Pros and cons of Java rules engines

brabster picture brabster · Jan 30, 2010 · Viewed 96.2k times · Source

What are the pros and cons to adopting the Java rules engines JESS and Drools? Are there any other players?

I understand that Drools is Open Source and JESS is not, but how do they compare in other areas like ease of use, performance, level of integration with your code?

Answer

Pascal Thivent picture Pascal Thivent · Jan 30, 2010

What are the pros and cons to adopting the Java rules engines JESS and Drools?

Use a rule engine if you need to separate the business rules from the application logic. The Does Your Project Need a Rule Engine article has a good example:

For example, a typical storefront system might involve code to calculate a discount:

if (product.quantity > 100 && product.quantity < 500) {
  product.discount = 2;
} else if (product.quantity >= 500 && product.quantity < 2000) {
  product.discount = 5;
} else if (product.quantity >= 2000) {
  product.discount = 10;
}

A rule engine replaces the above with code that looks like this:

ruleEngine.applyRules(product);

Up to you to decide whether putting a rule admin console in the hands of non-technical people is a good thing or not :)

More details in Should I use a Rules Engine?, Why use a Rule Engine?, Some Guidelines For Deciding Whether To Use A Rules Engine and on Google.

Are there any other players?

Other players include JRules, Corticon (JRules is the most famous IMO - which doesn't mean the best).

how do they compare in other areas like ease of use, performance, level of integration with your code?

Can't tell you precisely, I only have a little (positive) experience with Drools. But you'll get some feedback from blog posts like JBoss Drools vs ILog JRules - an anecdotal story (be sure to read it) or Working with Drools from a JRules perspective. I'm sure you can find more of them on Google (but I would give Drools a try).