OSGI + PAX CDI + Drools + Karaf

Drools

Drools is a powerful rule engine. You define rules using .drl file or .xls as an decision table

In this post we will see how Drool is embedded in Karaf as OSGI.

Pom.xml

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<groupId>com.frontend</groupId>

<artifactId>frontend-parent</artifactId>

</parent>

<artifactId>frontend-cmd2</artifactId>

<packaging>bundle</packaging>

<runtime.version>6.5.0.Final</runtime.version>

<cdi.version>1.1</cdi.version>

<weld.version>2.3.2.Final</weld.version>

</properties>

<version>${runtime.version}</version>

</dependency>

<groupId>org.drools</groupId>

<artifactId>drools-core</artifactId>

<version>${runtime.version}</version>

</dependency>

<groupId>org.drools</groupId>

<artifactId>drools-compiler</artifactId>

<version>${runtime.version}</version>

</dependency>

<groupId>org.drools</groupId>

<artifactId>drools-decisiontables</artifactId>

<version>${runtime.version}</version>

</dependency>

<groupId>javax.enterprise</groupId>

</dependency>

<groupId>org.jboss.weld.se</groupId>

<version>${weld.version}</version>

</dependency>

<version>${runtime.version}</version>

</dependency>

</dependencies>

</project>

Model Object

package org.drools.example.model;

public class Person {

private String name;

private String likes;

private String status;

private int age;

private boolean canDrink = false;

private boolean alive;

private char sex;

private boolean happy;

public Person() {

}

public Person(final String name) {

this( name,

"",

0 );

}

public Person(final String name,

final String likes) {

this( name,

likes,

0 );

}

public Person(final String name,

final String likes,

final int age) {

this.name = name;

this.likes = likes;

this.age = age;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public boolean isCanDrink() {

return canDrink;

}

public void setCanDrink(boolean canDrink) {

this.canDrink = canDrink;

}

public String getStatus() {

return this.status;

}

public void setStatus(final String status) {

this.status = status;

}

public String getLikes() {

return this.likes;

}

public boolean isAlive() {

return this.alive;

}

public void setAlive(final boolean alive) {

this.alive = alive;

}

public char getSex() {

return this.sex;

}

public void setSex(final char sex) {

this.sex = sex;

}

@Override

public String toString() {

return "Person{" + "name='" + name + '\'' + ", age=" + age

+ ", canDrink=" + canDrink + '}';

}

public boolean isHappy() {

return happy;

}

public void setHappy(boolean happy) {

this.happy = happy;

}

Helper Class

package org.drools.example.rule;

import org.drools.example.model.Person;

import java.util.Random;

public class PersonHelper {

private static final Random random = new Random();

public static Person createPerson() {

Person person = new Person();

if (random.nextBoolean()) {

person.setName("Old Person");

person.setAge(21);

} else {

person.setName("Young Person");

person.setAge(18);

}

return person;

}

public static void canDrink(Person aPerson) {

if (aPerson.isCanDrink()) {

System.out.println("Person " + aPerson.getName() + " aged of " + aPerson.getAge() + " , can go to the Bar");

} else {

System.out.println("Person " + aPerson.getName() + " aged of " + aPerson.getAge() + ", can't go to the Bar");

}

OSGI Class

It initializes the OSGI Service and Configure the KieSession

package org.drools.example.osgi;

import org.drools.example.model.Person;

import org.drools.example.rule.PersonHelper;

import org.kie.api.KieBase;

import org.kie.api.KieServices;

import org.kie.api.cdi.KSession;

import org.kie.api.runtime.KieContainer;

import org.kie.api.runtime.KieSession;

import org.ops4j.pax.cdi.api.ContainerInitialized;

import javax.annotation.PreDestroy;

import javax.enterprise.context.ApplicationScoped;

import javax.enterprise.event.Observes;

import javax.inject.Inject;

@ApplicationScoped

public class CanDrinkRuleOsgiCdiWeld {

/* @Inject

@KSession("sampleKSession")

KieSession ksession;*/

public void onStartup(@Observes ContainerInitialized event) {

KieServices ks = KieServices.Factory.get();

KieContainer kcont = ks.newKieClasspathContainer(getClass().getClassLoader());

KieBase kbase = kcont.getKieBase("sampleKBase");

KieSession ksession = kbase.newKieSession();

System.out.println("KieSession created.");

for (int i = 0; i < 20; i++) {

// Create a Person

Person aPerson = PersonHelper.createPerson();

ksession.insert(aPerson);

// Fire the rules

ksession.fireAllRules();

// Check if it can drink

PersonHelper.canDrink(aPerson);

}

@PreDestroy

public void onClose() {

System.out.println("KieSession disposed.");

}

The above class loads the xml file

kmodule.xml

SampleKBase loads the sampleKSession

<?xml version="1.0" encoding="UTF-8"?>

</kbase>

</kmodule>

which loads the DRL rule file below sample.drl

package org.drools.example.drink;

import org.drools.example.model.Person

rule "CanDrink"

when

p : Person( age >= 21 )

then

p.setCanDrink(true);

end

Initialize PAX-CDI we have to create an empty META-INF\beans.xml

Deploying in Karaf

Do mvn clean install

Karaf run the following commands

Install PAX-CDI & WELD

feature:install pax-cdi

feature:install pax-cdi-1.1-weld

Install the bundle

install -s mvn:com.frontend/frontend-cmd2/1.0