creating a simple rule engine in java

Question

I am exploring different ways to create a simple business rule engine in Java. I need to present the client with a simple webapp that lets him configure a bunch of rules. A

Answer 1

Basically... Don't do it

To understand why see:

1. http://thedailywtf.com/Articles/The_Customer-Friendly_System.aspx
2. http://thedailywtf.com/Articles/The-Mythical-Business-Layer.aspx
3. http://thedailywtf.com/Articles/Soft_Coding.aspx

I know it looks like a great idea from afar, but the business rules engine will invariably end up being harder to maintain, deploy and debug then the programming language it was written in - don't make up your own programming languages if you can help it.

I've personally been down that road in an ex firm and I've seen where it goes after a couple years (giant undebuggable scripts sitting in a database written in a language that came straight from a parallel dimension where God hates us that in the end never meet 100% of customer expectation because they're not as powerful as a proper programming language and at the same time they're far too convoluted and evil for devs to handle (never mind the client)).

I know there's a certain kind of client that's enamoured with the idea that they won't pay programmer hours for "business rule adaptations" and little understand that they'll be worse off in the end and to attract this kind of client you'll have to make something in this direction - but whatever you do don't invent something of your own.

There's a plethora of decent scripting languages that come with good tools (that don't require compilation, so can be uploaded dynamically etc) out there that can be slickly interfaced and called from Java code and take advantage of your implemented Java apis that you make available, see http://www.slideshare.net/jazzman1980/j-ruby-injavapublic#btnNext for example, Jython possibly too,

and when the client gives up writing these scripts you will be left with the happy duty of maintaining his failed legacy - make sure that that legacy is as painless as it can be.