Aa somebody who has had to do a Spring upgrade in the past, from 2.x to 4.x, I suggest you do Spring first, then the JDK after. Spring still supports 8 well aft

Aa somebody who has had to do a Spring upgrade in the past, from 2.x to 4.x, I suggest you do Spring first, then the JDK after. Spring still supports 8 well after it starts supporting 11. Once you reach a certain version of Spring, upgrading the JDK is as simple as changing a 1.8 into an 11. I don't know PrimeFaces, but I have worked with JSP, which does have a flag to set the compiler version (in case you were ever thinking about putting java lambda's in JSP files, which is possible but not recommended due to mixing code). The hardest part of upgrading the JDK is going from 8 to 9. After 9 it is much more forgivable. As for Spring, major versions are a pain, as is Hibernate. The other parts of Spring are generally well upgradable if you read the Spring changelogs.