There are two SOAP development approaches:
contract-first: From XSD Schema. Recommend by Spring Boot
contract-last: From source code. Possible, but not supported out-of-the-box by Spring Boot
Using SOAP with Java Spring Boot: A Step-by-Step Guide [contract-first]
https://abhinnpandey.medium.com/using-soap-with-java-spring-boot-a-step-by-step-guide-16d1e0643840
Creating a SOAP Web Service with Sprin [contract-first]
https://www.baeldung.com/spring-boot-soap-web-service
Contract-last Spring Web Services [contract-last]
https://blog.termian.dev/posts/contract-last-spring-ws/
JAX-WS integration with Spring [contract-first & contract-last]
As of 2024-sep, it only supported Spring Boot 2 (javax) but ongoing work was taking place for supporting Spring Boot 3 (jakarta)
https://github.com/revinate/jaxws-spring