3 Step Tutorials

1. Introduction to Drools
2. Environment Setup
3. Programming with Drools

Lets start with a basic but complete program to get a Drools project up and running.

Program

For our first program, we will have the following files
A POJO class with getters and setters
A Java class for executing the application
A Rule file (with.drl extension)

Customer.java

package com.drools.examples;

public class Customer {

    private Account account;
    private String name;

    public String getName() {
        return name;
    }

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

    public Account getAccount() {
        return account;
    }

    public void setAccount(Account account) {
        this.account = account;
    }
}

Account.java

package com.drools.examples;

public class Account {

    private double balance;
    private int acct_no;

    public Account(int acct_no)
    {
        this.acct_no = acct_no;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }

    public int getAcct_no() {
        return acct_no;
    }
}

BankApp.java

package com.drools.examples;

import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.io.ResourceFactory;
import org.drools.runtime.StatefulKnowledgeSession;

public class BankApp {

    public static final void main(String[] args) {
    KnowledgeBase knowledgeBase = createKnowledgeBase();
    StatefulKnowledgeSession session = knowledgeBase
    .newStatefulKnowledgeSession();
    try {
    Customer customer1 = new Customer();
    Account account1 = new Account(100001);
    account1.setBalance(100);
    customer1.setAccount(account1);
    customer1.setName("George");

    Customer customer2 = new Customer();
    Account account2 = new Account(100002);
    account2.setBalance(5000);
    customer2.setAccount(account1);
    customer2.setName("Jim");

    Customer customer3 = new Customer();
    Account account3 = new Account(100003);
    account3.setBalance(220);
    customer3.setAccount(account3);
    customer3.setName("Harry");

    session.insert(account1);
    session.insert(account2);
    session.insert(account3);
    session.fireAllRules();
    }
    finally {
    session.dispose();
    }
    }

    private static KnowledgeBase createKnowledgeBase() {
    KnowledgeBuilder builder = KnowledgeBuilderFactory
    .newKnowledgeBuilder();
    builder.add(ResourceFactory
    .newClassPathResource("bank.drl"),
    ResourceType.DRL);
    if (builder.hasErrors()) {
    throw new RuntimeException(builder.getErrors()
    .toString());
    }
    KnowledgeBase knowledgeBase = KnowledgeBaseFactory
    .newKnowledgeBase();
    knowledgeBase.addKnowledgePackages(builder
    .getKnowledgePackages());
    return knowledgeBase;
        }
    }

bank.drl

package com.drools.examples

//list any import classes here.

//declare any global variables here

rule "Low Balance Rule"

    when
        $account:Account($bal:balance<250)
    then
        System.out.println("Rule fired:The following account has low balance(<$250):"+"Account#:"+$account.getAcct_no()+", Available balance:"+$account.getBalance());

end

3 Step Tutorials

Pages

Friday 16 August 2013

Programming with Drools