Rule Engine in Java using Drools

This article will check some of the most popular rule engines in Java. Rule engine makes it easy to separate business logic from source code. We may view a rule engine as a sophisticated if/then statement interpreted by an expert system. In Java, most of the popular rule engines implement JSR94.

What is it?

It is an expert-system program that runs the rules on the data and if any condition matches, it executes the corresponding actions

This follows a basic approach; the “Human Expert defines the rule sets”. Then when the user requests any data/query, it goes to the rules engine interface, where it processes the request data and then gets the output/response from the ruleset files.

Types of Rule Engine in Java

In the Java world, most of the rule engines are written in Java and many of these rule engines follow the JSR94 standard. Here is the list of Rule Engine

• Drools-Drools is a Business Rule Management System (BRMS) solution. It provides a rule engine that processes facts and produces output due to rules and facts processing. The centralization of business logic makes it possible to make quick and cheap changes.
• OpenL tablets- OpenL Tablets is a business rules management system and a business rules engine based on Excel decision tables. Since the format of tables used by this framework is familiar to business users, it bridges the gap between business users and developers.
  
• Easy Rules- Easy Rules is a simple Java rules engine providing a lightweight and POJO-based framework to define the business. It can create complex rules from primitive ones by using the composite pattern.
• RuleBook- RuleBook is a Java framework that leverages Java 8 lambdas and the Chain of Responsibility Pattern to define rules using a simple BDD approach.

Find details here.

Java Configuration

Maven Dependency

<dependency>

<groupId>org.drools</groupId>

<artifactId>drools-decisiontables</artifactId>

<version>${drools-version}</version>

</dependency>

<dependency>

<groupId>org.drools</groupId>

<artifactId>drools-core</artifactId>

<version>${drools-version}</version>

</dependency>

<dependency>

<groupId>org.drools</groupId>

<artifactId>drools-compiler</artifactId>

<version>${drools-version}</version>

</dependency>

KieFileSystem- How does it work?

This is an in-memory file system provided by the framework, we set the path of the file to read and initialize.

KieContainer- How does it work?

Next, we need to set the KieContainer, a placeholder for all the KieBases for a particular KieModule. KieContainer is built with the help of other beans, including KieFileSystem, KieModule, and KieBuilder

KieSession- How does it work?

The rules are fired by opening a KieSession bean – which can be retrieved from KieContainer.

Read here