Drools rulez?

Ok - I'm maybe the last in the universe to blog about Drools, the open source java business rule framework. I will not give another tutorial - but might help you avoid some traps :-)

• If you encounter "unsupported major.minor version 49.0", you might have included too many dependencies in your IDE. That error is known to occur when mixing 1.4 and 1.5 compiled classes.
• For Paul Brown's tutorial you only need a single drools jar in your dependencies - and that's drools-all-2.0.jar. Beware of including too many others, especially the annotation stuff :-(
  
• The Drools 2.1 maven build files are not out-of-the-box compatible with maven 1.1 - you have to manually remove the -tag from the build files.

Who the hell came up with the idea of formulating rules in XML style?
Otherwise drools is following a pretty cool concept - namely giving us kind'a framework for business logic. Alternatives exist, you may look at Jess, Ilog or YasuTech or others.