Popular Rule Engines in Java
1. Drools
Drools rule engine is widely known as the ‘Business Rules Management System’ (BRMS) which is widely used as an open-source rule engine for Java, it helps in encouraging the developers to implement and manage the such complex business logics.With exclusive functionalities, Drools is the preferred choice of the Java developers for rule based software applications in the diverse domains.
Example:
Java
// Define a rule rule "Example Rule" when $fact: SomeObject(property > 10) then // Actions to be executed when the rule is matched $fact.setFlag(true); end |
2. Jess
Jess is a rule engine which is designed for the Java platform, and frequently used in Java applications while developing the expert systems. Its user-friendly scripting language and robust reasoning engine make it well suited for the complex decision making, and helps in establishing it as a valuable choice for such tasks which requires the advanced rule based systems in the Java applications.
Example:
Java
// Define a rule (defrule example-rule (some-object (property > 10)) => (modify some-object (set-flag true))) |
3. Easy Rules
Easy Rules, recognized as a lightweight and straightforward rule engine for Java, stands out in providing rule abstraction for creating the rules based on defined actions and conditions. Its simplicity and flexibility make it a preferred choice for developers seeking an uncomplicated yet effective solution for implementing and managing the rules in Java applications, and facilitating a seamless integration of business logic in the application.
Example:
Java
// Define a rule Rule someRule = new BasicRuleBuilder() .name("Example Rule") .when(facts -> facts.get("property", Integer.class) > 10) .then(facts -> facts.put("flag", true)) .build(); |
4. Rule Book
Rule Book offers a user-friendly and flexible DSL which makes its rule creation straightforward. Whereas, for the larger rule collections, developers can smoothly integrate the rules into the annotated POJOs class. The RuleBook efficiently transforms this package into an organised rule book that simplifies the organisation and management of diverse rules in Java applications.
Example:
Java
public class DelftstackRule { public RuleBook<Object> defineDelftstackRules() { return RuleBookBuilder.create() .addRule(rule -> rule.withNoSpecifiedFactType().then(f -> System.out.print("Delftstack"))) .addRule(rule -> rule.withNoSpecifiedFactType().then( f -> System.out.println("The Best Tutorial Site"))) .build(); } } |
5. OpenL Tablets
OpenL Tablets is an open source business rules and decision management system for Java which serves as an integral component in the both business rule engines and the management systems. Its adaptability and extensibility make it a valuable tool for the developers who seek for robust solutions to implement, organise, and manage their business rules effectively in the Java applications, it also ensures the efficient decision making processes.
Example:
Java
// Define a rule in OpenL Tablets public class Rules { public boolean exampleRule(int property) { return property > 10; } } |
6. Eclipse OCL (Object Constraint Language)
Eclipse OCL (Object Constraint Language) goes beyond being a rule engine as it’s a specialised language which is designed for expressing the rules on objects within UML models. Its distinctive capability enables the developers to precisely define and enforce the rules and shapes the behaviour and relationships of the objects in their Java applications, also making the Eclipse OCL a valuable asset for ensuring accuracy and compliance with the specified criteria in such complex application scenarios.
Example:
Java
// Define a constraint context SomeObject inv: self.property > 10 |
7. Apache Jena Rules
Apache Jena rules is a Java framework for constructing the semantic web and linked data applications that showcase the powerful rule engine which is designed for handling the RDF data. This framework provides developers with robust tools to navigate, query, and deduce the relationships within RDF datasets, also making it an essential asset for those who are engaged in the development of advanced applications involving semantic web technologies.
Example:
Java
// Define a rule in Jena String ruleString = "[r1: (?x ex:property ?y) -> (?x ex:flag true)]"; Reasoner reasoner = new GenericRuleReasoner(Rule.parseRules(ruleString)); |
8. Nools
Nools is recognized as a rule engine for Node.js which effortlessly extends its utility to Java through the assistance of the Nashorn JavaScript engine which is included in the Java Development Kit (JDK) starting from Java 8. This compatibility enhances developers ability to utilise the Nools’ rule based capabilities, and it’s originally designed for Node.js, within Java applications, and this rule offers a flexible solution for implementing and managing rules across the different environments.
Example:
Java
// Define a rule in Nools (JavaScript syntax) define SomeRule { when { $s: SomeObject $s.property > 10 } then { $s.flag = true; } } |
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.