HHH-12295 Restore compatibility with Java 6 on branch 5.1

[Sanne]

https://hibernate.atlassian.net/browse/HHH-12295

N.B. this PR is for branch 5.1 only.

[Sanne]

@vladmihalcea , could you have a look please? I removed the Pattern.UNICODE_CHARACTER_CLASS flag in your regex but I'm not sure I understand the implications.

Pattern.UNICODE_CHARACTER_CLASS is not available in Java 6, while ORM 5.1 should still be compatible with Java 6, so this flag has to go. Maybe we need a different replacement?

[vladmihalcea]

@Sanne I remember that I added the UNICODE_CHARACTER_CLASS after someone complained that his Java Constants written with Chinese Glyphs were not caught by that Regex.

If all tests pass just fine ReflectHelperTest#test_getConstantValue_constant_digits passes just fine, then no worries.

[Sanne]

thanks Vlad. I'll merge this then.

[Sanne]

ah no.. forgot this is 5.1.

I'll let Gail merge it so she can check it all.

[Sanne]

@gbadner ? I thought this was urgent, and should be trivial to check. Just looking for your ACK.

[gbadner]

@Sanne , ReflectHelperTest#test_getConstantValue_constant_digits is failing.

@vladmihalcea , any suggestions?

[rstancel]

@gbadner the issue here is that the pattern is requiring class with 2 uppercase letters and the test class contains only one. So the solution can be to update test data. Something like that: rstancel@f0806b6

[gbadner]

@rstancel, IIUC, you've just change the test code. The bug remains.

[rstancel]

@gbadner I don't understand. Sanne has fixed the issue itself but his fix was failing one test. So I took his fix and added also a fix for this test. Is there something else which should be fixed?

[gbadner]

@rstancel, the problem is that the proposed fix to ReflectHelper will introduce a regression into 5.1 branch. Fixing the test to pass does not fix the regression.

It turns out that upgrading dom4j to 2.2.1 (HHH-12964) requires JDK8 in 5.1.17 anyhow, so it will not be possible to restore compatibility with JDK6 in 5.1.