[DROOLS-1170] drools-pmml: use 'xjc' binary instead of jaxb2-maven-pl…

[psiroky]

…ugin

• jaxb2-maven-plugin is not yet supported on JDK9. The original
  idea was to create new profile which would be jdk9-specific
  and use the exec-maven-plugin only there. However, this does not
  work because the classes generated directly by 'xjc' and the
  plugin are not exactly the same. The one big difference is that
  the plugin useis 'is' prefix for Boolean properties whereas
  xjc will use 'get' prefix (e.g. public Boolean isAdult() vs
  public Boolean getAdult()). It seems the later is correct as
  'is' should only be used for primitive boolean, and not for object
  type Boolean (http://download.oracle.com/otndocs/jcp/7224-javabeans-1.01-fr-spec-oth-JSpec/).
  To make the configuration easier, the plugin was removed
  and the jxc is called directly.

The only thing I am wondering about is if it save to assume the xjc binary is on PATH? This may not always be the case. Maybe we should use ${env.JAVA_HOME}/bin/xjc instead?

@mariofusco, @ge0ffrey could you please take a look and let me know what you think?

[ge0ffrey]

I am not to found of these changes applying on a JDK 8 too.
I suspect that the maven-jaxb-plugin will be fixed some day in the future for JDK 9 at which time we 'll want to go back to the old method. Meanwhile it's indeed good to have a temporary workaround.

[psiroky]

@ge0ffrey sure I agree with that -- once the jaxb2-maven-plugin works both on JDK8 and JDK9, then we should use it again. But in the meantime I don't see other option here. If you know of better option please let me know, I would be more than happy to use it.

[ge0ffrey]

+1 to merge.
I am ok with this change - I don't know of a better option and we need to get the JDK9 builds running. I might add a comment TODO to state this is a temporary workaround until jaxb's normal goal supports it.

[psiroky]

I tweaked the TODO comment a bit. Hopefully it is a bit more clearer now.

[ge0ffrey]

+1 (I might have missed it the first time, sorry if I did)