Error deploy spring-boot 2.5.x app in Websphere 8.5.5 throw java.lang.NoClassDefFoundError: javax.servlet.http.HttpSessionIdListener
Solution 1:
Spring Boot 2.5 requires Servlet 3.1 / Java EE 7.
WebSphere 8.5 is Servlet 3.0 / Java EE 6 only.
You'll need WebSphere 9.0 for support of Servlet 3.1. / Java EE 7 as required by Spring Boot 2.5.