I Built an AI-Powered CLI That Migrates Legacy Java Code to Java 17/21/25
If you've spent any time in enterprise Java, you know the feeling. You open a service that's been running since 2014 and you're greeted by walls of anonymous inner classes, verbose null checks, Collections.unmodifiableList wrapping a new ArrayList, and switch statements with more break keywords than actual logic.
Individually each pattern takes 30 seconds to fix. But across a codebase with 300 files, it's a week of mechanical work — and that's before you factor in the code review.
So I built java-migrate: a CLI tool that scans your Java files, detects legacy patterns, and sends them to Claude with a precise system prompt to get them modernised. One command, instant diff, no surprises.
What it looks like in practice
