Moving to the Next Generation of Spring Boot

Spring Boot 4 marks a significant leap forward in JVM application development. Built on Spring Framework 7 and Jakarta EE 11, it brings enhanced performance, modern Java capabilities, and declarative programming models to enterprise microservices.

Moving from Spring Boot 3.x to 4.x is more than a routine version bump. Executing a Spring Boot 4 Migration introduces critical architectural changes that help developers write cleaner, safer, and more maintainable code while reducing boilerplate across the entire tech stack."

Major Features and Architecture Improvements

JSpecify Null-Safety StandardSpring Boot 4 replaces internal @Nullable annotations with JSpecify standard (@NullMarked), establishing package-wide non-null defaults that major IDEs and static analysis tools recognize natively.
Declarative HTTP ClientsBuilding on @HttpExchange, Spring Boot 4 introduces @ImportHttpServices. This allows developers to auto-register declarative HTTP clients without hand-crafting proxy factories or custom RestTemplate beans.
Built-in API VersioningTeams no longer need custom interceptors or complex URL mapping to manage API changes. Spring Boot 4 migration adds direct version attributes to @RequestMapping shortcuts, configurable via headers, paths, or media types.
Jackson 3 IntegrationThe framework transitions from Jackson 2 to Jackson 3, introducing dedicated JsonMapper and XmlMapper beans. (Note: Exception handling changes from checked IOException to unchecked RuntimeException.)

Essential Steps for a Smooth Migration

Prerequisites: Ensure your runtime environment is updated to Java 17 or higher (Java 21/25 recommended) and build tools match Gradle 8.14+ or current Maven releases.
Audit Dependencies: Check third-party libraries for Jakarta EE 11 compatibility and update Jackson 2 configurations to Jackson 3 builders.
Refactor Annotations: Update package-level nullability annotations to JSpecify @NullMarked and align controller mappings with native API versioning.

The Journal

How to Migrate to Spring Boot 4: Complete Upgrade Strategy