Drools presents us with several configuration options for its sessions—whether they are stateless or stateful. In this section, we are going to cover some of the options that we have in order to configure our sessions in a way that allows us to make full use of Drools' potential.

The most common way we usually interact with a Drools session is by inserting/modifying/retracting facts from it and executing any rule activation that may have happened as a consequence of these operations. All these operations target different aspects of the rule engine—such as knowledge assertion and inference—but there are also some other ways to interact with a session that can be used to provide or extract information to or from it. These operations are more oriented to the application where Drools is running and not to the rule engine itself. The options that we are going to review in this section are globals, channels, queries, and event listeners.