How Does the Rule Engine work?

Step 1: Set Up Your Java Project

To set up a Java project, you need to create a new Java project or can also use an existing project. Before you can implement rule engines in your Java project, you have to ready a Java project with required configured settings in your Java project. If you don’t have an existing Java project then you can also follow these steps to create the new one.

Open your Integrated Development Environment (IDE).
Create a new project.
Configure project settings by ensuring the appropriate Java version for your project.
Create a package in your ‘src’ folder.
Create a Class which can be denoted by any name like ‘Main’ or ‘RuleEngineExample’, and serves as an entry point for the project.
Write a simple Java code snippet.
Save and Build.

Step 2: Add Rule Engine tools dependencies in your pom.xml file or yml file.

For Example, adding dependency for Drools engine in your xml file, if you are using Maven.

XML

<dependencies> 
    <dependency> 
        <groupId>org.drools</groupId> 
        <artifactId>drools-core</artifactId> 
        <version>7.65.0.Final</version> <!-- Use the latest version available -->
    </dependency> 
</dependencies>

Step 3: Create a Fact class

The Fact class which refers to the class that represents the data or facts upon which the rules will be applied, in the following example the ‘Person’ class is considered a Fact Class. Generally in the rule engine, especially in the case of Drools rule engine, the class.java is replaced with the fact class and normally represented as a class.java or person.java.

Java

// Person.java 
public class Person { 
    private String name; 
    private int age; 
    private boolean eligibleForDiscount; 
    private boolean specialStatus; 
  
    // Your Getters and setters 
}

Step 4: Write a Rule in your Java project

Here we are creating a rule file for the Drools rule engine named ‘GeeksRule.drl’, where ‘drl’ is the extension for the Drools rule.

Java

// GeeksRule.drl 
rule "w3wiki Rule"
    when 
        $person: Person(age < 30, name.contains("w3wiki")) 
    then 
        $person.setSpecialStatus(true); 
end

‘w3wiki’ rule is the name assigned to this rule, it serves as a label for identification and readability and the ‘end’ mark is represented as the end of that particular rule. This rule states that if a person’s age is less than 30 and their name contains “w3wiki”, they are granted a special status.

Step 5: Use Drools in Your Java Code

Create a Java class to use Drools to evaluate the w3wiki rule.

Java

import org.kie.api.*; 
import org.kie.api.runtime.*; 
  
public class RuleEngineExample { 
    public static void main(String[] args) { 
        KieServices kieServices = KieServices.Factory.get(); 
        KieContainer kieContainer = kieServices.getKieClasspathContainer(); 
        KieBase kieBase = kieContainer.getKieBase(); 
        KieSession kieSession = kieBase.newKieSession(); 
  
        Person person = new Person("w3wiki User", 25); 
        kieSession.insert(person); 
  
        int ruleFiredCount = kieSession.fireAllRules(); 
  
        System.out.println("Rules fired: " + ruleFiredCount); 
        System.out.println("Is person eligible for a special status? " + person.isSpecialStatus()); 
  
        kieSession.dispose(); 
    } 
} 

Step 6: Run your Java project

Run your Java project, and you should see output indicating whether the w3wiki rule was fired and whether the person is eligible for a special status based on the provided name and age. The above example demonstrates how you can use Drools to apply rules related to w3wiki within a Java project. Adjust the rule and data objects as needed for your specific use case.

Rule Engines in Java

Rule engines in Java provide us with a framework for managing and performing business rules in a flexible and defining manner. These engines allow the developers to separate the business logic from the application code by making it easier to modify and understand rules without changing the core application.

Rule engines are designed to evaluate the conditions and trigger the actions based on specified rules. They also provide us with a more dynamic and adaptable approach to handling complex decision-making processes. This article introduces various rule engines that allow developers to automate their software application logic. By integrating these rule engines, developers can significantly contribute to the automation of business policies, ultimately resulting in more robust and effective software applications.