Upgrade Spring Boot to 4.0.0

[meysholdt]

Spring Boot Migration Report

Version Summary

Component	Original Version	Target Version
Spring Boot	3.5.0	4.0.0
Java	17	21

Summary of Code Changes

Build Configuration Changes

• Updated Spring Boot parent version from 3.5.0 to 4.0.0
• Updated Java version from 17 to 21
• Updated spring-javaformat plugin from 0.0.46 to 0.0.47
• Updated Native build tools plugin from 0.10.6 to 0.11.0
• Updated CycloneDX plugin from 2.3.1 to 3.0.0
• Renamed spring-boot-starter-web to spring-boot-starter-webmvc
• Added explicit testcontainers version 1.21.3
• Added new test dependencies: spring-boot-webmvc-test, spring-boot-data-jpa-test, spring-boot-restclient-test

Package Reorganization

Spring Boot 4.0 reorganized packages as part of modularization:

Old Package	New Package
o.s.b.autoconfigure.cache.JCacheManagerCustomizer	o.s.b.cache.autoconfigure.JCacheManagerCustomizer
o.s.b.test.autoconfigure.web.servlet.WebMvcTest	o.s.b.webmvc.test.autoconfigure.WebMvcTest
o.s.b.test.autoconfigure.orm.jpa.DataJpaTest	o.s.b.data.jpa.test.autoconfigure.DataJpaTest
o.s.b.test.autoconfigure.jdbc.AutoConfigureTestDatabase	o.s.b.jdbc.test.autoconfigure.AutoConfigureTestDatabase
o.s.b.autoconfigure.jdbc.DataSourceAutoConfiguration	o.s.b.jdbc.autoconfigure.DataSourceAutoConfiguration
o.s.b.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration	o.s.b.hibernate.autoconfigure.HibernateJpaAutoConfiguration

API Changes

• Replaced RestTemplateBuilder and TestRestTemplate with RestClient in test code
• Updated test assertions in CrashControllerIntegrationTests for error handling changes

Verification Steps Executed

Step	Command	Result
Compile main code	./mvnw compile	✅ SUCCESS
Compile test code	./mvnw test-compile	✅ SUCCESS
Run all tests	./mvnw test	✅ 58 tests passed
Package application	./mvnw package	✅ SUCCESS
Start application	java -jar target/spring-petclinic-4.0.0-SNAPSHOT.jar	✅ Running
Health check	curl http://localhost:8080/actuator/health	✅ {"status":"UP"}