This is a working example of a Hessian-based web service in a Spring Boot application without HessianServiceExporter.
If you search for something like "Hessian Spring integration" you get a lot of examples that use Spring's HessianServiceExporter but it was deprecated in Spring 5.3 and then removed in Spring 6, so now you have to use HessianServlet directly: extend it so that it implements your service interface and then use Spring's ServletRegistrationBean to enable it. On the servlet you should also enable the whitelisting of allowed classes to be safer.
The demo provides two POMs: the main one uses Spring Boot 3.2.0, so it needs Java 17+ and hessian-jakarta; the alternative one uses Spring Boot 2.7.18, so it works with Java 8+ and the classic hessian library.