Integrating Easy Rules with a Spring Boot Microservice

This post will walk you through integrating the lightweight and straightforward Easy Rules engine with your Spring Boot microservice. We’ll cover the necessary dependencies, basic setup, and an example service to demonstrate its usage.

1. Project Setup and Dependencies

Start by creating a Spring Boot project. Next, add the following Easy Rules dependencies to your pom.xml (Maven) or build.gradle (Gradle) file:

Maven:

XML

<dependency>
    <groupId>org.jeasy</groupId>
    <artifactId>easy-rules-core</artifactId>
    <version>5.3.0</version>
</dependency>

Gradle:

Gradle

implementation 'org.jeasy:easy-rules-core:5.3.0'

2. Defining Rules with Easy Rules

Easy Rules promotes a POJO-based approach for defining rules. Create a class that implements the org.jeasy.rules.api.Rule interface:

Java

import org.jeasy.rules.annotation.Action;
import org.jeasy.rules.annotation.Condition;
import org.jeasy.rules.annotation.Rule;

@Rule(name = "Discount Rule", description = "Apply 10% discount for orders over $100")
public class DiscountRule {

    @Condition
    public boolean isApplicable(Order order) {
        return order.getTotalPrice() > 100;
    }

    @Action
    public void applyDiscount(Order order) {
        order.applyDiscount(0.1);
    }
}

This code defines a rule named “Discount Rule”. The isApplicable method defines the condition (order total price greater than 100), and the applyDiscount method defines the action (apply a 10% discount).

3. Using Easy Rules in a Service

Inject the RulesEngine bean into your service class and use it to fire rules against your domain objects.

Java

import org.jeasy.rules.api.RulesEngine;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.Arrays;

@Service
public class OrderService {

    @Autowired
    private RulesEngine rulesEngine;

    public Order applyRules(Order order) {
        rulesEngine.fire(Arrays.asList(new DiscountRule()), Arrays.asList(order));
        return order;
    }
}

This service:

• Injects the RulesEngine bean.
• Creates an instance of the DiscountRule.
• Fires the rule against the provided order object.
• Returns the modified order object.

4. Configuration Setup

Easy Rules has sensible defaults and often requires minimal configuration. You can customize the RulesEngine by defining your own bean:

Java

import org.jeasy.rules.api.RulesEngineParameters;
import org.jeasy.rules.core.DefaultRulesEngine;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class EasyRulesConfig {

    @Bean
    public RulesEngine rulesEngine() {
        RulesEngineParameters parameters = new RulesEngineParameters()
                .skipOnFirstAppliedRule(true); // Example parameter
        return new DefaultRulesEngine(parameters);
    }
}

5. YML Changes (Not Required)

Easy Rules doesn’t typically require specific configuration in your application.yml or application.properties file.

This guide provides a basic introduction to integrating Easy Rules with your Spring Boot microservice. Its simplicity and annotation-based approach make it easy to define and manage business rules. You can expand on this by exploring more advanced features like rule composition, priority, and custom rule listeners. Remember to tailor the rules and domain models to your specific business needs.