It is not good to have all your business logic mixed with your code: in a web application, in a ETL process or inside your Java application. A more professional setup is to separate IT logic from business logic, as it also allows to separate the responsibilities properly: IT maintains the code and the business maintains the business logic.
This makes your IT code cleaner. And the business can concentrate on the business logic without being disturbed or confused by the IT logic around it. And that is also an important quality factor. If updates are required to the business logic, then the IT code does not need to be touched and it is the responsability of the business expert to maintain the rules and actions properly.
Having said this, you can include the ruleengine in your projects: Pentaho PDI, web application or a Java application and your business will benefit from it. The rules are maintained in the web application - ahndled by the business - and you can concentrate on the code. All you need to use the ruleengine in your Java code is a few lines of code. That's all.