Drools rules engine

Main method

KieContainer kc = KieServices.Factory.get().getKieClasspathContainer();

// load the DRL file; needs to be configured in kmodule.xml (see below)
KieSession ksession = kc.newKieSession("StudentAdvisorKS");

// insert some initial facts; perhaps you ask the user for these
Student johndoe = new Student("John", "Doe");
Course csci221 = new Course("Software Development I", "CSCI221", 4);
Course csci142 = new Course("XYZ", "CSCI142", 4);
CourseAttempt ca = new CourseAttempt(johndoe, csci142, new Semester("Fall", 2015), 3.5);

// fire all rules!

Metadata file

Required path: resources/META-INF/kmodule.xml

<?xml version="1.0" encoding="UTF-8"?>
<kmodule xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    <!-- change appropriately; "KB" and "KS" seem to be required? -->
    <kbase name="StudentAdvisorKB" packages="cc.artifice.csci431.studentadvisor">
        <ksession name="StudentAdvisorKS"/>

DRL (Rules) files

Example path: resources/cc/artifice/csci431/studentadvisor/StudentAdvisor.drl

Note, any classes used in the rules file need to have typical getters/setters.

DRL file


Besides rules, you can define queries to collect objects that satisfy certain conditions. Then, in your main Java code, you can (for example) get these objects into a list and do something with them (like print them).

DRL file:

query "people over the age of 30" 
    person : Person( age > 30 )

Java code:

System.out.println("These people are are over 30:");

QueryResults results = ksession.getQueryResults("people over the age of 30"); // parameter should match query name
for(QueryResultsRow row : results) {
    Person person = (Person)row.get("person");
    System.out.println(person.getName() + "\n");

Other rules engines

CSCI 431 material by Joshua Eckroth is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. Source code for this website available at GitHub.