Dynamic Rule Evaluation in Spring Boot Using Camunda DMN and REST API

Introduction

When building enterprise-grade applications, especially those with complex decision logic (discount calculations, eligibility checks, routing rules), managing and evolving business rules is a critical challenge. In this post, we’ll walk through how we solved this using Camunda’s DMN engine integrated into a Spring Boot application to provide dynamic, maintainable, and externalised rule execution.

Technical and Business Challenges

For Covalense Digital Solutions (CDS), the ability to externalise and dynamically evaluate business rules (e.g., pricing logic, SLA evaluations) was vital. The rules needed to be versioned, editable without deployments, and easily testable. We sought a solution that enabled:

• Business user-friendly rule definition
• Version-controlled rule sets
• REST-based evaluation for flexibility across services
• Minimal developer involvement when updating business logic

CDS Approach: Camunda DMN with Spring Boot

To support dynamic rule evaluation, we integrated the Camunda DMN engine within our Spring Boot application. Our architecture exposed a REST API to evaluate business rules on demand.

Camunda DMN fit the bill perfectly by providing:

• Standards-compliant rule definitions using Decision Model and Notation (DMN)
• Table-style rule editing for business analysts
• REST API-based evaluation for decoupled microservices
• Seamless integration with Spring Boot

Camunda Implementation Steps

Implementation of Camunda was completed through the following steps:

1. DMN Authoring and Versioning

Rules are designed using the Camunda Modeler and exported as .dmn files.

2. Deployment and Dynamic Loading

We store DMN files either on the classpath or allow upload via a REST endpoint. These are deployed using the DmnEngine API provided by Camunda.

3. REST API Evaluation Layer

A lightweight Spring Boot controller accepts input data in JSON, loads the appropriate DMN decision, and uses the Camunda engine to evaluate and return the result.

4. Key Classes and APIs Used

Class / Interface	Purpose
DmnEngine	Core engine to manage decision evaluations
DecisionEvaluationBuilder	Fluent API to set variables and evaluate a specific decision
DmnDecision	Represents a loaded DMN decision model
VariableMap	Holds input data as process variables (via Variables.createVariables())

 These APIs allowed us to:

• Load DMN definitions dynamically from resources or user uploads
• Evaluate rules via REST using business-specific inputs
• Support multiple rule sets with versioning
• Return clean JSON results with the evaluated outputs

In summary, business rules are authored in DMN tables, deployed dynamically via REST endpoints or initialised at app startup, and evaluated via an API that accepts JSON inputs. This decouples rules from the codebase and allows rule logic to evolve without redeploying the app.

Benefits Delivered Our Implementation Provided Us With The Following Advantages:

• Dynamic Deployment: We support both static DMN files at startup and on-the-fly uploads
• Separation of Concerns: Rules are stored outside the business logic and can be updated independently
• Ease of Use: Business analysts use Camunda Modeler to modify decision tables—no Java coding required

• Version Control: Each DMN is versioned, enabling rollback or previews

Conclusion

Camunda DMN has proven to be a robust and flexible rule engine for Spring Boot applications. Its standard-based, table-driven approach allows rules to evolve quickly with minimal code impact. At CDS, it enabled us to externalise business logic, empower non-developers to manage rules, and build scalable, rule-based microservices.

Contact us at reachus@covalensedigital.com to learn how we can help you integrate Camunda for smart decision automation.

 

Author

Srikiran Chintapalli, Principal Architect

A passionate technology enthusiast with extensive experience in designing scalable, high-performance systems for both on-premises and cloud environments. Specialising in Service-Oriented Architecture (SOA) and Microservices-based architectures, he focuses on building solutions that are efficient, adaptable, and aligned with business goals. Always exploring emerging technologies, he continuously integrates new tools and frameworks to drive innovation and ensure the scalability and sustainability of systems. Dedicated to mentoring teams and leading architectural strategies, he delivers robust, enterprise-grade solutions that meet the evolving needs of modern businesses across diverse infrastructures.