Codepocalypse Now: LangChain4j vs Spring AI
Abstract
ChatGPT can write code. Copilot can autocomplete. But can Java build a real AI agent — one that manages your calendar, reads your email, and remembers who you are across sessions? OpenClaw, the viral personal AI agent with 350K GitHub stars, proves the concept. We’re going to build it. Twice. In Java. Live on stage. Baruch brings Spring AI. Viktor brings LangChain4j. Same features, same LLM, same use case — completely different philosophies. Six rounds: basic agent, memory, tool calling, agentic workflows, guardrails, and observability. Each round exposes a fundamental design disagreement: Is memory an Advisor or a Provider? Are agents composed services or first-class citizens? Do you need MCP or can models call APIs directly? This isn’t just a framework comparison. It’s an abstraction war — and the winner tells you something about how YOUR team should architect AI into your Java applications.
Resources
Frameworks
- Spring AI — Spring’s AI framework. ChatClient, Advisors, tool calling, MCP.
- Spring AI 2.0 Migration Guide — Breaking changes from 1.1 to 2.0.
- LangChain4j — Java LLM framework. AiServices, agents, MCP, guardrails.
- LangChain4j Agentic Module — Supervisor, sequential, parallel, conditional workflows.
- Spring Boot 4.0 Release Notes — Jackson 3, Jakarta EE 11, starter renames.
- Quarkus LangChain4j — @RegisterAiService, MCP, guardrails in Quarkus.
OpenClaw / NanoClaw
- OpenClaw — The viral personal AI agent (350K+ GitHub stars).
- NanoClaw — Minimalist, containerized alternative to OpenClaw.
- ClawRunr / JavaClaw — “We didn’t build anything new. We connected the pieces that were already there.”
MCP (Model Context Protocol)
- MCP Specification — The protocol specification.
- developer-events MCP — Conference CFP MCP server by Oleg Shelajev (used in the demo).
- developers.events — The conference CFP data source.
TUI4J
- TUI4J — Terminal User Interface framework for Java (Bubble Tea port).
- Brief — Terminal AI chat client built with TUI4J.
Tessl
- Tessl — Agent Enablement Platform — Package manager for agent skills and context.
- Tessl Registry — Browse and install tiles.
- Tessl Documentation — Getting started with tiles, evals, and context engineering.
Tools
- presenterm — Terminal-based markdown presentation tool (used for the slides).
- Claude Code — The coding agent used to build the demo.
Previous Codepocalypse Versions
- DevoxxFR 2025 — 3-hour competitive coding showdown.
- Dev2Next 2025 — Live-coded comparative demo.
- DevFest Toulouse 2025 — 45-min competitive coding with audience voting.
Conference
- Arc of AI 2026 — Austin, TX, April 13–16, 2026.
Speakers
- Baruch Sadogursky — speaking.jbaru.ch — All talks, slides, and shownotes.
- Viktor Gamov — speaking.gamov.io — Viktor’s speaker profile.
- @jbaruch on Twitter/X
- @gamussa on Twitter/X