| name | spring-boot-migration |
| description | Use when upgrading an application from Spring Boot 3.5 to Boot 4, completing a Framework 7 migration, replacing modular starters, adopting Jackson 3, or diagnosing post-upgrade failures.
|
Spring Boot 4 Migration
Migrate from the latest Boot 3.5 release and keep business changes outside the upgrade diff.
Required baseline
- Use Java 17 or newer; prefer Java 21 for application builds.
- Use Spring Framework 7, Jakarta EE 11, and a Servlet 6.1-compatible container.
- Upgrade Kotlin to the supported baseline when applicable.
- Use a Boot 4-compatible Spring Cloud release train.
- Use GraalVM 25 or newer for native images.
Migrate modules and starters
Boot 4 splits infrastructure into focused modules and starters.
- Replace
spring-boot-starter-web with spring-boot-starter-webmvc.
- Use dedicated technology starters such as
spring-boot-starter-flyway.
- Use technology-specific test starters; they bring the core test starter transitively.
- Use
spring-boot-starter-security-test for Spring Security test support.
- Use
spring-boot-starter-batch-jdbc when jobs require persistent metadata and restartability.
- Use classic starters only as a temporary migration bridge, then remove them.
Migrate code
- Replace Jackson 2
com.fasterxml.jackson customization with Jackson 3 tools.jackson APIs.
- Replace removed
@MockBean and @SpyBean with framework Mockito bean overrides.
- Add
@AutoConfigureMockMvc when a @SpringBootTest requires MockMvc.
- Replace removed or moved Boot package imports and deleted Boot 3 deprecations.
- Remove Undertow configuration and verify the selected server supports Servlet 6.1.
Configuration workflow
- Add
spring-boot-properties-migrator temporarily.
- Start every supported profile and fix each reported property.
- Remove the migrator before release.
- Compare
/actuator/configprops, logging, JSON, and endpoint behavior against the baseline.
Verification
- Run unit, slice, integration, native, startup, and database migration tests as applicable.
- Verify JSON contracts, security failure responses, actuator exposure, and test slice composition.
- Inspect the dependency tree for old starters, duplicate Jackson generations, and unmanaged versions.
Examples
- See
examples/good-migration-plan.md and examples/bad-migration-plan.md.
Gotchas
- Agent keeps old starter names because compilation succeeds transitively - use Boot 4 dedicated starters.
- Agent adds both a technology test starter and the classic test starter - avoid duplicate test graphs.
- Agent leaves Jackson 2 and Jackson 3 customizations together - migrate the complete JSON boundary.
- Agent expects plain Batch starter metadata to persist - use the JDBC starter when restartability matters.
- Agent leaves the properties migrator or classic starters installed - remove temporary migration aids.
