OpenL Tablets Technology Stack

Last Updated: 2025-11-05 Version: 6.0.0-SNAPSHOT

Overview

OpenL Tablets is built on modern Java enterprise technologies with a multi-tiered architecture spanning from low-level bytecode generation to high-level web frameworks.

Core Technologies

Java Platform

  • Java Version: JDK 21+ (Required)
  • Module System: Traditional JAR-based (pre-JPMS)
  • Build Tool: Maven 3.9.9+
  • Packaging: Standard Maven multi-module project

Language Features Used

  • Annotations: Extensive use of custom annotations
  • Reflection: Runtime type introspection
  • Bytecode Generation: ASM library for dynamic class creation
  • Dynamic Proxies: ASM-based proxy generation

Framework Stack

Spring Framework Ecosystem

| Component | Version | Purpose | |———–|———|———| | Spring Framework | 6.2.11 | Core container, DI, AOP | | Spring Boot | 3.5.6 | Application framework, auto-configuration | | Spring Security | 6.5.5 | Authentication, authorization | | Spring Integration | 6.5.2 | Enterprise integration patterns |

Usage:

  • Spring is optional for core engine
  • Required for OpenL Studio and RuleService modules
  • Integration point: org.openl.spring module

Jakarta EE Components

| Component | Version | Purpose | |———–|———|———| | Jakarta Servlet API | 6.0.0 | Web layer | | Jakarta Enterprise (CDI) | 4.0.1 | Dependency injection | | Jakarta Faces (JSF) | 4.0.12 | Component-based UI (legacy) | | Jakarta XML Bind (JAXB) | 4.0.4 | XML serialization |

Note: Using Jakarta namespace (Java 11+ migration from javax.*)

Web Frameworks

| Component | Version | Purpose | |———–|———|———| | RichFaces | 10.0.0 | JSF component library (forked, maintained by OpenL) | | Weld Servlet | 5.1.6 | CDI container | | Apache CXF | 4.1.3 | JAX-RS/REST services |

Frontend Technologies

Modern Frontend (studio-ui)

| Technology | Version | Purpose | |————|———|———| | React | 19.2.x | UI library | | TypeScript | 5.9.x | Type-safe JavaScript | | Ant Design | 6.2.x | Component library | | React Router | 7.13.x | Routing | | Zustand | 5.0.x | State management | | i18next | 25.8.x | Internationalization |

Build Tools

| Tool | Version | Purpose | |——|———|———| | Webpack | 5.105.x | Module bundler | | SCSS/Sass | 1.97.x | CSS preprocessor | | Frontend Maven Plugin | 1.15.4 | Maven integration | | Node.js | 24.13.x | Runtime for build tools |

Legacy Frontend

  • JSF/RichFaces: Server-side component framework (being phased out)
  • JavaScript/jQuery: Legacy table editor components

Core Libraries

Bytecode Manipulation & Code Generation

| Library | Version | Purpose | |———|———|———| | ASM | 9.9.1 | Bytecode generation for proxies and dynamic types | | ByteBuddy | 1.18.4 | Runtime code generation | | JavaCC | 3.1.1 | Parser generation (BExGrammar) | | JCodeModel | 4.1.0 | Java code generation for OpenAPI |

Critical: ASM is essential for rule execution - generates proxy classes at runtime.

Parsing & Language Processing

| Library | Version | Purpose | |———|———|———| | Groovy | 4.0.30 | Expression evaluation | | Apache Velocity | 2.4.1 | Template engine for code generation | | ANTLR | (Not used - JavaCC instead) | N/A |

Note: BExGrammar (Business Expression Grammar) is defined in JavaCC format.

Excel Processing

| Library | Version | Purpose | |———|———|———| | Apache POI | 5.5.1 | Excel file parsing (XLS/XLSX) | | Excel Builder | Internal | Custom Excel file generation |

Critical: Rules are defined in Excel spreadsheets - POI is essential.

Data & Persistence

Database

| Component | Version | Purpose | |———–|———|———| | Hibernate ORM | 6.6.42 | Object-relational mapping | | Hibernate Validator | 8.0.3 | Bean validation | | HikariCP | 7.0.2 | Connection pooling | | Flyway | 4.2.0.3 | Database migrations (forked by OpenL) | | H2 Database | 2.4.240 | Embedded database (development/testing) |

Supported Databases: PostgreSQL, MySQL, Oracle, SQL Server, H2

Serialization

| Library | Version | Purpose | |———|———|———| | Jackson | 2.21.0 | JSON serialization | | GSON | 2.13.2 | JSON serialization (alternative) | | JAXB | 4.0.4 | XML serialization |

Cloud & Integration

Cloud Storage

| Provider | SDK Version | Purpose | |———-|————|———| | AWS S3 | 2.34.9 | Cloud repository backend | | Azure Blob Storage | 12.31.3 | Cloud repository backend |

Version Control

| Component | Version | Purpose | |———–|———|———| | JGit | 7.3.0 | Git repository support (forked by OpenL) |

Note: OpenL maintains custom forks of JGit and Flyway for specific needs.

Messaging

| Component | Version | Purpose | |———–|———|———| | Kafka | 4.1.0 | Message-driven rule services |

Observability & Monitoring

Logging

| Component | Version | Purpose | |———–|———|———| | SLF4J | 2.0.17 | Logging facade | | Log4j2 | 2.25.2 | Logging implementation |

Tracing & Metrics

| Component | Version | Purpose | |———–|———|———| | OpenTelemetry | 2.20.1 | Distributed tracing, metrics |

Configuration: See /home/user/openl-tablets/Docs/OpenTelemetry.md

Security

Authentication & Authorization

| Component | Version | Purpose | |———–|———|———| | OpenSAML | 5.1.6 | SAML authentication | | Jose4j | 0.9.6 | JWT/JWS/JWE | | Nimbus JOSE JWT | 10.5 | JWT handling | | Bouncy Castle | 1.82 | Cryptography provider |

Security Modes:

  • Standalone (built-in user management)
  • ACL (Access Control Lists)
  • SAML SSO
  • CAS authentication
  • JWT tokens

API & Documentation

OpenAPI

| Component | Version | Purpose | |———–|———|———| | Swagger Core | 2.2.38 | OpenAPI annotations | | Swagger Parser | 2.1.34 | OpenAPI parsing | | OpenAPI Generator | Internal | Custom code generation |

Features:

  • Auto-generates OpenAPI specs from rules
  • Scaffolds client code from OpenAPI specs
  • Spring integration for REST services

Testing

Unit Testing

| Framework | Version | Purpose | |———–|———|———| | JUnit 5 | 5.14.0 | Unit testing framework | | Mockito | 5.20.0 | Mocking framework |

Integration Testing

| Framework | Version | Purpose | |———–|———|———| | TestContainers | 1.21.3 | Container-based integration tests | | TestContainers Keycloak | 2.6.0 | Keycloak integration tests | | Spring Test | 6.2.11 | Spring testing utilities |

Performance Testing

| Framework | Purpose | |———–|———| | JMH | Microbenchmarking | | Custom profiler | Built-in performance profiling |

Utilities

Apache Commons

| Library | Version | Purpose | |———|———|———| | Commons Lang3 | 3.19.0 | General utilities | | Commons IO | 2.20.0 | I/O utilities | | Commons Collections4 | 4.5.0 | Collection utilities | | Commons Codec | 1.19.0 | Encoding/decoding | | Commons Compress | 1.28.0 | Compression utilities |

Google Guava

| Library | Version | Purpose | |———|———|———| | Guava | 33.5.0 | Core utilities, collections |

AspectJ

| Component | Version | Purpose | |———–|———|———| | AspectJ | 1.9.24 | Aspect-oriented programming |

Web Server

Embedded Server

| Server | Version | Purpose | |——–|———|———| | Jetty | 12.1.3 | Embedded servlet container |

Deployment Options:

  • Standalone WAR deployment
  • Embedded Jetty (Docker)
  • External servlet containers (Tomcat, etc.)

Development Tools

Build & Packaging

| Tool | Version | Purpose | |——|———|———| | Maven Compiler Plugin | Java 21 | Compiles Java sources | | Maven Surefire | Standard | Unit test execution | | Maven War Plugin | Standard | WAR packaging | | OpenL Maven Plugin | Internal | OpenL rules compilation |

Code Quality

| Tool | Purpose | |——|———| | JaCoCo | Code coverage | | SonarQube | Code quality analysis | | OWASP Dependency Check | Security vulnerability scanning |

Docker

| Component | Version | Requirement | |———–|———|————-| | Docker | 27.5.0+ | Container runtime | | Docker Compose | 2.32.4+ | Multi-container orchestration |

Version Control & CI/CD

Version Control

  • Git: Primary VCS
  • GitHub: Repository hosting

Build Profiles

  • quick - Fast build, skip heavy tests
  • skipTests - Skip all tests
  • perf - Performance-optimized tests
  • sonar - SonarQube integration
  • owasp - OWASP security checks
  • sources - Generate sources/JavaDoc
  • gpg-sign - GPG artifact signing

Architecture Patterns

Design Patterns Used

  1. Factory Pattern: RulesEngineFactory, node binder factories
  2. Builder Pattern: SimpleProjectEngineFactoryBuilder
  3. Strategy Pattern: Instantiation strategies, resolving strategies
  4. Proxy Pattern: ASM-based runtime proxies
  5. Visitor Pattern: Syntax node visitation
  6. Decorator Pattern: Binding wrappers
  7. Observer Pattern: Constraint system
  8. Template Method: Abstract classes with hooks
  9. Repository Pattern: Library registries

Architectural Styles

  • Multi-tier: Parsing → Binding → Execution
  • Plugin-based: Extensible node binders, type libraries
  • Convention over Configuration: Project structure conventions
  • Domain-Specific Language: Business rules in Excel

Technology Decision Rationale

Why Excel for Rules?

  • Business analysts comfortable with spreadsheet format
  • Visual representation of decision logic
  • Easy to review and audit
  • No specialized IDE required

Why ASM for Bytecode?

  • High performance runtime proxy generation
  • Dynamic type creation at runtime
  • Fine-grained control over generated code
  • No runtime compilation overhead (vs. dynamic compilation)

Why JavaCC for Parser?

  • Mature, stable parser generator
  • Better error recovery than hand-written parsers
  • Maintainable grammar definition
  • Strong Java integration

Why Spring Boot?

  • Enterprise-standard framework
  • Auto-configuration reduces boilerplate
  • Extensive ecosystem
  • Production-ready features (health checks, metrics)

Why React for New UI?

  • Modern, component-based architecture
  • Strong TypeScript support
  • Rich ecosystem
  • Better developer experience than JSF

Migration Status

Modern (Current)

  • ✅ Spring Boot 3.x (Jakarta namespace)
  • ✅ React 19.x frontend
  • ✅ Java 21+
  • ✅ Hibernate 6.x
  • ✅ OpenTelemetry observability

Legacy (Being Phased Out)

  • ⚠️ JSF/RichFaces (replaced by React)
  • ⚠️ Some deprecated APIs in org.openl.rules
  • ⚠️ Legacy test infrastructure

Maintained Forks

OpenL maintains custom forks of:

  • RichFaces: Updated for Jakarta EE compatibility
  • JGit: Custom enhancements for OpenL needs
  • Flyway: Custom version for database migrations

Rationale: Upstream projects abandoned or lack required features.

System Requirements

Build Requirements

  • JDK: 21+
  • Maven: 3.9.9+
  • Memory: 2 GB RAM minimum (4 GB recommended)
  • Disk: 2 GB free space

Runtime Requirements

  • JRE: 21+
  • Memory: Varies by deployment (1-8 GB typical)
  • Servlet Container: Jetty 12.x, Tomcat 10.x, or compatible

Development Requirements

  • Node.js: 24.9.0 (for frontend builds)
  • Docker: 27.5.0+ (for integration tests)
  • Git: Any recent version

External Resources

Official Dependencies

  • Maven Central: Primary artifact repository
  • npm: Frontend dependencies

Documentation

  • /home/user/openl-tablets/Docs/ - Project documentation
  • /home/user/openl-tablets/README.md - Build instructions
  • Swagger UI: Auto-generated API docs (runtime)

See Also