The most common: - Kotlin for most of the backend code, but Java for shared libs. We still use Java 8 for some libs which may be used in Android, that's an unfortunate reality
- Gradle for build config
- Spring for application architecture
And few things that may significantly improve your dev process, but are not so common:
- Spring Reactor (and Webflux) for processing data and requests. Takes a time to learn, but it worth it
- Thymeleaf for UI
- Spock for testing. Highly recommended for designing tests
- Testcontainers for integration tests
- Micrometer to see what's going on with your app. I.e., to export all internal metrics to use with Prometheus/Grafana/etc
For the environment
- SDKMan to manager the environment
- Gradle Application plugin or Google's Jib to pacakge your app. First prepares a Zip with all binaries, second a Docker container
- IntelliJ IDEA
- Github Actions - turns out to be the most usable CI. Though the Jetbrains TeamCity may be better for a large team