Upgrade to Spring Boot `2.7.18`

I understand that CloudEvents is firmly rooted on a Java 8 baseline.

It is also true that the entire Spring Boot 2.x generation is based on Java 8 (see here).

CloudEvents' Spring integration significantly lags behind at version 2.4.3, and not even the latest 2.4.x release at that (which is 2.4.13). Although, it is a moot point given 2.4.x as been out of OSS (2021-11-18) and Commercial (2023-02-23) Support for some time now (click "more" to expand the list).

Technically, even Spring Boot 2.7.x is out of OSS support, as of 2023-06-30. While Commercial support does not end until 2029-06-30, it does require users/customers to buy a commercial license to contract the Spring team to patch the 2.7.x release line. Without commercial support, there will simply be no more patch (maintenance) releases to the 2.7.x release line.

It is strongly recommended to upgrade to, or at least provide a version of CloudEvents for, Spring Boot 3.x, based on Java 17.

Java 17 is a LTS version, as is Java 21. Java 24 is already available. Spring Boot 4.0 is on the horizon.

First resolve whether the target is Spring Boot 2.7.18 or a Spring Boot 3.x-compatible release; the issue describes both directions. Review the root pom.xml and spring/pom.xml, then run the existing Maven build and tests to identify compatibility work. Done means the chosen Spring Boot version is declared consistently and the project builds and tests pass.