问题
When upgrading to drools 5, valid drools 4 xml rules do not work. Drools just throws an unhelpful null pointer exception. What can the problem be?
回答1:
The problem is that Drools 5 changed the namespace. Replace xmlns="http://drools.org/drools-4.0" with xmlns="http://drools.org/drools-5.0" and at least for simple rules that is all you need.
I hope that helps save someone the headache I just got dealing with this undocumented change.
来源：https://stackoverflow.com/questions/3314292/i-just-upgraded-to-drools-5-and-the-xml-rules-will-not-load