Spring Boot 4.0 Migration Overview

New baselines

The Spring Boot 4.x migration introduces new baselines for Java, Jakarta, Spring Framework, testing, serialization, and major third-party libraries.

Java 17 minimum (Java 25 recommended)
Jakarta EE 11
Spring Framework 7
Jackson 3.x
JUnit 6
Hibernate 7
Kafka 4.1
Elasticsearch 9

Sample code

1 @RestController
2 public class AccountController {
3 
4 	@GetMapping(path = "/account/{id}", version = "1.1")
5 	public Account getAccount() {
6 	}
7 }

Modularizing Spring Boot

https://spring.io/blog/2025/10/28/modularizing-spring-boot

When Spring Boot 1.0 was released in 2014, it shipped with a single spring-boot-autoconfigure jar weighing in at 182 KiB. The autoconfigure jar grows. With Spring Boot 3.5, that single spring-boot-autoconfigure jar is now 2 MiB!.
Instead of a single, monolithic spring-boot-autoconfigure jar, we are now splitting functionality into small and more focused modules. Every technology supported by Spring Boot now has its own starter, some of which are new in Spring Boot 4.

Adjust Manual or Custom Configuration

If your project or any custom starter previously depended on spring-boot-autoconfigure or pulled in auto-configuration classes manually, you will need to replace those imports/dependencies with the new modular equivalents. You’ll also need to update package names if you reference Spring Boot’s packages. Because modules now begin with org.springframework.boot.<module>

Module Dependencies Starters List

https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Migration-Guide#starters

Deprecated Starters

https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Migration-Guide#deprecated-starters

Deprecated Starter	Replacement
spring-boot-starter-oauth2-authorization-server	spring-boot-starter-security-oauth2-authorization-server
spring-boot-starter-oauth2-client	spring-boot-starter-security-oauth2-client
spring-boot-starter-oauth2-resource-server	spring-boot-starter-security-oauth2-resource-server
spring-boot-starter-web	spring-boot-starter-webmvc
spring-boot-starter-web-services	spring-boot-starter-webservices

Spring Boot 3.x Deprecated API’s

Spring Boot 4.x removes a large portion of APIs deprecated across the 2.x and 3.x lines. In total, 36 deprecated classes—roughly 88% of all deprecations—have been removed.

Deprecated API’s in spring boot 3.5: https://docs.spring.io/spring-boot/3.5/api/java/deprecated-list.html Deprecated API’s in spring boot 2.7.18: https://docs.spring.io/spring-boot/docs/2.7.18/api/deprecated-list.html

Upgrading Jackson

Upgrading Jackson: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Migration-Guide#upgrading-jackson
Major changes/features in 3.0: https://github.com/FasterXML/jackson/wiki/Jackson-Release-3.0#major-changesfeatures-in-30

Articles:

@RestController
public class AccountController {

	@GetMapping(path = "/account/{id}", version = "1.1")
	public Account getAccount() {
	}
}

Deprecated Starter

Replacement

spring-boot-starter-oauth2-authorization-server

spring-boot-starter-security-oauth2-authorization-server

spring-boot-starter-oauth2-client

spring-boot-starter-security-oauth2-client

spring-boot-starter-oauth2-resource-server

spring-boot-starter-security-oauth2-resource-server

spring-boot-starter-web

spring-boot-starter-webmvc

spring-boot-starter-web-services

spring-boot-starter-webservices

1	@RestController
2	public class AccountController {
3
4	@GetMapping(path = "/account/{id}", version = "1.1")
5	public Account getAccount() {
6	}
7	}