Lets learn Drools !!!: July 2015

Lets create a simple Drools example using Maven

Open Eclipse IDE
File -> New maven project
choose the simple maven project
enter the Group Id and Artifact Id as below

Group ID : com.droolstutorials.examples.drools
Artifact ID : Drools6.2Example

click Finish.

A pom.xml will be created in the project .
Add the below dependencies to it.

<dependencies>

<dependency>

<groupId>org.drools</groupId>

<artifactId>drools-compiler</artifactId>

<version>6.0.0.CR1</version>

</dependency>

<dependency>

<groupId>org.drools</groupId>

<artifactId>drools-core</artifactId>

<version>6.0.0.CR1</version>

</dependency>

</dependencies>

Your final pom.xml will look like this.

Lets create a Rule Executor file
Lets first create a package as below

src.main.java.com.droolstutorials.examples.drools.controller

and then create the java file as

RulesExecutor

RulesExecutor.java

package com.droolstutorials.examples.drools.controller;

import org.kie.api.KieServices;
import org.kie.api.builder.KieBuilder;
import org.kie.api.builder.KieFileSystem;
import org.kie.api.builder.KieRepository;
import org.kie.api.builder.Message.Level;
import org.kie.api.io.KieResources;
import org.kie.api.io.Resource;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;

public class RulesExecutor {
    public void runRules(String[] rules, Object[] employees) {
        KieServices kieServices = KieServices.Factory.get();
        KieResources kieResources = kieServices.getResources();
        KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
        KieRepository kieRepository = kieServices.getRepository();

        for (String ruleFile : rules) {
            Resource resource = kieResources.newClassPathResource(ruleFile);
            kieFileSystem.write(
                    "src/main/resources/com/droolstutorials/examples/drools/"
                            + ruleFile, resource);
        }

        KieBuilder kb = kieServices.newKieBuilder(kieFileSystem);
        kb.buildAll();

        if (kb.getResults().hasMessages(Level.ERROR)) {
            throw new RuntimeException("Build Errors:\n"
                    + kb.getResults().toString());
        }

        KieContainer kContainer = kieServices.newKieContainer(kieRepository
                .getDefaultReleaseId());

        KieSession kSession = kContainer.newKieSession();

        for (Object emp : employees) {
            kSession.insert(emp);
        }

        System.out.println("rules int "+kSession.fireAllRules());

    }
}

Lets now create a package as below

src.main.java.com.droolstutorials.examples.drools.model

and then create the java file (model) as

Employee

Employee.java

package com.droolstutorials.examples.drools.model;

public class Employee {
    private String name;
    private String type;

    public Employee(String name, String type) {
       this.name = name;
       this.type = type;
    }

    public String getName() {
       return name;
    }

    public void setName(String name) {
       this.name = name;
    }

    public String getType() {
       return type;
    }

    public void setAge(String type) {
       this.type = type;
    }

}

Lets now create a package as below

src.main.resources

and then create the .drl file as

Employee.drl

import com.droolstutorials.examples.drools.model.Employee

dialect "mvel"

rule "onsite"
    when
        $employee : Employee(type.equals("onsite"))
    then
        System.out.println("onsite :: "+$employee.name);
    end

rule "name without a"
   when
        $employee : Employee(!name.contains("a"))
    then
        System.out.println("name without a :: "+$employee.name);
   end

Now its time for creating the Main class to test it.

Create the main class in the below locaton

src.main.java.com.droolstutorials.examples.drools

Main.java

package com.droolstutorials.examples.drools;

import com.droolstutorials.examples.drools.controller.RulesExecutor;
import com.droolstutorials.examples.drools.model.Employee;

public class Main
{
    public static void main(String[] args)
    {
        RulesExecutor runner = new RulesExecutor();
        String valStr="";
        Employee naren = new Employee("Narendar", "onsite");
        Employee karthi = new Employee("KarthiK", "offshore");
        Employee ehfaj = new Employee("Ehfaj", "onsite");
        Employee bala = new Employee("Bala", "offshore");
        Employee pintu = new Employee("Pintu", "offshore");

        String[] rules = { "Employee.drl" };
        Object[] employees = {naren, karthi, ehfaj, bala, pintu};

        runner.runRules(rules,employees);
    }
}

Now run the Main as java application and you can see the drools rules getting executed.

Happy Drooling...

What basically is Drools..
Drools is an Object-Oriented Rule Engine for Java.
Its a rule based management framework, which takes care of giving you the output based on the condition you feed. simple right..

eg.,

Rule 1:
if you like this blog ?
read through

Rule 2:
if you dont like it?
you can Google drools :)

Basically what happens is like we give the input as
set of rules and
set of data
to the Drools engine. The Drools engine executes the rule (if.. then.. else) and gives the output as
Data Objects.

Rule is basically has a condition, if it becomes true, it initiates some actions.
Ok now lets write a bit technically valid rule and here it comes

rule "checkAmount"
when
$accountNumber : Account( money < 1000 )
then
AccountHolder.message($account.money);
end

Once the User has his balance less than 1000 bucks.. we are sending him an message.

Advantages of Drools are

they are flexible
reusable
easy to understand language unlike procedural languages.

http://www.drools.org/
will give the required jars and documentation.

Overall flow:

Facts : Data to be processed
Fact model : the model / pojo class written in java
Rule Engine : applies the rules from .drl files / excel sheet into the facts and gives the output.

Lets learn Drools !!!

Tuesday, July 28, 2015

Simple Drools using Maven

Drools Basics - Definitions

Drools Basics