Spring Boot 4 Migration

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Skill
Workflow
Software development
MIT
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From the author

Migrate a Spring Boot 3.x application to Spring Boot 4.0 (Spring Framework 7, Jackson 3, modular starters, JSpecify). Use only for an explicit Boot 3.x to 4 migration, or to fix build or test failures caused by it, or to review one. Not for 3.x patch bumps or 4.0 to 4.1 upgrades; follow the target Boot version release notes and upgrade guide for those. Covers Maven and Gradle (Kotlin DSL, version catalogs).

— the description by jdubois

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a systematic approach to upgrading Spring Boot applications from version 3.x to 4.0. It covers critical architectural changes, including the shift to Spring Framework 7, Jackson 3, and modular starters. The workflow emphasizes a methodical, incremental migration process—starting with a baseline at the latest 3.5.x version—to ensure build stability and test integrity throughout the transition. It supports both Maven and Gradle (including Kotlin DSL and version catalogs) and provides guidance on handling configuration properties, testing framework updates, and observability modules.

What it does

Guides the user through a multi-step migration process from Spring Boot 3.x to 4.0.
Provides instructions for updating build configurations in Maven and Gradle.
Details the transition to modular starters and Jackson 3.
Offers a checklist for verifying build, tests, and runtime health.
Includes references for specific migration topics like testing, security, and observability.
Suggests using OpenRewrite recipes where available to automate parts of the migration.

When to use it

When performing an explicit migration from a Spring Boot 3.x application to 4.0.
When troubleshooting build or test failures specifically caused by a 3.x to 4.0 migration.
When reviewing a codebase that has undergone a 3.x to 4.0 migration.
When you need to identify the correct order of operations for updating dependencies and configuration.

Advantages

Promotes a safe, incremental migration strategy that minimizes breaking changes.
Provides clear guidance on handling complex changes like Jackson 3 and modular starters.
Supports both Maven and Gradle build systems.
Includes a final verification checklist to ensure application stability.
Directs users to official documentation for deep-dive technical details.

Usage examples

“How do I start migrating my Spring Boot 3.2 application to 4.0?”: The agent will guide you to first upgrade to the latest 3.5.x version, establish a baseline with passing tests, and then proceed with the 4.0 migration steps.
“I am getting build errors after updating to Spring Boot 4.0 regarding Jackson. What should I do?”: The agent will point you to the Jackson 3 migration reference, explaining the package renames and the use of the temporary compatibility module.
“How should I handle the new modular starters in my Gradle build?”: The agent will explain the difference between technology-specific starters and classic starters, providing examples for your libs.versions.toml and build.gradle.kts files.

Install

Download the skill as a ZIP:
https://mp-staging.autogineer.com/agent-skills/github/spring-boot-4-migration/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip spring-boot-4-migration.zip -d .agents/skills

Documentation by jdubois

Spring Boot 3.x to 4.0 Migration

Step-by-step migration workflow. Topic details live in references/; load only the files relevant to the current step.

Rules

Never read or print secrets (.env, credentials, tokens in properties files).
Change one thing per step and run the test suite after each step; commit nothing you cannot build.
Pin versions explicitly; never use latest or open-ended ranges.
Check the official sources when unsure: the Spring Boot 4.0 Migration Guide on the Spring Boot GitHub wiki and the release notes on spring.io.

Workflow

Detect the current state
- Boot version: pom.xml (spring-boot-starter-parent / BOM version), build.gradle(.kts) (org.springframework.boot plugin), or gradle/libs.versions.toml.
- Build tool: pom.xml + mvnw means Maven; build.gradle.kts / build.gradle means Gradle (Kotlin or Groovy DSL). Use the project wrapper (./mvnw, ./gradlew).
- Java version (Boot 4 needs Java 17+, Java 25 recommended), Kotlin version, and key libraries (Jackson, Hibernate, Security, Kafka, Elasticsearch, MongoDB).
- See prerequisites.
Migrate to the latest 3.5.x first. If the project is older than 3.5, upgrade to the latest 3.5.x, fix deprecation warnings, and get the tests green before touching 4.0. Never jump from 3.2 straight to 4.0.
Baseline: run the full build and tests (./mvnw verify or ./gradlew build) and record failures that exist before migration.
Bump to 4.0.x (parent/BOM or plugin version) and fix the build in this order, running the build after each item:
1. Starters and modules: starters and removed features. Choose either the classic starters or the new modular ones; Boot 4 split the auto-configuration into many modules, and each technology now has its own *-test starter.
2. Build files and third-party dependencies: build and dependencies and Kotlin/Java build config.
3. Jackson 3 (new tools.jackson packages): Jackson 3. A temporary Jackson 2 compatibility module exists; plan to remove it.
4. Core framework (JSpecify nullability, package relocations, logging, DevTools, PropertyMapper): core framework.
5. Configuration properties (MongoDB, Spring Session, persistence, Kafka retry): configuration properties. Add spring-boot-properties-migrator temporarily to find renamed keys, and remove it afterwards.
6. Web and messaging changes (trailing slash matching, HttpMessageConverters, Jersey, Kafka, RabbitMQ): web and messaging.
7. Tests (Mockito/@MockBean replacement, @SpringBootTest changes, @PropertyMapping): testing.
8. Actuator and observability modules, health probes: actuator and observability.
Verify with the checklist, pitfalls and resources: full build, tests, startup, actuator health, a smoke test of the main endpoints, and native image build if used.

Build tool notes

Maven: change the parent (or spring-boot-dependencies BOM) version, then swap starters in <dependencies>. Use ./mvnw dependency:tree to find stale transitive Jackson 2, Undertow, or Spring Retry usage. The reference files show Gradle snippets; translate the coordinates directly to Maven <dependency> entries.
Gradle Kotlin DSL: update the plugin version in plugins {} or the version catalog; use ./gradlew dependencies --configuration runtimeClasspath to inspect resolution.
Keep the Spring Boot version in a single place (parent, BOM property, or version catalog entry).

Reference files

File	Topic
01-prerequisites.md	Minimum versions, pre-migration steps
02-starters-and-removed-features.md	Modular starters, renamed starters, removed servers/features
03-jackson-3.md	Jackson 3 packages, renames, compatibility module
04-core-framework.md	JSpecify, package moves, logging, DevTools, PropertyMapper
05-build-and-dependencies.md	Gradle plugin, Spring Retry, Authorization Server, Elasticsearch, Hibernate
06-configuration-properties.md	Renamed and restructured properties
07-web-and-messaging.md	Web framework, Kafka, RabbitMQ changes
08-testing.md	Test framework changes
09-actuator-and-observability.md	Actuator, Micrometer and OpenTelemetry modules
10-kotlin-and-java-build-config.md	Kotlin compiler and Java preview configuration
11-checklist-pitfalls-resources.md	Final checklist, pitfalls, links

Automation

Use OpenRewrite (org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0, https://docs.openrewrite.org/recipes/java/spring/boot4/upgradespringboot_4_0-community-edition) when available, review the diff, and always fetch the version-specific official guide before editing.

Upstream sources (read before migrating)

Fetch the page for the target version; prefer it over this skill when they conflict.

Boot 4.0 Migration Guide: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Migration-Guide
Boot 4.0 Release Notes: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Release-Notes
Upgrading Spring Boot (incl. spring-boot-properties-migrator): https://docs.spring.io/spring-boot/upgrading.html
System requirements: https://docs.spring.io/spring-boot/system-requirements.html
Boot releases: https://github.com/spring-projects/spring-boot/releases
Spring Framework 7: https://github.com/spring-projects/spring-framework/wiki/Upgrading-to-Spring-Framework-7.x, https://github.com/spring-projects/spring-framework/wiki/What%27s-New-in-Spring-Framework-7.x
Spring Security 7: https://docs.spring.io/spring-security/reference/migration/index.html
Spring Data 2025.1: https://github.com/spring-projects/spring-data-commons/wiki/Spring-Data-2025.1-Release-Notes
Spring Batch 6: https://docs.spring.io/spring-batch/reference/whatsnew.html
Hibernate ORM 7: https://docs.hibernate.org/orm/7.0/migration-guide/
Jackson 3: https://github.com/FasterXML/jackson/blob/main/jackson3/MIGRATING_TO_JACKSON_3.md
Micrometer: https://github.com/micrometer-metrics/micrometer/wiki/Migration-Guide

For Boot 3.x patch bumps or Boot 4.0 to 4.1 upgrades, go directly to the target Boot version's release notes and upgrade guide using the official links above. These are dependency upgrades, not JDK migrations; do not route them to java-upgrade.

Related skills, each only if installed (otherwise use the fallback in parentheses):

spring-security (Security 7 changes): fall back to the Spring Security 7 migration guide above.
spring-observability: fall back to actuator and observability and the Micrometer guide above.
java-hibernate-jpa: fall back to the Hibernate ORM 7 migration guide above.
java-upgrade (only when a JDK upgrade is explicitly requested): fall back to the target JDK's official migration guide.
java-diagnostics (runtime or startup failures): read the full stack trace and mvn dependency:tree / gradle dependencies output yourself.
java-testcontainers (Testcontainers 2.0 tests): see testing and the Testcontainers 2 migration notes.
kotlin-springboot (Kotlin specifics): see Kotlin and Java build config.

Files

ATTRIBUTION.mdAdded by AutoGineer877 B
LICENSELicence file added by AutoGineer1.0 KiB
SKILL.md8.4 KiB
references/01-prerequisites.md1.9 KiB
references/02-starters-and-removed-features.md9.6 KiB
references/03-jackson-3.md4.2 KiB
references/04-core-framework.md4.2 KiB
references/05-build-and-dependencies.md6.2 KiB
references/06-configuration-properties.md3.0 KiB
references/07-web-and-messaging.md7.3 KiB
references/08-testing.md6.0 KiB
references/09-actuator-and-observability.md2.7 KiB
references/10-kotlin-and-java-build-config.md1.3 KiB
references/11-checklist-pitfalls-resources.md5.9 KiB

LICENSE

MIT License

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Requirements and compatibility

Written for: GitHub Copilot

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