{"id":90780,"date":"2019-04-17T10:00:51","date_gmt":"2019-04-17T07:00:51","guid":{"rendered":"https:\/\/www.javacodegeeks.com\/?p=90780"},"modified":"2019-04-16T10:56:31","modified_gmt":"2019-04-16T07:56:31","slug":"a-complete-tutorial-on-the-drools-business-rule-engine","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2019\/04\/a-complete-tutorial-on-the-drools-business-rule-engine.html","title":{"rendered":"A complete tutorial on the Drools business rule engine"},"content":{"rendered":"

As always we share the code presented in the tutorial in a companion repository: EmailSchedulingRules<\/a>.<\/p>\n

Business rules work very well to represent the logic for certain domains. They work well because they result intuitive and close to the way of thinking of many types of domain experts<\/strong>. The reason for that it is that they permit to decompose a large problem in single components. In this way the user has not to deal with the orchestration of all the single rules: this is the added value provided by the business rule engine.<\/p>\n

In this article we will discuss one specific example of application written by using business rules. We will write the rules to decide which email to send to the subscribers to a newsletter. We will see different types of rules and how we could express them using the Drools Rule Language. We will also see how to configure Drools<\/a> (spoiler: it will be easy) and have the system elaborate the rules to produce a result we can use.<\/p>\n

I think that business rules are quite interesting because they permit to look at problems in a different way. As developers we are very used to the imperative paradigm or functional paradigms. However there are other paradigms, like state machines and business rules, which are not so commonly used and which can be a much better fit in some contexts.<\/p>\n

As always we share the code presented in the tutorial in a companion repository: EmailSchedulingRules<\/a>.<\/em><\/p>\n

What problem we are trying to solve<\/h2>\n

Let\u2019s consider the domain of email marketing. As marketers we have an email list of persons interested in our content. Each of them may have demonstrate interest in a specific topic, read some of our articles and bought certain products. Considering all their history and preferences we want to send to them at each time the most appropriate content. This content may be either educative or proposing some deal. The problem is that there are constraints we want to consider (i.e., not sending emails on sunday or not sending emails promoting a product to someone who already bought it).<\/p>\n

All these rules are simple per se, but the complexity derives by how they are combined and how they interact. The business rule engine will deal with that complexity for us, all we have to do is to express clearly the single rules. Rules will be expressed in the terms of our domain data so let\u2019s focus on our domain model first.<\/p>\n

The model of our domain<\/h3>\n

In our domain model we have:<\/p>\n