.powermock.reflect.testclasses.ClassWithInternalState.internalState to java.lang.Object
            at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
            at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
            at sun.reflect.UnsafeIntegerFieldAccessorImpl.set(UnsafeIntegerFieldAccessorImpl.java:98)
            at java.lang.reflect.Field.set(Field.java:764)
            at org.powermock.reflect.internal.WhiteboxImpl.setFieldUsingUnsafe(WhiteboxImpl.java:2367)
            ... 4 more

org.powermock.reflect.WhiteBoxTest > testStaticFinalStringState FAILED
java.lang.AssertionError: Expected test to throw (an instance of java.lang.IllegalArgumentException and exception with message a string containing "You are trying to set a private static final String. Cannot set such fields!")

[eolivelli]

I will fix them.
Thank you for taking a look.

[eolivelli]

@thekingn0thing I have fixes the test.
PTAL

[eolivelli]

Hi @thekingn0thing
it would be great to have a release right after committing this fix, it will help a lot downstream projects that are migrating to jdk13/14 from jdk11

thanks

[thekingn0thing]

@eolivelli Merged. Thank you a lot for a pull request and sorry for such long delay.

[eolivelli]

@thekingn0thing thanks to you that you are maintaining this great project !

I hope we can get a release out soon, this patch brings back WhiteBox to full powers in modern jdks land

[thekingn0thing]

@eolivelli the library was automated released by pipline after the PR had been merged.
https://repo.maven.apache.org/maven2/org/powermock/powermock-api-mockito2/2.0.5/