jackson-3-migration

Jackson 2 → 3 Migration

Systematic migration from Jackson 2.x (com.fasterxml.jackson) to Jackson 3.x (tools.jackson). Combines an automated OpenRewrite pass for mechanical Java changes with explicit manual steps for Kotlin-specific patterns that OpenRewrite does not cover, followed by build+test verification.

When to Use

• A Nav service depends on com.fasterxml.jackson.* and needs to move to Jackson 3.x (e.g. for Spring Boot 4 compatibility)
• Build fails after a transitive dependency bump pulls in Jackson 3
• Recurring "fix Jackson migration" requests — use this skill instead of re-deriving the rules each time

Pre-flight Checks

1. Confirm baseline JDK is 17+ (java -version, sourceCompatibility in Gradle). Jackson 3 does not run on Java 8/11 — stop and flag if not met.
2. Confirm the frameworks that actually carry Jackson 3 support are in place first: Spring Boot 4.0+ (Boot 3.x is Jackson 2 only) and Ktor 3.4.0+ (required for ktor-serialization-jackson3).
3. Check for internal version skew — a hardcoded version string elsewhere in the build can contradict the version catalog, and the catalog may not be a local file you can grep. Ask Gradle: ./gradlew dependencyInsight --dependency <artifact> --configuration compileClasspath.
4. Target Jackson 3.1+ (LTS). Jackson 3.0.x is a transitional, non-LTS release — avoid pinning to it if 3.1+ is available.
5. After migrating, confirm no stray Jackson 2.x databind/core remains on the classpath (./gradlew dependencies --configuration compileClasspath | grep jackson) — a leftover 2.x jar lets old com.fasterxml.jackson.databind.* imports keep compiling with no error.
6. If the service uses Ktor content negotiation, swap ktor-serialization-jackson for ktor-serialization-jackson3 (package io.ktor.serialization.jackson3.*, jackson3 { ... } DSL) — the old artifact stays on Jackson 2 and is not drop-in compatible.

Failure modes, exact commands and reasoning for steps 2, 3, 5 and 6: references/dependency-preflight.md.