Spring Boot Migration

Purpose

Use this skill for phased upgrade work on existing Spring Boot applications. This skill adds value through the migration scanner, the Boot 4 / Modulith 2 / Testcontainers 2 reference guides, and a strict migration order that avoids mixing too many changes at once.

Critical rules

• Never migrate blindly. Scan the codebase first.
• Never apply every migration at once. Follow phased upgrades.
• Treat Spring Boot 4, Spring Modulith 2, and Testcontainers 2 as the intended target stack for this skill unless the user asks for a narrower target. Boot 4's Java baseline is 17; recommend Java 25 for new compile targets but do not force an upgrade past what the migration actually requires.
• Verify after each phase and stop when failures appear.

Workflow

Step 1: Scan the project

Use the migration scanner before planning or editing. It reads pom.xml, build.gradle, or build.gradle.kts (whichever the project has) plus Java sources, properties files, and Flyway migrations: