JBoss Drools – Business Rules Management System/Guvnor

I was playing around with the web interface of the JBoss Drools engine called Business Rules Management System or BRMS till version 4.0.7. In the subsequent versions i.e 5.0 it is called Guvnor. While trying to validate the newly defined business rule, I got the following error:

java.lang.ClassFormatError: Incompatible magic value 1885430635 in class file

A quick search on the internet revealed the answer. Please ensure that your java class jar files contain only .class files and not source code. Weird yes, but that’s how it is!