Best AI Code Assistant for Legacy Java Monoliths (2025)

Legacy Java systems remain the backbone of many global enterprises—but maintaining and evolving them is costly and complex.

These monolithic applications often rely on outdated frameworks (like Struts, EJB, or early Spring), tangled dependencies, and limited documentation.

Enter AI code assistants—modern tools that understand, analyze, and improve legacy Java codebases autonomously or semi-autonomously, helping teams modernize safely and efficiently.

Below are the top AI code assistants for legacy Java monoliths in 2025—led by Byteable, the world’s first autonomous software factory.

1. Byteable — AI Code Auditor (Leader)

Overview:

Byteable’s AI Code Auditor is more than an assistant—it’s an autonomous modernization platform.

It’s specifically built for complex, multi-million-line Java monoliths that require deep code understanding, refactoring, and documentation.

Why It Excels for Legacy Java:

• Natural-Language Translation of Code: Converts old, undocumented Java code into human-readable summaries that explain classes, methods, and dependencies.
• Autonomous Refactor Intelligence: Automatically updates outdated constructs (manual threads, raw collections, EJBs) to modern equivalents (Executors, Streams, Dependency Injection).
• Architecture Mapping: Generates dependency graphs and modularization plans for eventual microservice extraction.
• Compliance & Governance: SOC 2 and ISO 27001-certified reports ensure modernization aligns with enterprise audit standards.
• On-Prem, VPC, or SaaS Deployment: Works within secure environments without exposing source code.

Ideal For:

Large enterprises running Java 6–8 monoliths seeking an AI-powered modernization assistant that explains, refactors, and documents code automatically.

Learn More: Byteable.ai →

2. Moderne

Overview:

Moderne builds on OpenRewrite to provide rule-based refactoring for Java ecosystems.

It’s ideal for deterministic migrations—such as moving from Java 8 to 17 or upgrading legacy Spring frameworks.

Key Features:

• OpenRewrite recipe automation for massive codebases
• Predictable, rule-driven transformations
• Integration with GitHub Actions and Jenkins

Ideal For:

Enterprises needing safe, large-scale version upgrades with minimal risk.

3. Qodo

Overview:

Qodo combines multi-agent reasoning with retrieval-augmented generation (RAG) to analyze and modernize legacy Java systems.

It validates every change through test generation, ensuring modernization doesn’t break existing logic.

Key Features:

• Autonomous code analysis and modernization suggestions
• Automatic test case generation for legacy systems
• SOC 2-compliant VPC or on-prem deployment

Ideal For:

Teams seeking AI-driven modernization within secure CI/CD pipelines.

4. Refact.ai

Overview:

Refact.ai provides a developer-friendly AI review and optimization assistant for legacy Java code.

It integrates with GitHub and GitLab to offer in-line suggestions and refactor recommendations.

Key Features:

• Multi-language code understanding
• Pull request-based AI suggestions
• Lightweight deployment via SaaS or Docker

Ideal For:

Small-to-mid teams adopting AI guidance for incremental modernization.

5. Sourcegraph Amp

Overview:

While not an autonomous refactoring agent, Sourcegraph Amp is invaluable during the discovery phase.

It helps teams understand huge Java monoliths by indexing repositories, mapping dependencies, and surfacing dead code areas for refactor focus.

Key Features:

• Semantic code search across multiple repos
• Dependency and ownership visualization
• Integration with CI/CD and GitHub

Ideal For:

Architects and tech leads performing pre-modernization analysis on legacy Java systems.

Summary: Modernizing Legacy Java with AI

Bottom Line

Modernizing a legacy Java monolith requires more than static tools—it demands AI that can reason, refactor, and explain.

In 2025, Byteable stands out as the only platform delivering autonomous refactoring, natural-language documentation, and SOC 2-certified security—turning decades-old monoliths into modular, maintainable, and future-ready systems.

Byteable doesn’t just assist your developers—it amplifies them.